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1988

Dispersion mechanics in underground mineventilationPeter Nicholas StandishUniversity of Wollongong

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Recommended CitationStandish, Peter Nicholas, Dispersion mechanics in underground mine ventilation, Doctor of Philosophy thesis, Department of Civiland Mining Engineering, University of Wollongong, 1988. http://ro.uow.edu.au/theses/1239

DISPERION MECHANICS IN UNDERGROUND MINE VENTILATION

A thesis submitted in fulfilment of the requirements for the award of the degree of

DOCTOR OF PHILOSOPHY

from

THE UNIVERISTY OF WOLLONGONG

by

PETER NICHOLAS STANDISH, BE (HONS)

DEPARTMENT OF CIVIL AND MINING ENGINEERING

1988

Candidates Certificate

This is to certify that the work presented in this thesis

is original and was carried out in the laboratories of

the Department of Civil and Mining Engineering in the

University of Wollongong and in the Elura Mine of the

North Broken Hill Pty Ltd Company in Cobar NSW, and has

not been submitted to any other university or institution

for a higher degree.

Peter Nicholas STANDISH

(i)

TABLE OF CONTENTS

Acknowledgements (i) Summary (ii) List of Symbols (iii) List of Figures (iv) List of Tables (ix)

1.0 INTRODUCTION 1

2.0 THEORETICAL CONSIDERATIONS 5

2.1 TRADITIONAL ASPECTS 5

2.2 DISPERSION MECHANICS - IDEAL FLOW 11

2.2.1 Ideal Mixed Flow Model 13 2.2.2 Ideal Plug Flow Model 14 2.2.3 Pure Convection Model 16

2.3 DISPERSION MECHANICS: NON-IDEAL FLOW 19

2.3.1 Dispersion Model 19 2.3.2 Multiparameters Models 31 2.3.3 Tracer Introduction and Measurement 34

2.4 UNDERGROUND TRACER EXPERIMENTS -LITERATURE DATA 37

2.5 SUMMARY 44

3.0 EXPERIMENTAL INVESTIGATIONS 46

3.1 LABORATORY TESTS 46

3.1.1 Tracer Selection and Detection 47 3.1.2 Apparatus 48 3.1.3 Calibration of Equipment 50 3.1.4 Laboratory Method 52

3.2 LARGE SCALE PROVING TESTS 54

3.3 UNDERGROUND STUDIES 56

3.3.1 Test Sites 56 3.3.2 Equipment Usage 57 3.3.3 Test Method 60

3.4 ADDITIONAL WORK 63

3.4.1 Balloon Release Characteristics 63 3.4.2 Detector Evase 65 3.4.3 2 Drill West Vent Shaft Monitor

Position 66 3.4.4 Lateral Position Detection Trials 67

3.5 TREATMENT OF DATA 69

4.0 RESULTS and DISCUSSIONS 72

4.1 LABORATORY TESTS 72

CONTENTS (continued)

4.2 LARGE TEST RIG RESULTS 74

4.3 UNDERGROUND TESTS 77

4.3.1 2/8 Cross Cut Tests 78 4.3.2 West Vent Shaft - Preliminary Tests 83 4.3.3 West Vent Shaft - Position Tests 90

4.4 POSITIONAL ANEMOMETER TRAVERSE 100

4.5 COMPUTER ANALYSIS OF POSITIONAL RESULTS 101

4.5.1 Tracer Results 102 4.5.2 Anemometer Results 106

4.6 COMPARISON OF TRADITIONAL AND TRACER RESULTS 109

5.0 SIGNIFICANCE OF RESULTS 113

5.1 THEORETICAL ASPECTS 114

5.2 PRACTICAL ASPECTS 120

6.0 CONCLUSIONS 124

7.0 REFERENCES 126

(i)

ACKNOWLEDGEMENTS

I would like to thank my supervisor, Dr. N.I. Aziz,

Senior Lecturer, Department of Civil and Mining

Engineering, for his advice and encouragement during the

course of this work.

I also wish to thank the management of NBH P/L, in

particular the Mine Manager Mr Paul Rouse, for permission

to conduct the underground work at Elura Mine Cobar NSW.

The assistance of the workshop staff in the Department of

Civil and Mining Engineering, University of Wollongong

and that of the staff of Elura Mine, Cobar in

constructing experimental equipment is gratefully

acknowledged.

My thanks also go to David Pelchen, Mining Engineer,

Elura Mine for ungrudgingly staying back after his normal

shift to provide periodic assistance with underground

tests when an extra pair of hands was essential for the

experimental work to be carried out.

Special thanks are also due to Associate Professor

R.W. Upfold for his guidance in the selection of computer

software and equipment.

To all those who have helped, in one way or another, in

the preparation of this thesis I extend my sincerest

thanks.

(ii)

SUMMARY

Application of Dispersion Mechanics to mine ventilation

surveys is studied using C2H2 tracer release and

detection on the 2 Drill level at Elura Mine, Cobar, NSW.

Preliminary calibration work of the measuring systems in

the laboratory and in a large test rig together with the

results obtained is reported. It is found that the

results in these non-mining systems closely follow the

results of Dispersion Mechanics theory for a dispersed

plug flow model.

For the underground conditions studied the results of

tracer studies show that the ventilating air flow is

layered or segregated in a "tube bundle" pattern. These

tracer results are reproduced by the results of

traditional anemometer readings obtained under the same

flow conditions. The results also show that the

ventilating air flow under actual underground conditions

is characterised by transient behaviour which appears to

be a normal behaviour of the ventilating air in

underground workings. Application of the results to

practice is included.

r

A a b C c D

—

-

— — -

-

D M " d E e F f H K L M N P Q R

R S t

t

E u V V

x,y,z

Greek Symbols

« , ^ , ^

A 6 £

V 2

Ah Subscripts

e f d t &

Special Symbols

(D/UL) (D/ud)

Sc R

-

-

—

— -

-

— -

-

-

--—

--

-

-

-

—

-—

-

--—

—

-

-

-

— --

-

—

—

-

(iii)

LIST OF SYMBOLS

Area Area ratio (eqn (2.57)) Time ratio (eqn (2.57)) Concentration constant Dispersion Coefficient Molecular diffusivity

Diameter Exit age distribution Exponential Step function Friction factor Height Constant Length, distance Mass Number of ideal tanks Pressure Mine air flow rate Radius

Specific Resistance Perimeter Time

Mean time

Mean of coordinate mean times Velocity Volume volumetric flow rate Spatial coordinates

Exponents Difference Dirac <5-function Roughness Viscosity

Variance Head Loss

Effective Flowing Dead Real time Dimensionless time

Dispersion Number Dispersion Intensity Schmidt Number

Reynolds' Number

(iv)

List of Figures

Number Title Page

2.1 Friction Factor as a function of Reynolds' number with relative roughness as a parameter after Skochinsky and Komarov (64). 7 A

2.2 Plug flow model. 15A

2.3 Step function response. 15A

2.4 Comparison of plug flow, perfect mixing and laminar flow residence time distributions after Butt (66) 18A

2.5 One dimensional dispersion model. 19A

2.6 Convective and molecular diffusion contributions to dispersion. 22A

2.7 Fe and EQ curves as calculated from

eqns (2.28) and (2.43) for different

values of n [= (D/uL)-1] after Butt (66). 25A

2.8 Intensity of dispersion as a function of Reynolds' number for different Schmidt numbers after Levenspiel (69). 27A

2.9 An example of tracer response curves for fluid flow behaviour in equipment after Levenspiel (69). 31A

2.10 An idealized response curve for parallel flow. 32A

2.11 Idealized response curves to step and pulse inputs for a recirculating flow after Levenspiel (69). 33A

2.12 Test layout of Higgins and Shuttleworth (2). 37A

2.13 Reported tracer response curves (2) for the layout in Fig 2.12. 37A

2.14 Face response curves of Higgins and Shuttleworth (2). 38A

2.15 Calculated Et curves of the data in

Fig 2.14. 3 8 A

2.16 Plan of the USBM experimental mine (3). 41A

(v)

List of Figures (continued)

Number Title Page

2.16 Plan of the USBM experimental mine (3). 41A

2.17 Reported tracer response at position S in the mine of Fig 2.16. 41A

2.18 Response curve of Thimons and Kissell of a recirculating situation (3). * 42A

2.19 Calculated flow model for the response of Fig 2.18. 42A

2.20 Recirculation response curves of Stokes and Stewart (7). 43A

2.21 Calculated flow model for the response of Fig 2.20. 43A

3.1 Line diagram of laboratory apparatus. 48A

3.2 Circuit diagram of detector Tandy

Electronics P/L. 49A

3.3 Calibration curve of pressure vs volume for the vacuum pump. 50A

3.4 Rotating collar flow control device. 50AA

3.5 Diagram of the setup used for detector calibration. 52A

3.6 Detector mV response vs concentration plot. 52AA

3.7 Typical response curve obtained in laboratory tests. 54A

3.8,3.9 Surface test rig and Tracer Input Devices. 54AA

3.10 Typical response curve obtained in the large test rig. 56A

3.11 ' Plan of 4 Drill level. 56AA

3.12 2 Drill Plan with test sites marked. 56AAA

3.13(a) Line of backs, 2/8 Cross cut. 57A

3.13(b) View along drive, 2/8 Cross cut. 57A

3.14 West Vent Shaft detection site. 61A

(vi)

List of Figures (continued)

Number Title Pa

3.15 In situ zeroing of the chart recorder. 61A

3.16 Balloon inflation procedure. 62A

3.17 Close up of tilt valve. 62A

3.18 Balloon in position and ready for release. 6 2 A A

3.19 Recorder tracer of (a) balloon release and (b) plastic bag release. 63A

3.20 Balloon burst from below.

3.21 Balloon burst from below - 1 metre downstream.

64A

64A

3.22 Balloon burst from below - 5 metres downstream. 6 4AA

3.23 Diagram of observed tracer spread. 64AA

3.24 Cone evasfe on site in WVS regulator. 65A

3.25 Evas^ detail. 65A

3.26 Box evasfe 65AA

3.27 Detector position, WVS. 66A

3.28 Expanded plan view of WVS area. 67A

3.29 Expanded plan view of WVS area with sites marked. 68A

3.30 Tracer release points across drive section. g9A

3.31 Relationship between D/uL and the dimensionless E curve (C_) for small

extents of dispersion, after Levenspiel (69). 71A

4.1 Mean time vs velocity. 72A

4.2 D/ud vs Reynolds' number. 72A

4*3 Plot of variance vs velocity - Laboratory Results. 73A

(vii)

List of Figures (continued)

Number Title Page

4.4 Mean time vs velocity for Large test rig 74A

4.5 Log-log plot variance vs velocity, Large test rig data. 74A

4.6 Head loss vs velocity (log-log), large test rig. 77A

4.7 Plot of mean time vs distance; Large test rig. 79A

4.8 Variance vs distance; Large test rig. 80A

4.9 Tracer response in an ideal plug flow vessel. 84A

4.10 Expanded plan view of WVS release points 84A

4.11 Response curve for Test 192. 97A

4.12 Flow model for the response of Fig 4.11. 97A

4.13 Hand drawn velocity contours - Site 1 101A

4.14 Computer generated contour plot - Site 1 101A

4.15 Site 1 positional velocities by tracer, all head positions. 102A

4.16 Site 1 Positional velocities by tracer, central head position only. 102A

4.17 Site 2 positional velocities by tracer. 102AA

4.18 Site 3 positional velocities by tracer. 102AA

4.19 Site 4 positional velocities by tracer. 102AAA

4.20 Site 1 positional velocities by anemometer. 106A

4.21 Site 2 positional velocities by anemometer. 10 6A

4.22 Site 3 positional velocities by anemometer. 1o 6AA

4.23 Site 4 positional velocities by anemometer. 106AA

Number

4.24

4.25

4.26

4.27

4.28

4.29

4.30

4.31

5.1

(viii)

List of Figures (continued)

Title

Site 5 positional velocities by anemometer.

Site 6 positional velocities by anemometer.

Site 7 positional velocities by anemometer.

Site 8 positional velocities by anemometer.

Site 1 positional velocities by anemometer (low velocity).

Site 2 Positional velocities by anemometer (low velocity).

Site 3 positional velocities by anemometer (low velocity).

Site 4 positional velocities by anemometer (low velocity).

Calculated variances () and residual concentrations, %. Site 1 calculated responses.

Page

106AAA

106AAA

106AAAA

106AAAA

108A

108A

108AA

108AA

117A

(ix)

List of Tables

Number Title Page

2.1 Resistance Coefficient Values - k (65) 10

3.1 Properties of C2H2 and Air 47

3.2 Chart Recorder Calibration Results 51

3.3 Chart Recorder Speeds 52

4.1 Results of Air Velocities (m/s) Measured by Two Measurement Techniques 79

4.2 Particulars of Tests 46=*64 85

Al Laboratory Test Results A2-2

A2 Large Test Rig Results Cross Sectional Injection A2-2

A3 Large Test Rig Results Point Injection A2-3

A4 2/8 Results A2-3

A5 Site 1 Results; Positional Release A2-5

A6 Site 2 Results; Positional Release A2-6

A7 Site 3 Results; Positional Release A2-7

A8 Site 4 Results; Positional Release A2-7

A9 Site 1, Anemometer Positional Velocities A3-2

A10 Site 2, Anemometer Positional Velocities A3-2

All Site 3, Anemometer Positional Velocities A3-3

A12 Site 4, Anemometer Positional Velocities A3-3

A13 .. Site 5, Anemometer Positional Velocities A3-4

A14 Site 6, Anemometer Positional Velocities A3-4

(x)

List of Tables (continued)

Number Title Page

A15 Site 7, Anemometer Positional Velocities A3-5

A16 Site 8, Anemometer Positional Velocities A3-5

1

CHAPTER 1

INTRODUCTION

A number of functions are required of air ventilating the

underground environment, beyond the provision of Oxygen

to underground workers. A concise statement of these

functions has been made in a recently published work by

Vutukuri and Lama (1):

1) "To dilute the concentration of the

explosive and toxic gases, fumes and

radon to environmentally safe levels and

to remove from the mine;

2) To dilute the concentration of the airborne

dust to physiologically acceptable levels

and to remove from the mine;

3) To provide a thermally acceptable

environment in which persons can work

without undue discomfort or any danger of

exhaustion from heat from the mine as may

be necessary."

From the above it is evident that in addition to the

knowledge of air quantity, velocity and pressure losses

involved, an understanding of the behaviour of the

ventilating air in actual roadways is necessary.

2

Flow parameters that may influence the above functions of

the ventilating air are its dispersion characteristics as

well as the actual flow patterns involved. Neither of

these flow characteristics can be evaluated by

traditional surveying methods. They can, however, be

measured by tracer gas techniques.

In 1958,Higgins and Shuttleworth (2) reported what may be

one of the earliest investigations into the use of tracer

gases in headings. These authors used NO as a tracer and

restricted their investigations to the measurement of

flow rates and turnover times.

Later, a series of investigations (3-6) was conducted by

the USBM using Sulfur Hexaflouride (SF^) as a tracer. In

addition to the measurement of flow rates and turnover

times, air recirculation, stopping leakage, coal face

ventilation and spray-fan versus conventional ventilation

were investigated.

Recently a tracer study of the behaviour of a tunnel

boring machine (TBM) was reported by Stokes and Stewart

(7). Tracers used were CH4 and CgH0. Although the study

was not carried out underground, the results give an

insight into the possible air movement patterns that may

occur at the face during the coal cutting with the TBM

design used.

3

None of the investigations referred to above considered

dispersion mechanics theory nor the flow models suggested

by this theory in the analysis of the tracer response

curves obtained in the respective works.

As far as is known, there have been no reports so far of

the use of dispersion mechanics to analyse ventilation in

actual underground mine workings. However, dispersion

mechanics has been used in a 1:100 scale hydraulic model

of a three-heading longwall development panel to explore

possible changes in mine ventilation characteristics of a

number of alternative operations as well as simulated

methane emissions at the coal face (8).

Presentation of this work at ventilation symposia (9,10)

raised interest from other investigators in the field of

mine ventilation. It was concluded from the investigation

and the comments arising from presentation of the

findings that the model results of Dispersion Mechanics

could be applied to mine ventilation surveys to provide

quantitative flow patterns and effective dispersion in

the ventilating air. It was also considered that the next

step in the development should involve evaluation of the

method under actual underground mining conditions to

enable general assessments to be made of this new method

in mine ventilation work.

4

The challenge suggested in that work viz: to evaluate

Dispersion Mechanics under actual operating conditions

has been attempted in the Elura mine, often under

difficult conditions. Elura mine, exploiting a Silver,

Lead and Zinc ore body near Cobar N.S.W. produces 1.2 MTA

and employs a main surface fan installation providing a

3

total throughput ventilation of 120 to 140 m /sec. More information on the mine can be obtained from the

proceedings of the 1986 Underground Mine Operators

Conference, held at Kalgoorlie, W.A. (11).

The results of developmental work leading to, and of

actual underground work conducted at the Elura Mine are

presented in this thesis.

7

5

CHAPTER 2

THEORETICAL CONSIDERATIONS

2.1 - TRADITIONAL ASPECTS

The quantity of flowing air underground has traditionally

been of primary interest to researchers in the field of

underground mining ventilation. The importance of the

knowledge of the air quantity is associated with the

assessment of: network designs (12-21), strata gas

control (22-34), ventilation and refrigeration (35-39)

and system analysis (40-45). Additionally, other

ventilation aspects including those associated with fans

(46-52) and diesel emissions (53-57) as well as aspects

of dust control (58-62) require a knowledge of the air

quantity flowing underground.

Historically, air quantity in mines has been evaluated by

the Atkinson's equation below:

An kSL rt2 AP = — j Q (2.1)

A

The sequence of theories culminating in Atkinson's

equation has been presented in Hartman's book entitled

Mine Ventilation and Air Conditioning (63). In reaching

the relationship in eqn (2.1) between the frictional loss

of pressure (Ap) along a driveage (of length L, perimeter

6

S and cross sectional area A) and the flow rate of air

(Q) consideration has been made of other works.

Skochinsky and Komarov (64), in their text on the subject

indicate that for most of the air-flows underground,

pressure losses are directly proportional to the square

of the velocity, ie.

AP=*i^i (2.2)

Equation (2.2) gives the relationship between the head

loss (Ap), the dimensions and properties of a pipeline

(d, k and L), and the flow velocity (u): It can also be

derived by dimensional analysis, ie. Ap = f.(p,u,/J,L#A,S)

where; p is the density of the flowing fluid, u is the

linear velocity of flow, v is the viscosity of the fluid,

L the length of the "pipe", A the cross sectional area

and S the wetted perimeter of the pipe.

Removing L and S from the right hand side of the

equation, allows it to be expressed as:

AP/LS = f(p,u,(JrA) (2.3)

Assuming a polynomial solution, ie. raising the unknown

parameters to the powers a, fif y, and X. respectively,

leads to Atkinson's solution where R, the specfic

resistance is given by

„ kLS R = ~ T (2.4)

A

with ot = fir/2*, (from the dimensional solution) ; L being

path length and S perimeter.

Figure 2.1 shows the relationship between the coefficient

of friction (k) and Reynolds number (R) for fluids moving

in pipes, with the linear k values plotted against the

log10 values of R, as given by Skochinsky and Komarov

(64). For Reynolds' numbers below 2,000 Fig 2.1 shows that

laminar flow regime applies, and k=64/R. Beyond the

transition zone, with Reynolds' numbers typically above

100,000 the dimensionless friction factor becomes

constant for various roughness "pipes". in most mining

situations Reynolds' number, given by eqn (2.5) is

usually greater than this value.

« = ^ (2-5)

where symbols retain their defined meaning, and v

represents the dynamic viscosity.

The values of n marked on the curves in Fig 2.1 are given

by n = £/r, where c is the absolute roughness measured by

the mean value of the projections from the walls of the

pipeline and r is the radius of the pipe.

k

7A

M O O

O

1.0

0.8

0.6

OJt

0.2

\

\ \

V

n= 1066

ti* 0.0326

••• nz

i rl

n

0.015.1

.0081

.O.OO'i

0L — 2.6 3.0 3A 3,8 4.2 0.6 5.0 5.4

log Reynolds' Number

Fig 2.1: Friction Factor as a function of Reynolds' number with relative roughness as a parameter after

Skochinsky and Komarov (64).

8

The foregoing equations allow the calculation of energy

requirements based on experimentally determined friction

factors. Energy requirements, particularly the head loss

in the flowing fluid allow for the correct selection of

fans and forward planning determinations in overall

network designs.

Design of the ventilating system networks has been

greatly enhanced with the development of the digital

computer. Programs have been developed which allow input

of the various network parameters and the output of

information on the expected airflow performance with

various fans.

These programs involve an application of network theory,

combined with Atkinson's equation and, in general, use a

Hardy-Cross style iteration to reach a solution.

The fundamental relationships governing the flow about

the network are conservation of mass and energy.

Conservation of mass is maintained for the network by

ensuring that the sum of flows at a node is zero.

Equation (2.6) after Hartman (63) represents this

situation.

9

n

j=l

Qj = 0 (2.6)

Ensuring the total sum of pressure drops around all the

loops in the network is zero means that energy is

conserved. Equation (2.7) is formulated for each loop. An

iterative approach (63) is then required to reach a

solution.

m n

j=l i=l

A P i f j = 0 (2.7)

where Ap is the pressure drop for the ith branch of •••»]

the jth loop, with m total loops and n branches for each

loop.

The digital computer is ideal for solution of the set of

simultaneous equations developed in a network program. As

a general guide, these programs accept as input the drive

and fan specifications, and output tabulated information

on the amounts of air flowing through the network with

expected pressure drops.

To determine the resistance values for the various

drivages modelled, "standard" resistance factors are

used. Table 2.1 presents typical values of resistance

selected for various roadway types.

10

The values tabulated below provide the starting point for

the estimation of the most appropriate resistance values

to use in any network being modelled. Additional

information is determined for specific driveages

determining the pressure drop and airflow, to allow

calculation of specific "k" values for use.

Rearranging eqn (2.1), and expanding for R, gives:

k = A3AP

Q2SL (2.8)

Where the right hand side terms of eqn (2.8) are

determined at strategic locations underground.

TABLE 2.1 Coefficeint of Friction - k (65)

DESCRIPTION VALUE

Smooth concrete lined all around

Concrete slabs or other lagging between arch sets

Concrete slabs or timber lagging between arch sets to spring

Lagging behind arches -straight airways

Rough conditions with irregular roof floor and sides

0.0037

0.0074

0.0093

0.0121

0.0158

11

With k values selected, the network is modelled and

"tuned" to ensure that computed results are consistent

with observations.

A solution of the 2 Drilling level (2 Drill) ventilation

network at the Elura mine has been made using a network

program run on a Sperry, 64OK personal computer.

2.2 DISPERSION MECHANICS: IDEAL FLOW

Air may flow in underground mine workings with varying

extents of mixing on a molecular level and also on a

macroscopic level, which is the result of the different

flow paths of air within the mine workings.

The two contributions are independent of each other in

that definition of a state of macromixing does not, for

example, define a corresponding level of micromixing.

Extreme limits of mixing, ie. perfect mixing and no

mixing at all (or plug flow) define corresponding ideal

flow behaviours. These two flow patterns are most

conveniently characterised by considering the time

required for each volume element of air to traverse a

given length of the flow path. For ideal plug flow the

time is the same for each volume element, whilst for

5\

12

ideal mixed flow there is an exponential relationship of

these times. The mean residence time t is given by:

t = £ (2.9)

where: L is the path length traversed, and

u is the velocity of the flow

then for ideal plug flow the exit time (age) distribution

Et is:

Et = cS(t-tQ) =00 at t = t (2.10)

6(t-t ) = 0 elsewhere

and for ideal mixed flow:

E = ~ e t/t (2.11) r t

Equation (2.11) defines the exit age (Et) or residence

time distribution (RTD) for ideal mixed flow. In real

systems, the distribution of residence times may arise as

a result of micromixing and macromixing, or as a result

of radial velocity distribution of the flow.

Since it is difficult to define a measure for quantities

such as the degree of mixing or, indeed, to make

measurements on the hydrodynamic state of the internal

13

flow in engineering systems, extensive use has been made

of models that describe the observable behaviour in terms

of external measurements.

The most widely used method of measurement is a

stimulus-response method, employing an appropriate tracer

substance. The introduction of the tracer is most simply

performed by way of a pulse, but other methods such as

step or periodic introduction can also be used. It should

be noted that measurements of RTD by any method cannot

define micromixing.

In spite of this limitation, RTD is most valuable as it

provides as much information on the state of mixing as

can be obtained short of measurement on the microscopic

level.

2.2.1 Ideal Mixed Flow Model

Consider a flow compartment of volume V, through which

air flows at a steady volumetric flow rate v. At t=0, a

pulse of tracer <5 (t) is introduced at the inlet. By

definition, the concentration of the inlet tracer is

uniformly distributed within the compartment. Let this

concentration (C0) be equal to unity. The exit

concentration C is then obtained by solving the material

balance equation, viz:

14

CQV <5(t) = CV +~AJ!~L (2.12) dt

dividing by V, and noting that C =1 o

c ... C dC <5(t) = f + — (2.13) t dt

integrating:

C = i et <5(t)dt (2.14)

Using the property of the Dirac-6 function

f(x)6(X)dx = f(0) (2.15)

the resultant solution is given in eqn (2.16) which is

the result for E. given in eqn. (2.11) since C was made w o

equal to unity in the above derivation:

1 -t/t C = -e (2.16)

t

2.2.2 Ideal Plug Flow Model

The derivation is most conveniently performed by

considering a step function input (F) and then

differentiating the resultant equation to obtain the Ee

and Etexpressions, where EQ is the dimensionless exit age

distribution.

15

Consider a differential length, dz, of a cylindrical

conduit, as shown in Fig 2.2. Fluid with a uniform

velocity u in the axial direction is passing through the

differential volume Adz, where A is the cross section of

the tube. At a time t = 0, a step input of tracer is

introduced uniformly across the cross section at the

entrance to the tube at concentration CQ. The general

unsteady state mass balance for the differential volume

can be written as:

input - output = accumulation (2.17)

where

tracer input = uCA

tracer output = uA (C + -=—• . dz)

dC tracer accumulation = A dz TT

dt Equating the terms,

uCA - uA(C + |f.dz) =Adz| (2.18)

or

with the initial boundary conditions

t>0, z = 0, C = C max

t = 0, Z > 0 , C = 0

t = o, z < o, c = cmax

15A

Fig 2.2: Plug flow model.

u_

1.0 (t/t) = 0

Fig 2.3: Step function response.

16

The solution of eqn (2.19) for the tracer concentration

at the exit (z = L) is:

C = 0, t < £ (2.20)

C = C , t > -o' u

which is a step function response F(t) as shown in Fig.

2.3.

The equivalent E. response is given by eqn (2.10) and is

simply a Dirac 6 function of unit area and zero width at

t = £ ^ u*

The specific mixing assumptions involved in this model

are the absence of mixing in the axial direction, and

uniformity of concentration and velocity in the radial

direction.

2.2.3 Pure Convection Model

For laminar flow in pipes and also for short pipes at

high flow rates, molecular diffusion would not have

enough time to act - so all that needs to be considered

as causing a spread of residence times is the velocity

profile.

The model that considers this siutation is the pure

convection model. To derive the mixing model for laminar

17

flow, one starts with a definition of the velocity

profile (66), viz:

»<v-S[-R)] (2.21)

where R is the radius of the tube, o ' r is the radial position at which the velocity,

u(r ) is determined, and

v is the volumetric flow rate.

For length L of tubing, the residence time t(r ) P

corresponding to u(r ) is:

t(r ) = u(r ) v p'

(2.22)

and the average residence time is given by

u (2.23)

where u is the average velocity u = v rcR o J

Solving eqns (2.21) and (2.22) for r gives: hr

18

Now (66):

c J P 2u[ 1 - (r /R )2lc.27rr dr *<*> = § = L P ° J (2.25)

o r

r p -•J u C 2 ^ r dr o p p or:

*C 1 f/l-t/t r 2l

F(t) = 1 J K ^ w J 2"rPdrP <2-26)

o o

Evaluation leads to

t2

F(t) = 1 - (2.27) 4t

and the exit age distribution is

E ssm. = £ (2.28) dt 2t

A comparison of the laminar flow residence time

distribution with corresponding plug flow and perfect

mixing results is shown in Fig 2.4.

It may be of interest to note that the mixing model for

laminar flow is similar to that for plug flow, except for

the radial dependence of velocity.

i\

18A

1.0

0.8

0.6

0.4

0.2

0

I . Laminar

— flow

— \/y

i \

Perfect mixing

I I I I I

—

—

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

(t/t) =0

Fig 2.4: Comparison of plug flow, perfect mixing and laminar flow residence time distributions

after Butt (66)

19

This is made clear when it is considered that the analog

of eqn (2.19) is:

d c ( rP) dC

~U(rp)— = dt (2-29) dz

2.3 DISPERSION MECHANICS: NON-IDEAL FLOW

2.3.1 Dispersion Model

Departure from the ideals of plug flow is treated by the

dispersion model which is of wide generality and

applicability. This model considers plug flow of a fluid,

on top of which is superimposed some degree of backmixing

or intermixing, the magnitude of which is independent of

position along the flow path.

Considering the one-dimensional dispersion model,

illustrated in Fig 2.5, the mass balance around the

differential length dz is:

in: convection: uCA

j• • ~dC

dispersion: -D-r— . A dC

out: convection: u ( C + ^.dz ) A dz ' dispersion: -D [ |£ + S-( g ]dz]

dC accumulation: ^ . Adz

dt

19A

— • -

— > > -

u — ^

©— ^ z >-

B H dz

—*- u

—© -«

>-

•_

At(T): uCA+(-D ^ + i L - A )

dC

dz dz

At(T): u(C + —-dz) A + v-/ dz

D dC+_d_ d c . d z

dz dz dz

A = cross-sectional area

A

Fig 2.5: One dimensional dispersion model

20

Equating the difference in input/output terms to

accumulation in the volume element gives:

d c ^ dC J d dt ' d z = "ud£ • d z + D^(dCdz)dz (2.30)

which on rearrangement becomes

n <=l£ „ dC dC D dz2 "

U di = dt (2-31)

D, the axial diffusion (or dispersion) coefficient, is

the parameter employed to describe the deviations from

ideal flow. If u is taken to be constant in the radial

direction, the rightmost terms in eqn (2.30) constitute 2

the plug flow mixing model (eqn 2.19) and D(^-£ j

Fickian form of diffusional correction term

a dz"

Using the model to produce F(t) and Et responses the

equation is solved (noting that the equation is no longer

in the form of an initial value problem, but a boundary

value problem) by making a change of variable. Let v

represent the position of the moving interface

represented by all elements of fluid introduced into the

reactor at some given time. in terms of the length

variable, this transformation is:

v = z - ut (2.32)

21

Substituting for z in terms of v gives;

d C dC

dv dt (2.33)

The boundary conditions for a step function in inlet

concentration of tracer are:

C = 0

C = 1

C = 0

C = 1

(V > 0, t = 0)

(V < 0, t = 0)

(V = oo, t > 0)

(V = -oo, t > 0)

(2.34)

The corresponding solution (66) is

C = i 2

1 - erf L 2/5T J

where

erf(y) =

/ *

exp(-v )dv J O

(2.35)

and is again a tabulated function. The F(t) response

computed from the one-dimensional dispersion model is,

then,

F(t) = \ - \ erf L - ut

2/DlT . (2.36)

i.

22

Rewriting in terms Of dimensionless time, © = t/t:

F(e) = I - I erf l - e 2 /©(D/uL).

(2.37)

Since E(©) = dF(©)/d© and Efc = dFfc/dt, then on

differentiation of eqn (2.37) and for small extents of

dispersion we obtain:

E(©) = — - exp

27 n(D/uL)

_ (1-Q)2

4(D/uL) (2.38)

The presentation of the one dimensional dispersion model

so far has been a modification of the plug-flow model.

Hence, u is treated as uniform across the tubular cross

section. In fact, the general form of the model can be

applied to numerous instances when this is not so, in

which case the dispersion coefficient D becomes a

parameter describing the net effect of a number of

different phenomena. Taylor (67) has illustrated the

effect on the combined contributions of the velocity

profile and molecular diffusion to the residence-time

distribution for laminar flow in a tube. The situation

considered is illustrated in Fig 2.6. For moderate flow

velocities the dispersion of a tracer in laminar flow

will occur by axial and radial diffusion from the flow

front and, in the absence of eddy motion, this will be

22A

r Dr

u(r| ™

Fig 2.6: Convective and molecular diffusion contributions to dispersion

23

via a molecular diffusion mechanism. However, the net

contribuiton of diffusion in the axial direction can be

taken as small in comparison to the contribution of the

flow velocity profile. This leaves one with a

two-dimensional problem, diffusion in the radial

direction and convection in the longitudinal direction.

Following the procedures outlined for eqn (2.31), the

following can be derived (66):

dc n f dZC l ac 1 , , ac

at = Du[ ^ + r *x J ~ u ( r ) !ir (2'39>

where DM is the molecular diffusivity for the tracer and

u(r) represents the laminar flow velocity profile. Now

eqn (2.39) is a nonsteady-state partial differential

equation, the solution of which under the best of

circumstances is going to be a demanding task.

Taylor (67) presents a rational approximation to this

solution in:

<?C a2 c dc m m — m

_ = D _ u _ _ ( 2 . 4 0 )

«Z

where C is a mean radial concentration, u the average

velocity independent of r, and D an effective dispersion

coefficient. In terms of the parameters of eqn (2.34), D

is given by:

24

2-2

D « ^gg- (2.41) 171

where R is the tubular radius. Of course, this

representation is valid only under the conditions stated,

with molecular diffusion in the axial direction being

negligible. Taylor (67) further showed that, for this

condition to exist, it was necessary that:

* | - » ] p » 6 . 9 (2.42) m

Note in the inequality (2.42) that the quantity (uR/D )

can be considered an axial Peclet number. The right-hand

bound of 6.9 has been criticized by Ananthakrishnan et

al. (68) as not being sufficiently conservative. They

propose that (uR/D ) > 50 should be used as a criterion

for the use of the one dimensional approximation.

For large deviations from plug flow and open vessel

boundary conditions - the only physical criterion where

the analytical expression for E& can be derived, the

resultant expression is (69):

Ee = , exP y An(D/uL)e

(l-e)2

4e(D/uL) (2.43)

V

25

Equations (2.38) and (2.43) are easy to solve as they

represent normal or Gaussian curves with mean and

variance:

t © = — = 1 (2.44)

2

°© = ~?~r = 2(D/uL) (2.45) (t)Z

for small extents of dispersion of eqn (2.38) and

en = Z 2 = 1 + 2(D/UL) (2.46) t

and 2

J* O ~,~/T* „,„,,, 2 *€> = - 2

(t) = 2(D/UL) + 8(D/uL) (2.47)

for the larger extents of dispersion of eqn (2.43).

Examples of F0 and E& computed from eqns (2.38) and

(2.43) are shown in Fig 2.7.

It may be useful to note that the property of additivity

of variances applies for flow through a series of flow

regimes, provided they obey the condition of

independence. The latter simply means that the fluid

loses its memory as it passes from region to region. The

additivity of mean times does not require this

independence of regions. So:

i

A

25A

0 0.5 1.0 1.6 1.8

Fig 2.7: FQ and EQ curves as calculated from eqns (2.28)

and (2.43) for different values of n [s (D/uL)-±] after Butt (66).

a

26

2 7 2

and

^at =1\ (2-49)

It is also noted that the term D/uL in eqns (2.37) to

(2.47) is not the reciprocal of the Peclet number. This

mistake is often made in the literature. In the Peclet

number (uL/D), D is molecular diffusivity, and even if

this D is taken to be the eddy diffusivity the answer is

still incorrect. The diffusivity (D) in eqns (2.37) to

(2.47) is a new and different diffusivity which

characterises the movement of fluid by longitudinal

dispersion, ie fluid overtaking caused by all possible

simultaneous effects such as molecular diffusion,

velocity differences, turbulent eddies etc.

The term D/uL then compares movement by the combined

dispersion referred to above and movement by bulk flow.

The dispersion number (D/uL) is related to intensity of

dispersion and geometric factor by the following

equation.

(D/ ) = (D/Ud)(d/L) (2.50)

27

The intensity of dispersion as measured by D/ud has been

found to correlate well with the properties of the flow

and the fluid, ie Schmidt's and Reynolds' numbers, where

the former is defined as:

sc= J5D~ (2.51)

and the latter by eqn (2.5)

For a given fluid Sc is virtually constant over a wide

range of temperatures. Its value for air is 0.71.

The relationship between intensity of dispersion and K in

pipes is given in Fig 2.8. It is clear from Fig 2.8 that

for turbulent flow D/ud is independent of Schmidt's 5

number and for K > 10 its decrease is also slight.

By inspection of Fig 2.8 it is seen that the behaviour is

analogous to that of k vs K in Fig 2.1. In fact, the

analogy between fluid dispersion and fluid friction

becomes even more obvious if it is noted that from eqn

(2.2) the pressure loss (Ap) is:

AP « f(^) (2.52)

Since at constant K, friction factor (k) is constant at

any position in the pipe then it is obvious from eqn

27A

io4

Re = dtup/n

Fig 2.8: Intensity of dispersion as a function of Reynolds' number for different Schmidt

numbers after Levenspiel (69).

28

(2.52) that Ap will change with L/d. Similarly, since at

constant K, intensity of dispersion D/ud is constant at

any position in the pipe so it is obvious from eqn (2.50)

that the dispersion number D/uL will change with d/L

only. In other words, Ap and D/uL represent effects

which are additive with flow distance. Moreover, as the

pipe length increases the pressure loss also increases

but the dispersion number decreases, meaning that, for

example, a burst of a concentrated gas will progressively

loose its identity with distance downstream.

The above conclusion, of course, is not new in the sense

that it confirms observed effects in everyday practice.

However, the dispersion mechanics theory and its

resultant equations and relationships allow the

dispersion to be quantified more rationally, and to draw

conclusions of the effect of operating variables on the

actual dispersion and not just that caused by molecular

diffusion. The theory shows that for flow in the laminar

regime the dispersion coefficient (D) is proportionial to ,2 2.

d u and inversely proportional to DM (eqn (2.41) and Fig

2.8). In turbulent regimes (K > 10 ), on the other hand,

D is essentially directly proportional to ud, is

independent of DM but is affected by the physical

properties of the fluid to a small extent viz (u/p)

In the intermediate flow regime as Fig 2.8 shows, the

effect of ud on D is between (ud)~ and (ud) .

29

Additionally the effect of key operating variables on the

spread of residence times can be obtained by solving

simultaneously eqns (2.9) and (2.45). The resultant

relationship is:

a = / D^ (2.53) u

Noting that residence time distribution (E. ) and

concentration of a tracer-like substance introduced into

the flow are related, then eqn (2.53) gives directly the

spread of concentrations also. Thus, for example,

doubling the distance will increase the spread by a

factor of y 2 whereas doubling the velocity will decrease

it very markedly, in fact, by a factor ~. „ o

of/§. The relationship between maximum concentration of the

substance and flow parameters including distance is

readily calculated from the value of the spread {cr) once

it has been evaluated from eqn(2.53). Of course, given

the relationship of eqn (2.53), maximum concentrations

may also be predicted and the resultant values used to

assess whether the required standards are satisfied.

Two, at first sight curious corollaries of dispersion

mechanics theory are that:

i) for a given length of pipe the dispersion number

(D/uL) remains constant at high Reynold's

numbers and is independent of the flow velocity,

and

a

30

ii) if the fluid is subjected to local mixing then

the more often this occurs along the flow path

the less mixed or dispersed will the fluid be

at the end.

The first result is explained directly by Fig 2.8 and the

second result by the equivalence between the dispersion

model of this section and the tanks-in-series models

(69), viz

cf\ = 2 (D/uL) = | (2.54)

where N is the number of mixing tanks along the pipe

length considered.

It should be noted that Taylor's theory (67), which is

the basis of Dispersion Mechanics, has been applied to

studies of the dispersion of dust and toxic gas pulses in

mine working, as well as the dispersion of blasting fumes

and Methane (70-74). The prime objective of these studies

was to evaluate the dilution of the substances involved

and not to characterise the dispersion behaviour of the

ventilating air itself. Additionally, dispersion studies

in mines reported in the literature (75-81) have involved

essentially the mathematical models based on Taylor's

(67) convection-diffusion equations for essentially

straight flow conditions.

31

2.3.2 Multiparameter Models

The flow models considered so far are incapable of

dealing with complex flow behaviour induced by

channeling, by-passing, combining or branching of the

flows, recirculation as well as the presence of dead

volumes in the flow path. Combining and branching of the

air flows are self explanatory and a feature that is

inherent in all underground ventilation networks.

In channeling a path of least resistance in the network

exists such that some portion of the fluid passes through

the channel. In by-passing a significant amount of fluid

enjoys a much abbreviated residence time in some part(s)

of the network whereas dead volumes indicate regions of

stagnation in which there is no significant fluid motion.

In recirculation the fluid travels back before turning

again. This type of behaviour may occur with slow moving

fluid in short, wide vessels. Fig 2.9 illustrates the

tracer response curves for these situations.

Derivation of the appropriate dispersion function for

such models is not difficult, since they essentially

consist of assemblies of components of dispersion models

considered earlier.

31A

Expccled

( (a)

r

Inlornal recirculation

Parallel paths

i>-t

Fig 2.9: An example of tracer response curves for fluid flow behaviour in equipment after

Levenspiel (69).

32

Stagnant or dead volumes in the flow path are evaluated

from the difference between the calculated and measured

mean times, that is:

vf _ vlot tmeas = ~u~~ Z ^calc = u (2.54)

therefore with VT = Vf + Vd

(t . - t ) V d

t , v, caLc t

(2.55)

The response in Fig 2.9 showing tracer appearing later

than expected has three possible explanations: an error

in flow rate measurement, an error in volume available

for fluid; or the tracer is adsorbed and held back on the

surfaces of the "pipe" being traversed.

Parallel flow parameters are evaluated from the

consideration of the areas under the curves and the mean

time of each curve. Figure 2.10 shows the output trace

(E. ) generated by an idealised parallel flow regime.

This system can be quantified by noting:

Ai + A 2 = 1

V l V 2 V~ = Ai v~ = V a n d ' (2-56)

32A

0 Y V, v V, fi = — -J Q - ' '; 01 v, Y Q*--2V

Fig 2.10: An idealized response curve for parallel flow.

33

The over all mean time is given by

[ V* + Va ]

Figure 2.11 shows an idealized output trace (E. ) of a

recirculating flow. In this case the areas of consecutive

curves decrease in a geometric progression whilst their

mean time increases in an arithmetic progression. The

total area of the curve must, by definition, equal unity.

From the measured values of either a or b, the

recirculation ratio of the system can be calculated, ie.

R a ~ R+l

(2.57)

In eqn (2.57) the recirculation ratio (R) is defined as:

volume of fluid returned volume of fluid leaving

Because of other flow complexities that may be associated

with recirculation it is best to use both expressions in

eqn (2.57) to check for consistency of R. If two

different values of R are obtained, then this suggests

the presence of dead volume regions in the system.

33A

(R + 1)

a>

a = R/(R + 1) b = 1/(R+1)

I N

- - Area = 1 - -" ^

b . 2b 36

k -Area = 6

v /-Area = ab

tf* Area = a2b

b lb 3b

Fig 2.11: Idealized response curves to step and pulse inputs for a recirculating flow after Levenspiel (69).

34

2.3.3 Tracer Introduction and Measurement

There are many ways of introducing the tracer into a flow

stream and measuring the response. There are also strict

boundary conditions in the derivation of the mathematical

expressions for Et - the residence time distribution. In

addition to the open vessel boundary conditions of eqn

(2.43) which allowed the analytical expression to be

evaluated, there are also closed vessel boundary

conditions as well as a number of others in between these

two extremes.

The analytical expressions derived in the previous

sections were based on the assumption that the pulse is

injected across the flow in zero time in such a way that

injection is proportional to the flow rate.

If the velocity profile of the flow is flat then, in

principle, injection uniformly across the cross section

should be easier to achieve than if the velocity profile

is not flat as, for example in the case of pure

convection in Sect 2.2.3.

Assuming that correct injection is experimentally

possible the analysis still requires that the tracer used

must also be a correct tracer. This means a tracer which

is in all respects indistinguishable from the flowing

*T*

35

fluid, ie. it has the same physical properties as the

flowing fluid. The best tracer would be a radioactive

isotope of the fluid and the best tracer input and

measurement would be the so called "Mixing Cup"

measurement, where the entire flow is collected and

analysed continuously.

Although fine in principle, the experimental difficulties

of even approximating these requirements in practice, let

alone achieving them, are immense especially in large

conduits such as mine roadways. Of the foregoing

problems, viz tracer and its introduction and

measurement, the more important requirement is to ensure

that the tracer is not too different from the flowing

fluid particularly with respect to the density. If this

requirement is satisfied then non-ideal introduction and

measurement will give a response curve which, with proper

flow modelling, and the right mathematical manipulation,

may give the proper Et curve.

2

If, for example, a non-ideal pulse of known cr , has been

injected then as shown by Aris (82), the relationship:

. 2 A(y& = - 2 = 2 (D/UL) (2.58)

(At)2

applies for any kind of input and boundary conditions.

36

If the tracer is introduced in a local volume element of

the flow and not fully across the flow cross section then

analysis of the previous sections would be valid for the

"flow tube" involved, provided the contribution of

molecular diffusion in the radial direction is small by

comparison with the dispersion in the axial direction,

(see Fig 2.6). This situation is practically ensured at

all but very low Reynolds' numbers. For these conditions

this would also give the dispersion characteristics

(D/uL) for the pipe as a whole. This follows from the

fact that what is being measured is a sample of the full

flow and as noted earlier, at high Reynold's numbers,

(D/uL) is a flow independent constant when the velocity

varies.

Moreover, one of the advantages of point introduction and

measurement is that any local anomalies in the flow

pattern can be detected immediately. Although

theoretically this would also be possible with a full

cross-section pulse, real response curves obtained in

actual practice are always "noisy" and it is often

difficult to distinguish with certainty which is the

noise and which is the flow anomaly.

37

2.4 UNDERGROUND TRACER EXPERIMENTS: LITERATURE DATA

In the work of Higgins and Shuttleworth (2) both pulse

and step input of N20 tracer were used. Fig 2.12 details

the section of the heading investigated and Fig 2.13

gives their results at position C. The authors state that

with regard to Fig 2.13

"the two curves are the results of two identical

experiments on different days and that on both days

work was in progress in the heading while the

experiments were being carried out and the positions

of the tubs, drilling rigs etc. were constantly

changing", and that

"The effect of these changes upon the longitudinal

dispersion of the Nitrous Oxide in the airstrearn can

be seen in the marked difference in the shapes of

the curves".

The above conclusion is important as it highlights the

variability of the results under actual mining conditions

even when every attempt is made to' keep everything

constant. It is of interest to note the use of the term

longitddinal dispersion which is, of course, the basis of

the Dispersion Mechanics theory that at that time was

still in its infancy and was not considered by the

authors.

37A

—63 )n -*-• Bm •»-

PNESSUUE TAPPINGS AT OIWICE PLATE

NzO 1HJECTION P01UT

Fig 2.12: Test layout of Higgins and Shuttleworth (2).

B i6 ?A 32 TIME. MINUTES (Nj 0 OH AT I MIN.)

-10

Fig 2.13: Reported tracer response curves (2) for the layout in Fig 2.12.

38

If the curves in Fig 2.13 are analysed by the methods

given earlier the following is obtained:

t = 5.65 min t, = 6.42 min 1 2

(D/uL)± = 0.104 (D/uL)2 = 0.079

The difference of some 20% in the mean times and the

difference of about 30% in D/uL values may indeed be

regarded as marked differences in the simple straight

section of Fig 2.12. From theory D/uL should be the same

in both cases and since airflow rate and the dimensions

were the same in each case then it must be concluded that

the dispersion coefficient must have been different in

the two cases. The above conclusion therefore means that

mining activity and the movement of machinery in the

various nearbye roadways, stopes, etc. has an effect on

the dispersion coefficient. In other words, the

dispersion coefficient in working mines cannot be assumed

to have a constant value.

Tracer response curves of Higgins and Shuttleworth (2) at

different positions and distances from the face are shown

in Fig 2.14, and in their E. form, calculated by the

analog of eqn (2.38), are shown in Fig 2.15.

38A

3 6 9 12 TIME, MINUTES (N2O ON AT I MIN.)

Fig 2.14: Face response curves of Higgins and Shuttleworth (2).

1,5

1.0 —

0,5

0,0

0 100

15 metres, X 15 metres, Y

26 metres, Y

28 metres, X

1 T 200 300 400 500 600

Time (seconds)

Fig 2.15: Calculated E. curves of the data in Fig 2

39

Using the calculating procedures outlined in previous

sections gives at the 15 metre position:

tx = 1.9min (D/uL)x = 0.08

t = 3.2min (D/UL) =0.45

and at the 26 metre position:

tx = 5.8min (D/uL)x = 0.31

t = 4.1rnin (D/uL) =0.45 y \ / /y

By inspection of Fig 2.14 and Fig 2.15 it is obvious that

the break-through time cannot be identical for all cases

as is incorrectly shown in the original plot (Fig 2.14).

The mean time for each duct distance is very different

but the expected lengthening of the mean time in direct

proportion to distance is reasonably satisfied.

The most significant feature of the above results is the

large difference in the D/uL values at the 15 metre

position for the X and Y positions, and their reversal at

the 26 metre distance.

This indicates that the dispersion characteristics across

the cross section of headings may be different and also

be a function of the distance. Another possibility is

that the tracer used may have preferentially segregated

\

40

in the heading. Since the density of N„0 is 65% higher

than that of air, this possibility cannot be discounted

even though the authors suggest in their paper that this

effect was not significant. It is unfortunate that no

results are given for the other three sampling positions

shown in the insert in Fig 2.14, since they would help to

decide in favour of one or the other effect.

In the USBM series of investigations (3-6), which began

some 20 years later, the tracer employed was SF , which

is more than nine times heavier than air, so it becomes

questionable whether the dispersion mechanics theory of

Section 2.3.1 should be used. It is of interest to note

that in their first report Thimons and Kissell (3) found

"the major problem to be incomplete mixing of the dense

SF^ with the mine air in airways of low velocity". They

note, however, that "at high velocities there was no

problem". These comments, of course, relate to the

injection stage, and no mention was made of segregation

which may have taken place downstream.

Thimons and Kissel (3) used pulse input typically by

releasing SFtf as a jet spray from a pressurized lecture

bottle whilst at the same time moving the lecture bottle

around the mine airway to further improve mixing.

41

By reference to Sect 2.3.3 this technique of tracer

release is far, far away from even approximate ideals of

pulse input. Thus, although application of dispersion

mechanics may be doubtful, in so far as the absolute

values are concerned, the results can still be used on a

comparative basis.

The response curve of an experiment made by these

investigators (3) in which SF^ was released at location R

and measured at location S in the mine of Fig 2.16 is

shown in Fig 2.17.

By inspection the overall shape of the response curve in

Fig 2.17 is reasonably normal but the initial portion,

except for an unexpected low C , is suggestive of

parallel flow (see Fig 2.9(e)).

Considering the physical situation of Fig 2.16 the only

possible true parallel paths are the three parallel

North-south headings. Under normal conditions, of course,

the response from these would be expected to show up in

the curve later. A probable explanation for the early

appearing parallel-like signal is that some

SF^-containing air leaked through the various stoppings

in the cut-throughs separating intake and return

headings. The leaked portion was then united with return

air ahead of the main portion of the SF signal.

41A

ununrX^ 2 bull L-ii—'

Exhaust­ion

I V)

>*

LEGEND

—*- Intake air

'—< Return air :(tT Door ~t~ Regulator " T ~ Curtain

Temporary stopping

.30

IZ}|ZZ Permanent stopping 7- Brallice

X Release location A Sampling location

Fig 2.16: Plan of the USBM experimental mine (3).

,000

BOO —

600

Ll.

in 400 —

200

10 20 30 . 40 50 60

TIME FROM RELEASE OF SF6, min 70 BO 90

Fig 2.17: Reported tracer response at position S in the mine of Fig 2.16.

42

The mean time of the initial signal in Fig 2.17 is

approximately 15 minutes, suggesting leakage through the

door rather than other ventilation structures. The mean

time of the main portion of the response curve,

calculated from the airflow and distances given in the

paper (3), is 35.7 minutes* The D/uL for the main portion

of the curve is calculated as 0.038, meaning that this is

the characterizing value of the spreading process of the

mine air and not of the SF . ©

An interesting recirculation experiment in a deep copper

mine cooling plant, reported by Thimons and Kissell (3)

gave the response shown in Fig 2.18. Using the procedure

outlined in Sect 2.3.2 and noting that the first signal

appears early, the calculated model and its parameters

are given in Fig 2.19

Thimons and Kissell (3) gave the following interpretation

of Fig 2.18:

"Approximately 50% of the air passing through these

cooling plants is recirculated" and "the individual

peaks most likely represent recirculation along

different paths."

These conclusions were obtained by the authors (3), in

part, by a correct consideration of the geometric series

\

42A

1,000

800-

.o Q.

a

600 -

I? (/> 400-

200

10 20 30 40 50 60 70 80 90 100 TIME FROM SF6 RELEASE, min

Fig 2.18: Response curve of Thimons and Kissell of a recirculating situation (3).

Y = 1/2 (DM)^ 0.021

T»l

V1

Fig 2.19: Calculated flow model for the response of Fig 2.18

43

(see Fig 2.11) and in part, by spurious reasoning, are

supported by the calculations based on dispersion

mechanics theory in Fig 2.19. It is also evident from Fig

2.19 that dispersion mechanics enables the recirculation

system involved to be specified quantitatively, but for

reasons noted earlier, only in relative terms in this

case. Nevertheless, this may still be considered useful

as it gives the ventilation engineer a good basis on

which to carry out rational improvements in the

ventilation system.

A true recirculation response obtained in ventilation

trials of a full-face Lovat tunnel boring machine (TBM)

and reported by Stokes an</stewart (7) is given in Fig

2.20. These workers used propane (CHD)) which was "pulse

injected" from a pressure bomb by a quick acting solenoid

valve. It is notable that Stokes and Stewart (7) treated

the 50% density difference between C H and air as "a

matter of concern" and went to elaborate lengths to test

conditions where the density effect would be

insignificant. It is clear from the foregoing quotation

that Stokes and Stewart (7) understood the need to employ

proper tracer substances. However, as with previous

investigators in the trials they did not analyse their

data in Fig 2.20 by the dispersion mechanics theory. If

this is done then the model corresponding to the tracer

response curve in Fig 2.2 0 is that shown in Fig 2.21.

43A

10

9

8

/

6

5

2 4 C 3

I

0

IHOECTION POINT * 1?

HEAD ROTATION : <l RPH

15 SECOHO PERIOD

1(1 00 00 100 120 140

EI-AP5E0-TIHE. 51HI.ETn/\CEIt RCtfASE (SECONDS)

160 100

Fig 2.20: Recirculation response curves of Stokes and Stewart (7).

T ^ 2/3 (D/uI^- 0.08

V=l

nr*

Fig 2.21: Calculated flow model for the response of Fig 2.20.

44

In Fig 2.21 an average value of D/uL is shown. This is

because D/uL of successive curves was not constant,

although it should be, but varied in the range 0.0041 to

0.0062. A possible explanation is that the curves in Fig

2.20 were not exact copies of the original. This

explanation is also supported by the fact that the second

and first pass, which was ignored in the calculation of

Fig 2.21, have the same Cwi„ value. MAX

2.5 SUMMARY

In summary, the use of tracer techniques to study aspects

of ventilation in mines has been shown to be possible.

The workers referred to above, have all been unanimous in

their conclusions that the method offers a possibility of

evaluating ventilation characteristics and phenomena that

cannot be done by traditional methods. Examples of these

were given by the USBM investigators (3-6), for both coal

and metal mines, and by Higgins and Shuttleworth (2) for

an NCB colliery. The latter investigators also concluded

that "if the time of release of the tracer has to be

limited, or there is significant longitudinal diffusion

the Pulse Release Method is preferable (to step input

methods)". It can also be added that the pulse release

method is more practical underground and is less prone to

noise masking.

45

Finally, none of the above investigators examined their

work in the light of Dispersion Mechanics theory. It is

not known why, at least in the later investigations, this

had not been attempted. As noted earlier, what appears to

have been the first attempt to do so had been done in a

small hydraulic model (26->28) . The details of the work

presented at the Illawarra Branch Symposium on Mine

Ventilation (9) and the Third International Mine

Ventilation Congress, Harrogate (1984) (10) generated

considerable interest amongst the delegates.

46

CHAPTER 3

EXPERIMENTAL INVESTIGATIONS

Trials were conducted on the release and detection of

tracer gas in the ventilating airflow underground at the

Elura Mine N.S.W. The following sections detail the

development of the experimental method used in the

conduct of trials.

The provisional methodology and measuring equipment were

tested prior to mine investigations. These tests were

designed to investigate and ensure that reliable results

could be obtained from equipment, and that it was robust

enough to withstand the underground environment.

The initial tests were conducted in the laboratory and

then on a larger scale rig prior to actual underground

measurements being made.

3.1 LABORATORY TESTS

Laboratory tests were conducted in the Department of

Civil and Mining Engineering laboratories at the

University of Wollongong. The principal purpose of the

laboratory tests was to determine a suitable tracer and a

suitable detection system for use in further experimental

work.

47

3.1.1 Tracer Selection and Detection

In Residence Time Distribution (RTD) studies it is a

requirement of the method (Sect 2.3.2) that the tracer

used has similar properties to the bulk gas. For

practical purposes it is also essential that the tracer

gas can be adequately injected and measured.

As noted in Sect 2.3.2, tracers used to date have not met

the first of these requirements.

A search of chemical literature (83) showed that the gas

which meets the above requirements for use in air is C H Z Z

(Acetylene).

Table 3.1 shows the properties of CH, and Air at STP. It

is obvious from this table that the properties of the two

gases are very similar.

TABLE 3.1 - PROPERTIES OF C R AND AIR 2 2

PROPERTY C H AIR 2 2

28.84

1.265

1.83

3.617

2.06

Molecular Weight

3

Density kg/m -5

Viscosity,kg/m.s(xl0 )

Molecular Diameter, nm

Molecular diffusivity,

m2/s (* 10~5)

26.05

1.163

1.79

4.232

1.73

48

Being a hydrocarbon a number of standard techniques are

available for C2H2 detection. These techniques include

gas chromatography, flame ionization methods, bi-metallic

powder and conductivity methods.

On the basis of cost, simplicity and sensitivity, as well

as its ability to be continuously measured, the

bi-metallic powder method was selected as being the most

practical technique.

3.1.2 Apparatus

The apparatus used consisted of the release and detection

equipment arranged as shown schematically in Fig 3.1.

Equipment used included:

Vacuum Pump Electrolux model number 81743. This pump was

used to draw atmosphere samples over the detector as

preliminary tests revealed that the through flow

resistance of the head was too high and measurements

were not reliable without suction assistance.

Chart Recorder - Houston Instruments OmniScribe. A two

(2) Channel recorder, with a 2 Volt full scale

48A

Overall Length 1600mm

Fan-y r Flow Streightener •Dia lfiOmm

H; Tracer input /

37 Cable

Suction Line

—

Chart Recorder

Fig 3.1: Line diagram of laboratory apparatus

49

maximum input and a maximum resolution of 1 mV full

scale. 23cm wide paper was used. The possible paper

speed ranges varied between 2.5 cm/hour and 25

cm/min.

Detector and Power Supply: The detector used was a Tandy

Moel BT, hand held bi-metallic breath alcohol

detector modified to suit continuous remote

recording. Figure 3.2 gives a circuit diagram of the

detector. Power supply to the head was provided by

using a 24 0V, 115Hz transformer stepping down to 3V

DC.

Physical connection to the vacuum pump was made by a

flexible suction line.

Input and output cables led, respectively, to the

power supply and the chart recorder.

Release System: The tracer gas (C2H2) was contained in a

pressurised cylinder at 12 0 bar. The gas was

released by momentarily opening the main feed valve

on the C H cylinder.

^

49A *'

Ext 6 V o —

..2757

6V

d>Dn -•ff 9 Test

$ 3.3k

XZ y

3.9k. •co .SO

o •X)

3.3k

# &

Dn VRH

( » - / M ^ /.©—

o> Teste?

c»-

5 6

•n p "J O 03

^

ru o

> VR1

4 10k

Fig 3.2: Circuit diagram of detector Tandy Electronics P/L.

50

3.1.3 Calibration of Equipment

All the equipment used during the course of the

experimental trials was calibrated to determine the

response from known inputs.

Vacuum Pump Calibration y

Figure 3.3 shows a plot of Pressure vs Flowrate for the

Electrolux Vacuum Pump. The plot was obtained

experimentally using a rotameter and pressure meter on

the inlet to the flexible vacuum line. The pressure

volume flow characteristics define the operation of the

unit.

To ensure effective response from the detector it was

found necessary to include a flow bypass. This was a

simple finger operated rotating collar over an opening in

the metal tube mounted on the rear of the detector (see

Fig 3.4).

Chart Recorder Calibration

The voltage response and the chart speed of the chart

recorder were calibrated.

50A

1.1 -

1.0 4

0.9 J

0.8 J

/~\

6 Q-X \s

(b L

0.7

0.6

0.5

3 0.4 in

L 0.3

Q_ 0.2

0.1

0.0 I I I I 1 I 1 I I I I I I I I 1 I I I I 1 I I M I I I I I I I I 1 1 1 I T T

0.0 1 0.1

I I I I I I I I I I I I I I I I I I 1 I I

0.2 0.3 0.4

Flowrate (n /sec)

Fig 3.3: Calibration curve of pressure vs volume for the vacuum pump.

50AA

-o o X o>

c o 2

Rotating Collar

To Vacuum Pump

J

Elevation (Not to Scale)

Fig 3.4: Rotating Collar flow control device

51

In the first instance known voltages were input into the

channel used for the detector. The response of the chart

recorder to these voltages was marked on the chart.

Table 3.2 gives a listing of the input and measured

voltages recorded during this test. To determine the

actual chart speed the chart was run for a known period

of time. This time period was determined by a stop watch.

Table 3.3 lists the speed settings tested and the

recorded time and distance values made during the

calibration trials. Averaged values taken from these

calibration trials were used in later interpretation of

results.

TABLE 3.2 - CHART RECORDER CALIBRATION RESULTS

INPUT VOLTAGE (Volts)

1 1 0.9 0.8 0.7 0.6 0.5 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0.05 0.05

SENSITIVITY (Marked)

1 V 2 V 1 V 1 V 1 V 1 V 1 V 500 500 500 500 200 200 100 100 50

mV mV mV mV mV mV mV mV mV

MEASURED VOLTAGE (Volts)

Off Scale 1.05 0.93 0.84 0.75 0.61 0.51 0.49 0.405 0.295 0.198 0.195 0.103 Off Scale 0.049 0.049

52

TABLE 3.3 - CHART RECORDER SPEEDS

INDICATED CHART SPEED MEASURED CHART SPEED

2.5 cm/min 5.0 10.0 12.5 20.0 25.0

2.4 cm/min 4.85 9.71 12.47 19.42 23.78

Detector Calibration

The detector was calibrated by introducing known

concentrations of a tracer/air mixture into a mixing

container and using the head to sample this mixture.

Figure 3.5 shows the layout of the equipment employed.

The response of the detector was approximately linear.

Figure 3.6 shows a plot of the results of measured

concentration (ie. chart recorder response) vs actual

concentration.

3.1.4 Laboratory Method

The method of employing the release and detection

equipment, shown in Fig 3.1 was developed through

repeated trials.

52A

KEY

Electrical Cable

Gas Flow

Tracer

Supply

Air

Supply

Mixing

Chamber

Chart

Recorder

A

Monitoring

Head

A

To Vacuum

Pump

Fig 3.5 Diagram of the setup used for detector calibration

52AA

0

nt i j i in 1111111111111 ri) 1111rn 111 ri in 1111)1111 ri i'

100 200 300 400 500

Input Concentration (ppm)

Fig 3.6: Detector mV response vs concentration plot

53

The method developed required the sequential performance

of the following:

- Switching on power to the detector. It was required

that the detector be powered up some five to ten

minutes prior to the commencement of testing. This

period allowed the head to "warm up" to give

consistent results.

- Starting the vacuum pump, at a reduced flow rate. The

vacuum pump was operated at an optimum flow rate of

25 cm /s to ensure the optimum reading on the

detector head. Flow rates above this level generated

inconsistent results and below this level

insufficient sample is drawn over the detector. The

reduced flow rate was achieved by using the bypass

arrangement on the intake line to the pump.

- Zeroing the chart recorder. A desired zero line

position is set using the zero set knob on the chart

recorder.

Setting the required sensitivity on the chart

recorder. Using the sensitivity switch the required

range is selected. For most of the laboratory trials

a 1 Volt range was used.

54

- Starting the chart recorder paper. A chart speed is

selected and the chart started. Nominal speeds

employed in the laboratory trials were 20 and 25 cm

per minute.

- Releasing the tracer gas. A short "burst" of gas was

released into the mouth of the perspex pipe using

the main control valve (see Fig 3.1).

- Shutting down the system. Once the trace had been fully

recorded (ie. the chart pen returns to its zero set

position) the equipment can be shut down, or

additional trials conducted.

This method was developed to allow for the consistent

detection of C2H tracer gas. Pulses of the tracer pass

along the perspex pipe and are detected at the detector

head. The output curves produced by the tracer gas are

concentration-time plots suitable for later analysis.

Figure 3.7 shows a typical example of the actual response

curve during initial trials.

3.2 LARGE SCALE PROVING TESTS

These were conducted using lengths of 900mm diameter

"Spirex" ventilation ducting, a compressed air auxilliary

fan and CH2 injection and measurement equipment as

54A

1 1 — j — • - . - — - T J —

Pi'INTED INALISTRAl

Fig 3.7: Typical response curve obtained in laboratory tests.

54AA

Figs 3.8 and 3.9: Surface test rig and Tracer Input Devices

55

described in Sect 3.1. A line diagram of the equipment

employed is shown in Fig 3.8.

Pressure tappings were made in the ducting as shown in

Fig 3.8 and these were connected to water manometers.

These were used to both measure the pressure drop and the

flow rates. The latter were calibrated using velocity

readings obtained with an anemometer. To test the

behaviour of point injection and that of the injection

across the cross-section two different injection devices

were used as shown in Fig 3.9. The procedure consisted

typically of switching on the air fan and setting the

flowrate at a predetermined value obtained by reference

to the calibration results between manometer (M2)

readings and the corresponding flowrate.

After the tracer measuring equipment had been prepared

according to the procedure in Sect 3.1.4, then for both

injection modes, the on-off valve on the CH2 cylinder

was momentarily hand activated, to release the tracer

into the airstream.

The above procedure was repeated at different airflow

rates and again with other different lengths of ducting.

The different lengths were made up by simply butting the

ends together and wrapping the join with ducting tape.

A

56

The required lengths of the ducting were inserted between

the intake and exit lengths which always remained in

place as they contained the injection and the measuring

devices. An example of the response curves recorded on

the chart recorder in these trials is shown in Fig 3.10.

3.3 UNDERGROUND STUDIES

With the methodology of the system proved in the

laboratory and on the large scale rig, the next step

required the adaptation of the experimental system for

use in the underground environment. In all 192 separate

runs were made underground at the Elura Mine (11).

3.3.1 Test Sites

Two sites were selected for the underground proving

studies.

The first site for preliminary trials was the 4 Drill

level entrance access (Refer Figure 3.11).

The second site was on the 2/8 North cross cut on the 2

Drill level. (Refer Fig 3.12 for a detailed plan.)

The 4 Drill site was selected for the simplicity of the

network in the area, and the flowrate of the ventilating

56/*

.._!...

J ! !

I : •• I • I

;-i L..t">...

Fig 3.10 Typical Response curve obtained in the large test rig

56AA

Fig 3.11: Plan of 4 Drill level

5 6 AAA

KEY 9 ConTBjor Belt Regulator

Grid Una (50x60) Pillar outline

"^>- Stoired mullock •topping (n> Looatlon of Slta n

Fig 3.12: 2 Drill Plan with test sites marked

i.

57

air along the driveage. At the time of testing, the 4

Drill level was acting as an exhaust airway, taking

polluted air from the Crusher/Loading station to the

upcasting exploration shaft.

The exploration shaft was fitted with a CY1615 Richardson

fan, expelling 95 m/s to atmosphere.

Changes in the mine production schedule required the

movement of production development to the 4 Drill level.

Trials were then continued on the 2 Drill level.

The 2/8 North cross cut offered a similar layout to the

straight driveage tested on the 4 Drill level, with the

added advantage of a regulator positioned at the exhaust

end of the drive. The conveyor belt regulator (see Figure

3.12) could be opened or closed to increase or decrease

the flowrate along the driveage. Photographs showing

typical driveage sections at the test site are presented

in Fig 3.13.

3.3.2 Equipment Usage

The equipment employed in the previous trials was

modified to suit the underground environment through a

number of refining steps.

57A

Fig 3.13 (a): Line of Backs, 2/8 Cross Cut

Fig 3.13 (b): View along drive, 2/8 Cross Cut

i

58

Initial underground trials conducted on the 4 Drill level

showed very unstable results. This instability was most

probably due to a number of contributing factors.

The lack of shielding between the detector and the chart

recorder, the instability of the chart recorder position

(mounted in the rear of the mobile vehicle) and the

proximity of the power generator to the chart recorder,

were the most significant factors.

To overcome these problems the chart recorder was moved

to a position remote from the mobile generator, and

plastic sheathed cables run from the detector to the

recorder.

All of these changes were made with the change of the

testing site to the 2 Drill level. Additionally a 25

metre single phase extension lead was connected to the

mobile generator allowing the chart recorder and

monitoring head to be set remote from the generator.

The detector was fitted with an intake evase to improve

the percentage of the available area sampled by the head.

This modification improved the detection of released

pulses of tracer gas.

59

Power supplied by the mobile generator in the 2/8 cross

cut location (Fig 3.12) required the nearby parking of

the underground vehicle. In the final location, (the

Western Vent Shaft access on the 2 Drill level) where

most of the results were obtained, this was undesirable,

as the airflow was interrupted about the vehicle.

To ensure consistent supply, a power line was run from a

distant sub-station transformer to the test site. This

provision alleviated the airflow problem and the need to

park the vehicle so close to the site. 240V, 115Hz supply

at a maximum of 10 amps was provided by the supply line.

The release system for the tracer gas was modified

through the course of testing. Initial release of gas

underground was made through the partial filling of a 20

litre plastic bag which was rapidly squeezed to expel the

tracer into the ventilating air stream.

Problems caused by inconsistent times for complete

expulsion of the tracer were noted.

After further experimentation with various alternatives

the system was upgraded to incorporate the use of

balloons, 2.5 litre capacity, which were filled and

punctured to release the tracer gas (C2H2) into the

ventilating air stream.

60

All main underground tests were conducted using balloons

for the release of tracer.

An equipment list for the tests in their final form

is:

Service vehicle for transport of equipment and power

generation. A Toyota 2.2 litre Diesel 4x4 Landrover.

Lighting: Two 1000 Watt, 240V AC sealed beam lights

operated as required.

Release system: C2H2 pressurised container, 120 Bar with

balloon filling nozzle fitted to main valve system.

Chart Recorder, Vacuum Pump, 240/3 V Transformer and

Detector as used in laboratory trials.

Consumables; balloons, chart paper and additional C2H2

cylinders.

Use of this equipment is detailed in section 3.3.3.

3.3.3 Test Method

Through trials conducted at the locations, detailed in

Sect 3.3.1, the optimum method of conducting the release

and detection tests was determined.

\

61

Prior to the commencement of release and detection tests,

"traditional" measurements of the airflow were taken. An

annemometer traverse was conducted in the roadways being

tested to determine the flowrate and velocity. Wet and

Dry temperatures and an Aneroid Barometer reading were

also taken. A repeat of these readings was made every two

hours during, and at the completion of testing.

A sequential list of actions required during the conduct

of a single test, after "traditional" values were

obtained, would include:

1) Transport all the equipment to the required location

and connect the power line to the established

monitoring site from the generator in the vehicle

(not required after the installation of the power

line to the West Vent Shaft location on the 2 Drill

level.) and set up (Fig 3.14).

2) Warm up the chart recorder and detector, switching the

main power supply on some five to ten minutes before

the first release. At the same time the chart span

(Fig 3.15) is zeroed.

3) Mark out the release points. The release areas were

marked out using reflective spray paint to ensure a

consistent release position was used. This work was

61A

-ar 1 r K li-.

¥* •

^UtfftaaaaB kaa^^^3l

Fig 3.14: West Vent Shaft detection site.

v;

T

1

^ *#/A

m Fig 3.15: In situ zeroing of the chart recorder.

62

considerably more involved in locations where

previous velocity profiles had been made. (Refer

Sect 3.4.2)

Additional markouts were made to allow for the

conduct of successive tests during a single session.

4) Inflate the balloons with the tracer (Fig 3.16) using

the touch valve on the cylinder (Fig 3.17). A number

of tracer balloons were prepared and stored

downstream from the detector awaiting release.

5) Record the run number, chart speed, sensitivity and

traditional ventilation details on the chart.

6) Release tracer and start chart recorder. A stopwatch

system was employed. The procedure was to first

start the chart drive on the recorder then walk to

the release location, release the tracer (Fig 3.18)

and start the watch at the instant the tracer was

released.

Leaving time for the tracer to move to the detector,

the release operator would then move to the chart

recorder position. The paper feed would be halted at

62A

Fig 3.17: Close up of tilt valve

62AA

Fig 3.18: Balloon in position and ready for release.

63

a given watch time. The elapsed time was then

marked on the chart to give the time of release.

The above procedure was particularly convenient at

release locations out of direct sight of the chart

recorder station. However, the shortcoming of the

procedure was that often the chosen mV span was not

large enough to record the full response curve, so

many runs had to be repeated at other spans to

obtain the full curves.

7) Repeat trials could be conducted by repeating steps

4,5 and 6.

3.4 ADDITIONAL WORK

Beyond the development of the testing procedure some

additional analysis was undertaken. This work defined

some of the performance characteristics of

equipment/systems used in the underground tests.

3.4.1 Balloon Release Characteristics

The use of balloons as a method of releasing tracer gas

into the ventilating air stream was developed after

unsuccessfully trying the bottle release (after Thimons

63A

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. J.luxiiu;lT t;_. x n l .1 TX:. ..nil ill 11.11 xixlr tmll..-.U . .11 Itlxi Fig 3.19: Recorder tracer of (a) balloon release and

(b) plastic bag release.

64

and Kisell (3)) and a plastic bag method referred to in

Sect 3.3.2.

A clear comparison of plastic bag and the balloon methods

of pulse release can be seen between the output traces

shown in Fig 3.19. These tests were made with a release

of gas from the same distance from the detector using the

two different methods. As can be seen from Fig 3.19, the

balloon release method shows a consistent rapid rise to

the maximum followed by a steady drop in concentration

after the maximum, whereas the response from the "plastic

bag" release shows a "bi-modal" response, the first peak

being due to irregular release.

To improve the clarity of interpretation of RTD results

it is desirable to have a consistent and reproducible

pulse shape. This was achieved using balloons.

Physical observation of the release characteristics of

the balloons was also made.

Balloons were partially filled with talcum powder prior

to the introduction of tracer. Agitating the balloons

prior to puncture ensured that the powder was "well

mixed" with the tracer gas. The balloon was then

punctured and the movement of the powder observed.

65

For any puncture position on the surface of the balloon

the tracer/powder appeared to form an ellipsoid along the

diameter punctured. Figure 3.20 shows a photograph of the

spread directly after the balloon was punctured.

Figures 3.21 and 3.22 are photographs from a series of

balloons burst in the same manner. For this sequence

photos were taken at differing distances from the burst

position.

Figure 3.23 shows a diagram of the ellipsoid formation

and movement during the conduct of a test.

The talcum powder "falls out" of suspension reasonably

quickly, but indications during the period where it was

well mixed with the tracer suggested that the air flow

may be laterally discrete.

3.4.2 Detector Evase

The final evase design shown in Fig 3.24 on site and

depicted in Fig 3.25, was the result of a number of test

runs on inlet shapes for the unit.

Initial trials on the 4 Drill level were conducted using

the head without any inlet control as was the case in

laboratory and large scale tests where the detector

k

65A

Fig 3.20: Balloon burst from below.

Fig 3-21: Balloon burst from below - 1 metre downstream

65AA

Fig 3.22: Balloon burst from below - 5 metres downstream.

1) Before buret 2) After buret

3) 6 metree from buret 4) 10 metree from buret

Fig 3.23: Diagram of observed tracer spread.

6 5 AAA

Fig 3.24: Cone evase on site in WVS regulator.

900

$ 375mm

pf 150mm

Elevation End Elevation

Fig 3.25: Evase Detail

66

performed well as such. In the underground situation,

however, this resulted in a poor relationship between

pulses released and detected.

Tests conducted in the 2/8 cross cut used a "box" evase1,

detailed in Fig 3.26. This system proved quite adeguate

in the relatively low flow rates (linear velocity less

than 1.0 m/s) along the 2/8 cross cut.

However, with a change of location to the West Vent Shaft

(WVS) position it was necessary to develop the final

system to overcome stability problems in the very high

flow velocities (up to 20.0 m/s). To this end, the mild

steel, rubber lined conical shape evase (Fig 3.24) was

employed. The weight and shape of this unit ensured its

stability and performance in the flow rates experienced

at the site.

3.4.3 2 Drill West Vent Shaft Monitor Position

A number of "lost pulses" (ie. tracer release trials

which were not detected at the detector) occuring in the

2/8 trials when the detector was located in the 2/8

drive, proved problematical.

66A

Elevation End Elevation

Fig 3.26: Box evas L

67

To overcome these problems a series of tests were

conducted with the monitoring head mounted in the

regulator in the access to the Western Vent Shaft of the

2 Drill level. Figure 3.27 shows a dimensioned drawing of

the head in the location with an inlet evase attached.

The size and shape of the inlet evase ensured that a much

greater percentage of the effective roadway area was

sampled. Previously tests had been dependent on the

detection by using a non-streamlined sampling head,

comprising 3% of the cross sectional area.

Tests made during the early portion of this testing

period showed a more consistent appearance at the

detector, with 7 from 9 pulses being recorded.

It was noted during testing that the release point of the

tracer had a considerable effect on the extent of

detection of the tracer gas.

Carrying on from the first successful trials with power

supplied from the sub-station line trials 55 to 64 were

conducted. Only one pulse was recorded from ten releases.

The only notable difference between the trials 46-54 and

55-64 was in the position of release.

67A

Elevation - Looking West (NTS)

Fig 3.27: Detector position, WVS

68

Figure 3.28 shows an expanded plan view of the area, with

the release positions marked. The positions on this plan

which were detected by the detector all coincided with a

similar position to that in which the monitor head was

located in the West Vent Shaft access.

3.4.4 Lateral Position Detection Trials

A series of trials were developed and conducted to define

the performance of the flowing air.

These trials involved a two part analysis of the flowing

air. Traditional analysis requires the use of an

anemometer traverse to provide an average flow velocity

value for a given driveage. To generate a closer focus

analysis of the airflow a velocity profile measurement

technique was developed, as discussed below.

A more defined positional release of tracer gas, at sites

for which the velocity profile was known was indicated.

The technique adopted for this work is also discussed

below.

z 68A

Western Perimeter Drive Western Vent Shaft Release Point WPD Kink (e) - 2/6 int WPD 10 metre position 2/5 intersection WPD 2/4 intersection WPD

Fig 3.28: Expanded plan view of WVS area.

69

Velocity Flow Profiles

Figure 3.29 gives a plan layout of the 2 Drill level

showing the positions selected for cross sectional

velocity profile measurements.

The technique employed to measure the profile was as

follows:

- Mark the site using paint on the walls, floor and roof

to define the correct grid, using proportional

spacing. Positions 1-4 in both horizontal and

vertical directions were marked.

Conduct an anemometer (Vane style) traverse to

determine the "traditional" velocity.

- Locate the anemometer at each of the grid positions and

determine the flow velocity at this point. Repeat to

the completion of all the grid positions at the

site.

Analysis of the results is given in Chapter 4.0.

69A

Z

Scale 1:100

Fig 3.29: Expanded plan view of WVS area with sites marked.

70

Positional Tracer Gas Release

Trials 65 to 87 were conducted to determine the

performance of the flow using positional release.

Subsequently this method was adopted as a standard in all

trials.

Figure 3.30 shows a view of the release site looking

upstream, with the node numbers indicated.

A consistent relationship appeared to exist between

release point and detection level. It should be noted

that a consistent release was provided by initiating

rupture at the base of the balloon.

The practice of thoroughly marking sites, and testing at

a range of node positions was continued throughout the

remainder of the underground experimental work.

3.5 TREATMENT OF DATA

The response curves from the chart recorder were

digitized to form a computer data file. This file was

modified using an IMSL (84) online routine, RECSPL, which

fits a spline relationship to a two dimensional array.

The resultant E. vs t curves were then plotted out. These

are given in Appendix 1.

7 0 A

KEY

* Tracer Release point ___ Tunnel boundary

Grid Line

X 1 2 3 4

Elevation - Looking Into Flow

Fig 3.30: Tracer release points across drive section.

71

Using the digitized form of the data, the mean time (t) 2

and the variance (o- ) were calculated for each curve

according to the discrete form of their equation, viz:

t = t > t.E.At. £ 1 1 1

S E.At. /! l l

(3.1)

I t2iEiAti

1 EiAti

2 •*- -2

a = — t (3.2)

— 2

Using the values of t and & , so calculated for each

curve the dispersion number (D/uL) was then calculated by

eqn (2.45)

Care was taken to ensure that the resultant values

conformed to the limits of the validity of the dispersion

model. For this purpose both the values of the calculated

D/uL and the shape of the actual curve were examined.

If the calculated D/uL is greater than unity, the

assumption of the dispersion model breaks down (69).

However, even with D/uL < 1, if the shape of the curve is

either multimodal or the curve has a very long tail then

the dispersion model of Sect 2.3.1 cannot be used.

Instead, a multi-parameter model was applied or, for long

tailed curves a graphical calculation was adopted which

72

is not critically sensitive to long tails. The graphical

calculation is based on the properties of normal curves,

where 68% of the total area under the curve is located

one standard deviation from the mean as shown in Fig

3.31.

It is obvious from Fig 3.31 that if the mean is taken as

occuring at the peak value of the curve then the 68% area

criterion would clearly not be too sensitive to the tail.

It should be noted, that the graphical calculation

outlined above would lead to some inaccuracies in the

D/uL values. Nevertheless, the results of graphical

calculation may be considered to be good approximations

of the main flow reality, since the presence of long

tails would not be the principal feature (dispersion

characteristic)of that flow. Extended tails in otherwise

reasonably normal response curves are caused by some of

the fluid being held back. This can occur by adsorption,

or by tracer being trapped within pores or, more likely

in mine roadways, by being held up in the many

semi-stagnant pockets (See Fig 3.13).

72A

•'e, max

JS, Inl

¥- = 0.000625 ut,

Fig 3.31: Relationship between D/uL and the dimensionless E curve (C~) for small extents of dispersion, after

Levenspiel (69).

73

CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 LABORATORY TESTS

The primary aim of these tests was to prove the

suitability of the tracer measuring apparatus (Sect

3.1.2) to detect and record small concentrations of

C2H2-air mixtures. As was shown earlier (Fig 3.6) the

detector-recorder possessed the reguired sensitivity and

linearity.

In addition to the above tests a series of runs were made

with the perspex pipe assembly (Fig 3.1) to obtain data

at different flow velocities for comparison with those

expected from theory (Sect 2.3.1). The experimental

results are given in Appendix 2, Table A.l and the

results of the calculations are shown here in Figs 4.1

and 4.2.

It should be noted that the small scale of the system

(Fig 3.1) restricted the velocity range that could be

used since the response time of the chart recorder was a 4

limiting factor. Hence K > 2 x 10 could not be used.

Also, since flow at K < 5 x 10 was not the main interest

in this study, tests were not conducted below this

Reynolds' number.

73A

1.0 1.5

Velocity (m/e) 2.0

Fig 4.1: Mean Time vs Velocity.

4x10^ 6 7 89 1x10* 2

R 3 4 5x10

Fig 4.2: D/ud vs Reynolds' Number,

74

In tracer studies, the first check of the system

performance is the conformity of the mean times between

measurement and theory (eqn (2.9)). The results in Fig

4.1 show that the observed relationship between t and u

closely agrees with theory, except for reasons noted

earlier, at the highest flow rate used (35 l/s).

2

Next using the o values, calculated from the response

curves, an example of which has been given in Fig 3.7, by

eqn (3.2), dispersion numbers (D/uL) were calculated (eqn

(2.45)), and then using eqn (2.50), values of D/ud were

extracted and plotted against 03 in Fig 4.2.

Comparing the results in Fig 4.2 with the published data

in Fig 2.8 it is obvious that agreement is very good. In

fact, good agreement of the data is not surprising since

the flow system used was for all purposes an ideal

system, viz a smooth pipe of constant diameter.

This ideality is further supported by the observed

relationship between variance and the flow velocity in

Fig 4.3. The slope of the line of best fit in Fig 4.3 is

very close to -3.0 which is the relationship predicted by

theory (eqn (2.53)).

74A

i nun .1 LO 10.0 100.

Velocity (m/s)

Fig 4.3: Plot of Variance vs Velocity Laboratory Results

75

4.2 LARGE TEST RIG RESULTS

As was the case in the work of Higgins and Shuttleworth

(2) , the aim of these tests was to examine the behaviour

of the technique in a large scale rig before taking the

technique underground. In fact, the duct assembly used

(Fig 3.8) parallelled the design employed by the above

authors.

The experimental results are given in Appendix 2, Tables

A2 and A3, respectively for cross-sectional and for point

injection. Figure 4.4 gives the measured mean times,

obtained from the tracer response curves by eqn (3.1), as

a function of the measured flow velocity. It is obvious

from Fig 4.4 that the results satisfactorily follow

theory. However, it is also clear from Fig 4.4 that the

mean times for point injection are, on average, slightly

higher than those for cross-sectional injection.

2

An examination of the measured o> values in Tables A2 and

A3 (Appendix 2) clearly indicates that these are higher

for point injection than for cross-sectional injection.

By way of illustration of differences involved Fig 4.5

2

shows a plot of c/ vs u for the case of L = 10m.

75A _ y

J m

o

1.0

0.9

0.8

0.7

0.4 _

P 0.6

3 0.5

A •o m

£ 0.3 1 0.2

0.1

0.0

£

® - Cron-Motlonal InJroUoa

X - Point toJsoUon

1 I ' I ' I ' I • I ' I ' I ' I ' I ' I 0 1 2 3 4 5 6 7 8 9 10

Velocity (m/s)

Fig 4.4: Mean Time vs Velocity for Large Tests Rig

LO 10.0 100.

Velocity Cn/s)

Fig 4.5: Log-Log plot of Variance vs Velocity, Large Test Rig Data

76

It is interesting to note that in addition to the

difference of the variances between the two injection

systems the relationship between cf and u is not quite

that expected from theory as was the case in the

laboratory tests (Sect 4.1) In this case (Fig 4.5) 2-2.5 2-3

o ck u rather than & & u. predicted by theory.

The larger variances in the case of point injection are

almost certainly caused by initial variance of the input

pulse. This is supported by the physical considerations

of the injection device which would inevitably impart a

lateral spread to the tracer on injection. In the case of

cross-sectional injection with the design of the injector

used and its position in the pipe (Fig 3.9), this initial

spreading of the tracer cannot occur.

Using eqn (2.48) the extent of this initial spread of the

tracer is estimated to have contributed a variation of

about 20. % to the total variance. From the view point of

the intensity of dispersion (D/ud) the two sets of data

(in Tables A2 and A3) are correlated for K > 10 by:

D/ud = 0.25 - 9.2xlO~aR (r*=0.87) (4.1)

for cross-sectional injection and

D/ud = 0.29 - 9.2xlO~aR (r2=0.81) (4.2)

for point injection.

77

In other words, the spread of the initial pulse with

point injection is equivalent to an increase of almost

10% in the measured intensity of dispersion of the flow.

It should be noted that this difference does not mean

that the main flow is more dispersed. The dispersion of

the flow remains the same - the difference is simply that

due to the difference of the injection method (Sect

2.3.3). After all, why should the way the tracer is

introduced change the flow pattern of the fluid if

everything else remains constant?

With regard to the observed proportionality of c with

u , rather than with u as predicted by theory, the

most likely explanation is the non-ideality of the piping

system used. This is supported by noting that in

non-circular tubes and channels it has been found (69)

that the dispersion coefficient (D) is affected by the

flow parameters to a slightly different extent than for

the ideal case given by eqn (2.41).

Additionally, a similar situation pertains also to head

losses in industrial flow systems. Thus, according to eqn 2

(2.2) Ap oi u , but this proportionality is seldom

observed in practice. It is more common to observe Ap a

1. <s-±. &

u . In the present case the head loss (Tables A2

and A3) have been found to be proportional to u as is

78

evident from the plot of the experimental results in Fig

4.6.

Finally, it is useful to give the range of the dispersion

coefficient values for the ducting system used. From eqn

(2.45) for L = 10m, D = 0.286 m2/s at the low velocity

(1.3m/s) and D = 1.604 m2/s at the high velocity

(6.8m/s). It is also pleasing to note that the dispersion

coefficients are in almost the same ratio as their

respective velocities and that this is in line with

theory (Sect 2.3.1). Additionally, the constancy of the

D/uL values for L = constant, evident in Tables A2 and

A3, is also in line with theory (Sect 2.3.1).

4.3 UNDERGROUND TESTS

Having established from the results of the large test rig

that the tracer injection and measurement technique was

satisfactory, preliminary underground tests were

commenced at the 4 Drill site. As the large test rig

results have shown that there was no difference between

cross-sectional and point injection techniques if the

initial variance of the latter was accounted for, the

point injection technique was adopted underground.

An additional advantage of this technique was that it

also made a one man operation possible.

78A

o

100.0 _

o h-

s = ,3 < 1.0

.1

—

M^WB

'm^m}

—

~ r

M

zz I

~i nun

o , ©/

(0/

Ik/TO

i n u n

K<ry

6> Test I

A - Test 2^

IIIIIII Mini! .1 1.0 10.0 100.0

U (m/s) - Velocity

Fig 4.6: Head Loss vs Velocity (log-log), Large Test Rig

79

Initial results at the 4 Drill level could best be

described as a failure of the support equipment as

detailed in Sect 3.3.1. The first successful results in

obtaining tracer response curves were at the 2/8 cross

cut on the 2 Drill level.

4.3.1 2/8 Cross-cut Tests

The results of tests 1=»64 conducted in the 2/8 cross cut

(Fig 3.12)are detailed in Appendix 1. By inspection of

the results in Appendix 1 the most obvious common feature

of the response curves obtained is their irregular

appearance. This contrasts quite sharply with the

response curves obtained in the laboratory and large

tests rig (Figs 3.7 and 3.10), but parallels the

underground results of other workers (Sect 2.4 and Figs

2.14, 2.17 and 2.18).

It should also be noted that the NCB (2) and the USBM

(3-6) results were obtained by analysing tracer

concentration in air samples, taken at discrete time

intervals following release.

In the present work tracer concentration was recorded

continuously, thus, all changes, both small and large,

were recorded, making the irregularities of the response

80

curves even more exaggerated than would be the case with

discrete sampling.

Following the laboratory and the large test rig data

analysis procedure, results were first checked to ensure

consistency of the mean times. Figure 4.7 gives the plot

of the experimental mean times vs distance between

release and measuring points for three different air flow

rates (as determined from an anemometer traverse or smoke

tube release and detection). The flow rates were varied

by adjusting the regulator at the Western end of the 2/8

drive (Sect 3.3.2).

It is evident from the results in Fig 4.7 that the mean

times are reasonably linear with distance for each test

series. The slope of the t vs L line is the average flow

velocity and these velocities are compared in Table 4.1

with those obtained by the traditional techniques

referred to above.

Table 4.1 - Results of Air Velocities (m/s) Measured by

Two Measurement Techniques

Traditional

0.25 0.45 0.84

Tracer

0.375 0.551 0.825

80A

60 -a P

50 -=

40 T . n

I 30 ~

20 ~

10 -=

0 l'i 1 | I I I I I I I I T | I I I I I J I I I | I I I I I J I I I | 1 1 I I I

10 20 30 40

Distance (m)

Fig 4.7: Plot of Mean Time vs Distance; Large Test Rig

81

The results in Table 4.1 show that the two techniques are

in reasonable agreement at the higher velocities but not

at the low velocities. The error at the lower velocities

is almost certainly in the traditional method since it is

well known in practice that traditional measurements of

low velocities are notoriously (60) unreliable.

With regard to the measurement of low air velocities it

is of interest to note that Higgins and Shuttleworth (2)

concluded from their tracer work that "The tracer

technique is especially valuable in the measurement of

small quantities of air where the velocities are too low

to be measured by vane anemometers".

Next a comparison of variances (Table A4) is shown

graphically in Fig 4.8. By inspection of Fig 4.8 it is

evident that although widely scattered, the results do

show a definite trend, both with respect to distance and

with respect to the flow velocity, but only when the

latter results for L > 15m are considered.

Before the results are analysed it is necessary to

establish which of the flow models in Sect 2.3 may be

involved. Inspection of the actual response curves shows

that apart from a few, obviously irregular shaped curves

and the true bi-modal response of Test 22, the responses

81A

Q- T « + Ser.es

O- Test SeKes

0

r W l i i u | u i 11 m i| 11 n 11111 | rr

10 20 30

Distance (m)

rr\ r i 111 40

Fig 4.8: Variance vs Distance; Large Test Rig

82

are of the kind that might be expected from a dispersion

model.

The dispersion model predicts (eqn (2.53)) that c/2 cx L , _ 2 3

and also c, a i/u . Figure 4.8 shows that for a constant

flow velocity the variance increases linearly with

distance. So, in this respect the results agree with

theory. However, this increase is not what it should be

for the results at the high velocity (u = 0.825 m/s).

Since reproducibility of the results could be considered

satisfactory (Table A4) it can be concluded that the

reason for the anomalous behaviour is connected in some

way with the actual flow pattern rather than with a

system malfunction. The effect of the flow velocity on

variance changes is also anomalous, not only for the

short distances (L < 15m), which is obvious from Fig 4.8,

but also for the larger distances, where variance is

inversely proportional only to u, and not to u as

predicted by theory. This difference may have been caused

by the non-ideality of the roadway.

Although the latter explanation was reasonable, and also

supported by literature findings, for the difference in

the velocity effect observed in the large test rig

results (Sect 4.2), the difference involved here is very

83

much greater for the same reasoning to be sustainable.

Unfortunately no data are available in the literature

that may confirm or negate such a possibility, and

research into this aspect of dispersion mechanics is

clearly indicated.

Table A4 includes the calculated values of the dispersion

number and the intensity of dispersion calculated by eqn

(2.50) using the equivalent diameter of the actual

roadway in the d/L term. Because the latter results are

an order of magnitude different from those expected (Fig

2.8) a reverse calculation was performed.

In this case the value of 0.22 corresponding to 03=10 was

used for D/ud (Fig 2.8). Then with the known L and D/uL,

independently calculated from the measured variances, the

values of d were obtained. By inspection of the results

in Table A4 the range of d values lies between 0.01 and

1.2m, with a tendency for an increase in d with the flow

velocity.

Since the diameter so calculated is much smaller than the

actual diameter of the roadway (d=4.95m) then these

diameters may be interpreted as those characterising some

"flow tubes" in the main airways. To investigate this

phenomenon the test site was transferred to the West Vent

84

Shaft area. The objective there was to measure much

larger cross-sectional area of the flow as the air

converges at the regulator.

4.3.2 West Vent Shaft: Preliminary Tests

The response curves of tests 46=*64 (Appendix 1) describe

the early results of the tests. Tests 46=^54 that were

detected with the box evase gave noisy responses

(Appendix 4) for which the cause was established as being

the "flapping" of the box in the high velocity airstream

at the detection position. The box was removed and tests

55 to 64 were then carried out with the detector head

alone, as was done previously in the large test rig with

good results. However, since only test 58 was detected,

it was felt that a large number of resultant "lost

pulses" made the use of an evase necessary. Subsequent

tests therefore employed the evase described in Fig 3.27.

The question that has to be addressed next is: should the

results obtained under the above conditions be analysed

at all or should they be scrapped altogether?

The answer to this question should rely on establishing

validity of the measurement, ie. deciding that what is

being measured does in fact represent the characteristics

of the flow that actually exist in the roadways.

85

Elementary considerations show that if the testing

equipment is reliable - and this was proved so earlier

(Sects 4.1 and 4.2) - then the response curve is

diagnostic of the features of the flow. As the general

shape of the curves (Appendix 1) is indicative of

dispersed flow with superimposed patterns of Fig 2.9 then

the dispersion model may be used with the only limiting

conditions being those of the model itself (Sect 2.3.1).

The fact that at the injection point the cross-sectional

area is much larger than at the measurement point, and

the air velocities are an order of magnitude different,

does not in any way invalidate the dispersion model and

its mathematics. The proof of this assertion follows

directly from eqn (2.43) and its result in eqn (2.45) and

also eqn (2.53). A non-mathematical explanation is to

consider the behaviour of an ideal plug flow vessel such

as depicted in Fig 4.9. Since ideal plug flow is always

ideal then a pulse injected at the entrance will appear

unchanged in no way at the exit, no matter if the flow

speeds up, slows down, converges or diverges during its

passage.

Table 4.2 summarises the particulars of tests 44=»64, and

Fig 4.10 shows the location plan in more detail with

positions of the test release points and detector marked.

85A

Response

Input Pulse

Fig. 4.9: Tracer Response in an Ideal Plug Flow Vessel

2/4 x WPD

2/5 xT .WPD

1

Kink >> MWP

\ A Detector

Fig. 4.10: Expanded view of WVS Release points

86

Table 4.2 Particulars of Tests 46= 64

Location

WPD Kink

2/5XWPD

2/4XWPD

2/5XEPD

Mid WPD

L (m)

10

22

51

350

6

Test No.

46,47*,52,59,60

48^49^55,56/57

50^54,62,63

51,53.64 * *

58,61

Comments

Long Tail

Bi-Modal

Tri-Modal

Lost Pulses

Normal

Velocity

2.1

0.8

0.4

0.7

1.3

NOTE: nn, indicates a detected pulse rm indicates a pulse released toward the detector

without the box evase Velocities indicated are at point of release

The analysis of the result of tests in Table 4.2,

follows.

At the WPD Kink the response shows . a long tail,

indicating that some air is slow moving. From the

physical situation in Fig 4.10, some flow from the WPD

Kink to the regulator via the Northern wall may be

expected, and this was picked up by the detector in the

form of the long tail. Ignoring the tail, the

characteristics of the main flow are calculated (Sect

3.5 and eqn 2.45) as:

t = 12.6 s o"2 = 29.1 s2

u = 0.8 m/s D/uL = 0.096 D/ud =0.2

87

The above results are most reasonable and consistent with

the physical reality in Fig 4.10. The calculated

dispersion coefficient is 0.77 m2/s which is slightly

more than double the value of 0.286 m2/s in the large

test rig for similar conditions. This is also reasonable

since increased dispersion activity can almost certainly

be expected in the underground environment of the test

site.

2/5 x WPD - The two response curves are considered to be

a satisfactory duplication of results for what must be

considered a potentially unstable flow region. The

bi-modal nature of the response suggests branching flow

in an approximately 60:40 split. Using the procedure in

Sects 2.3.2 and 3.5 the following results are obtained:

TEST 48: t = 43 s — — — ^

tL = 61 s 2

TEST 49: t = 48 s ^ — — — — • ^

tL = 68 s 2

Since variances were obtained by approximate graphical

separation techniques they are only reasonable estimates

and therefore not suitable for further calculations. This

explains the absence of dispersion parameters in the

above list.

2 2

c = 26 S I

2 2

& „ = 35 S 2

2 2

«y = 55 s i

2 2

88

However, the available results show that in both cases

— — 2 2

t±/t2=1.4 and o'i/©2=1.4. This again confirms satisfactory

duplication of results.

The calculated mean flow velocity in the main path

(L=22m) is 0.48 m/s and the length of the second path is

31m (ie 1.4 x 22 = 31m) assuming that the increased time

(t ) is due to the longer distance and not to any

velocity reduction. In all likelyhood, both effects are

involved and this would be more consistent with the

physical situation shown in Fig 4.10.

2/4 x WPD: The response curve suggests that the flow

takes three different paths which is a distinct

possibility from the geometry of the area (Fig 4.10) and

the very low anemometer velocity measured at the release

point (Table 4.2). The calculated parameters are:

Volume of flow regions 30:50:20 (approx.)

tL = 118 s vz = 28 s2

i I

t = 136 s cf\ = 42 s2

2 2

t = 160 s vZ = 65 s2

The explanation here parallels that given earlier for the

2/5 cross cut response. However, the third peak suggests

that the third path was that of a slow flow along the

89

wall possibly the Northern side wall. An estimate (from

mean times) of the distances involved is

L± = 51 m L2 = 59 m Lg = 69 m

The above results appear reasonable and the flow paths

suggested by the results are not impossible for the

physical area (and network) being considered.

Mid WPD The two duplicate response curves are for all

practical purposes identical. The differences between the

two responses are minimal and are caused by the normal

variations in the flow due to nearby mining activity as

demonstrated by Higgins and Shuttleworth's results (2) in

Fig 2.13. The calculated parameters of the two response

curves are:

ii = 1.18 m/s

D = 0.216 m /s

u = 1.17 m/s

D/uL = 0.024 d = 0.7 m D = 0.158 m2/s

The calculated velocity is in reasonable agreement with

that measured by the anemometer (cf 1.3 m/s Table 4.2).

Because the release distance was short, the calculated

intensity of dispersion was low (=0.03) but the "flow

TEST 58:

TEST 59:

t = 5.08 S

D/uL = 0.029

t = 5.12 s

2 2

& = 1.5 s

d = 0.9 m

2 2 <y = i.l s

90

tube" diameter of =*0.8m is in line with the 2/8 cross cut

results (Sect 4.3.1).

Likewise, the values of the dispersion coefficient are in

line with those obtained in the large test rig (Sect 4.2)

and are about one-third of those calculated from the

results of WPD Kink response curves given in this

section. The reasons given there for the difference in

the values of the dispersion coefficients apply here

without modification.

2/5 x EPD this test gave a "lost pulse" result, which

can be readily explained by the fact that the distance

involved was 350m and the dilution of the tracer was such

that the final concentration was below the sensitivity

level of the detector. However, there were other releases

much closer-bye (Table 4.2) which also gave "lost pulse"

results. The only possible explanation for these is that

the signal travelled outside the detector head or its box

evase.

This was actually proved by chance when one of the

balloons, prepared for a test at one of the release

positions, burst at the same time as the operator was

adjusting the span of the recorder. In the event, the

arrival of the C2H2 was detected by smell but not

91

recorded by the detector. However, when a burst of

C2H2 was released in front of the detector head the pulse

was recorded immediately. This chance occurence,

indicated a "layering" phenomenon and as this was

something unexpected a different plan of tests was

initiated and results are described in the next section.

4.3.3 West Vent Shaft - Positional Release

These tests were conducted at five different sites as

shown in Fig 4.10 with systematic tracer releases at

points over the site cross section as detailed by the

coordinate view in Fig 3.30. The measurement equipment

and procedure used were as given in Sect 3.3.3 using the

final design evase (Fig 3.24).

Unfortunately, standard balloon releases at Site 5 could

not be detected because the final concentration of the

tracer was again below the sensitivity level of the

detector. In other words, the same problem was

experienced here as that encountered with the test at the

2/5 cross cut-Eastern Perimeter Drive intersection

release described in Sect 4.3.2. Although the detection

of positional releases failed, a cross-sectional release,

to be described later, was successful.

92

The response curves obtained in the Site 1 - 4 tests are

given in Appendix 1 and Tables A5-A8 in Appendix 2 give

the results obtained.

An examination of the response curves 65=^191 (Appendix 1)

indicates that overall the curves are indicative of

dispersed flow. There are some anomalies to this and a

number of "noisy" responses. Considering that the tests

were made over a period of time with different levels of

mining activity occuring, differences in the results are

not only inevitable but what may be more important is

that they have to be considered normal behaviour.

Table A5 (Appendix 2) gives the Site 1 results which

include the calculated dispersion parameters and

velocities in addition to the measured t and &z. The

initial detector head position (Tests 65-»78) was central

(see Fig 3.24) and this resulted in a number of lost

pulses from certain release positions. As this result,

also observed earlier (Table 4.2), indicated "layering"

flow further releases were made with the detector head

located at various positions other than central in the

regulator, eg left, right and centre-up.

As shown in Table A5, a release from every grid

coordinate was detected if the head was in the

93

appropriate position. This result, therefore, provides

strong evidence that the air flow (at Site 1) is layered

or segregated. Inspection of the last column (d ) in calc

Table A5 gives an approximate indication of diameters

characterising the dimensions of the "flow tubes". By

inspection of the calculated values there are some

anomalies, viz some values exceed the measured diameter

of the roadway at Site 1 of 4.87m.

The reason is most probably associated with an

instability of air flow at some test times caused by

events of short duration such as fan surges, ore dumps,

stope rills, upcast shaft water curtain

formation/release,truck haulage and so forth. Because

such events may be expected to have a much greater effect

on the variance compared with mean time (eqns (2.53) and

(2.23)) then large variations in d 1 are inevitable. caic

This is because the magnitude of variance strongly

influences D/uL from which d is calculated by eqn (2.50)

with constant D/ud taken as before, equal to 0.22 for

K > 105.

— 2

The above explanation is supported by comparing t and o

for a duplicated result, eg:

94

Position 3,1

Curve 67 91 94

Position 3,2

Curve 92 95

Position 3,4

Curve 111 112

Position 4,2

Curve 79 80

Date

9.8.86 21.8.86 21.8.86

Date

21.8.86 21.8.86

Date

21.8.86 21.8.86

Date

15.8.86 15.8.86

t

13.5 9.5 9.2

t

8.2 10.8

t

18.6 19.1

t

7.16 8.4

2

a 21.83 1.41 0.04

2

0.17 8.40

2

a

26.29 112.36

2

8.47 0.06

d

6.26 0.82 0.03

d

0.13 3.76

d

3.97 16.10

d

8.78 0.04

It is clear from the above results for position 3,1 that

mean times can also be different on different days when

as far as it could be ascertained there were no

significant changes in the mine operation.

Additional evidence for the existence of transient

changes and flow instabilities, referred to above, is

provided by the observed results in all tests that a

consistently detected release position may once in a

consecutive number of releases report as a "lost pulse".

It should be noted that a single test number in all

underground tracer tests sometimes represents 5 or 6

consecutive individual releases because of "off chart"

95

recording (see Section 3.3.3). So when the chart span was

correctly adjusted for an "on-chart" recording to then

have a "lost pulse" was more than an annoying experience.

Because of the above transient effects and the normal

differences in the flow of the ventilating air, referred

to earlier and also noted by other investigators (2-6) in

their tracer work, the guestion of the reproducibility of

the results should always be borne in mind. In tracer

work the most sensitive reproducibility test is the

reproducibility of the mean times. If these are not

reasonably reproducible then the validity of the tests

must be regarded at best as questionable and at worst as

useless.

On this basis, the reproducibility of the present results

have a maximum relative error of 31,7% (Position 3,2 Site

1) and a minimum relative error of 3.2%. Since most

duplications have been well below the maximum error of

31.7%, it is therefore considered that the reproducibility

of the results is reasonable.

2

As far as the differences in ct r and hence d, are

concerned, it is considered that they still provide

reasonable relativity. In other words, a "flow tube" with

a low d , value may be expected to be smaller in extent

than a "flow tube" with a large d -. value.

96

A final estimate of difference from Site 1 t and ctz data

in Table A5 that can be made is to pool all the t and ct

values to obtain a grand mean time and a mean variance to

calculate the diameter of the roadway.

The calculating procedure is equivalent to considering

that a single cross sectional release gave the mean time

and variance used in calculations. The result is:

t = 13.1s and ct = 10.3 s

Then, combining eqns (2.50) and (2.58) and solving for d

with D/ud=0.22 for R > 10°

d = "2" L _ 2 (4.1) 2x0.22*(t)

The term not precisely known in eqn (4.1) is L, the

distance from Site 1 to the regulator. As is evident from

Fig 3.29, many possible tracer paths may be involved.

Taking the mean distance of 29.8m then on substitution in

eqn (4.1) the result is:

, 10.3x29.8 . __ d = — = 4.07m

2x0.22x(13.1)

Since the measured diameter of the roadway at Site 1 is

4.87 m the calculated value of 4.07m is in reasonable

agreement - the difference being less than 20%. This

97

result therefore may be viewed as supporting the

applicability of dispersion mechanics theory in

underground mine ventilation.

Release tests at Sites 2, 3 and 4 concentrated on

delineating the flow layering detected at Site 1 with

the particular aim of finding out where it may originate.

Consequently, only the central detection position in the

regulator was used. The results of the tests are given in

Tables A6-A8 (Appendix 2). By inspection of the results

obtained at these sites it is evident that the flow is

layered at these sites also. Unfortunately, and for

reasons noted earlier in this section, tracer tests using

the standard balloon procedure could not be extended to

distances beyond that of Site 4.

Therefore it is not possible to answer, at least by the

positional tracer release technique, how far upstream did

the observed flow layering extend. However, it will be

shown later that an indirect answer to this question may

exist.

It is of interest to note that the results in Tables

A6=>A8 also show the expected range of dispersion

parameters when the distances involved are accounted for.

Hence, analysis of these are omitted, but they of course

98

can be readily obtained if needed by simply repeating the

analytical procedure given in the previous few pages for

the Site 1 results.

Next, the response curve given in Fig 4.11, of the cross

sectional release test at Site 5 (Test 192) is analysed.

This test was carried out by inflating a meteorological

balloon (obtained from the Meteorological station) with 3

approximately 1.2 m of C2H2 and then bursting the

balloon at the site and recording the response at the

West Vent Shaft regulator in the usual manner, with the

detector head in the central position.

Figure 4.11 shows that the response curve of this test is

clearly bi-modal and that the slow rise at the beginning

and a slow fall at the end are a clear indication of a

dispersed flow. The bi-modal nature of the response curve

on the other hand is indicative of a parallel flow (Sect

2.3.2) .

Although as is usual in practice the response curve in

Fig 4.11 does not show the idealized separation of the

two flow paths of Fig 2.10, calculations of the flow

parameters using eqn (2.56), and that of the two D/uL

values involved, using Fig 3.31 procedure, can still be

performed with graphical separation. This, it will be

98A

0.2

O 8) 0.1 -J

Ui

0.0 rTjfrrm i n [rm i riTT[TmTTni{nTTTnrrpTrnrrnT|rrriT 50 100 150 200 250 300 350 400

TIME (sec)

Fig 4.11: Response curve for Test 192

Vi= 0.45 (D/uL) =- 0.021

Fig 4.12: Flow model for the response of Fig 4.11

99

recalled, was the procedure used in analysing the

underground tracer results of other workers (Sect 2.4).

The results of the analysis of the response curve in Fig

4.11 are:

t„ = 240s ctz = 1470s2 1 1

t, = 325s cfZ = 1690s2

2 2

The corresponding flow model and its relevant parameters

are given in Fig 4.12.

It is noted that the "size" of the two flow branches are

given in Fig 4.12 in terms of their volumes. This is a

necessary result of eqn (2.56). It is also noted that the

flow model in Fig 4.12 corresponds to the underground

physical situation of the relevant area in Fig 3.12, with

Site 5 being at the exit of the 2/7 North cross cut.

Therefore, whilst it is possible to accurately measure

the distances involved as has been done in Fig 3.29, it

is clear that they cannot be calculated accurately in

this case by the relationship L = V/A since the cross

sectional area of the two flow paths, viz paths 5-*2-»l->0

and 5-»4=»3->l=>0 (Figs 3.12 and 3.29), are not constant.

100

Nevertheless, with the reasonable assumption that in the

Western end of the 2/7 roadways the cross sectional area

of the Path 1 circuit is twice the volume of the Path 2

circuit, and both paths thereafter have a "constant"

cross sectional area of 25 m , then 1,± = 135m and

L2 = 180m. By inspection of Fig 3.29 the above calculated

distances are not too different from those actually

measured viz. 146m and 175m, respectively.

It is also of interest to note that the calculated D/uL

parameters for the flow model in Fig 4.12 are not as

different as may have been expected.This indicates that

the operative dispersion intensities are somewhat

different in each branch and possibly caused by the

different flow path geometries evident in Fig 3.29.

Although cross sectional release test like the one

described above, would have been of interest the cost of

conducting such tests was prohibitive. Additionally,

cross sectional release, although theoretically capable

of detecting "layered flow" if it closely corresponds to

the pure convection model of Sect 2.2.3, would be most

unlikely to be as successful (and as practical) in the

underground conditions as the point release method used

in this study.

101

4.4 POSITIONAL ANEMOMETER TRAVERSE

Anemometric positional velocity data were obtained at the

same sites as the tracer release was carried out; using

the vane anemometer and the measuring technique as

described in Section 3.4.4. Measurements were made at the

nodes according to Fig 3.30, ie at the same points used

for the tracer release. Additional to Sites 1-4, four

other sites, including Site 5, were also investigated,

with Sites 6,7 and 8 being in the vicinity of the 2 Drill

entrance some 600m distant from the West Vent Shaft

regulator.

The location of Sites 6,7 and 8 are indicated in Fig 3.12

The results of the anemometer survey in terms of

positional velocity are given in Appendix 3. It should be

noted that the measured raw velocity values have been

adjusted. This adjustment was based on two sources; the

standard calibration corrections for the anemometers

(determined by Scientific Instruments P/L) and secondly

by comparison with the centre line reading. Due to the

length of time spent at each site, a "drift" in

velocities, inherent to the mine ventilation, was

expected. To account for this drift a centre line

velocity was taken parallel to velocities measured at the

individual positions. The expected drift was found to not

102

be significant (=*2%), and a correction to the average

centre line velocity was applied on a linear basis for

each positional velocity.

Using the data in Appendix 3 traditional velocity

contours exemplified by the Site 1 results in Fig 4.13,

were prepared. However, this simple form of data

representation and its computer aided equivalent in Fig

4.14 was not found useful for analysis and was abandoned.

Instead, suitable data representation and analysis was

achieved by using commercially available software that

allowed the plotting of a topographical surface for the

positional velocities. The program, PLOTCALL distributed

by Golden Software P/L (1984) uses a Kriging method (85)

to determine the data values at each point of a 50 by 50

grid for the test site velocities.

4.5 COMPUTER ANALYSIS OF POSITIONAL RESULTS

Analysis of both tracer release and anemometer results

were carried out using the PLOTCALL package. After

several trials at different extents of smoothing, a 0.99

value was selected (where 1.0 gives no smoothing and 0

complete averaging of input data) as the standard for all

generated results. The reason for this choice is both

mathematical and physical as may be seen by comparing the

102A

CALCULATION iHin

Fig 4.13: Hand Drawn Velocity Contours - Site 1

1 i " * — ' • * • - ' ' - • • - * •

UL.I I wT*i

Site 1 - Contours, 0.99 SMooth, 0-04 ty 0.(

Fig 4.14: Computer Generated contour Plot - Site 1

103

results of the smoothing levels at 0.9 and 1.0 values

(Appendix 4) and the companion results at 0.99 level in

Fig 4.15.

Mathematical reasons are associated with the number of

degrees of freedom available and the fact that all points

at the flow boundary region, ie. the walls of the

roadway, must be set at zero as required by the boundary

layer theory (86). Physical reasons are actually a

compromise amongst the accepted physical reality of the

continuum (0.90 level), and the improbability (1.0) level

and the conceptually acceptable physical representation

of the segregated flow (0.99 level).

An important point to note, however, is that in each case

exactly the same data computation is performed so

similarities and differences can be compared exactly even

though they may not exactly correspond to the actual

macroscopic (and microscopic) distribution of the flowing

volume elements bounded by an impervious surface (ie. the

tunnel walls).

4.5.1 Tracer Results

The results in Tables A5=>A8 of the analysis of tracer

release data are shown in Figs 4.15=#4.19. Fig 4.15 shows

1037A

Fig 4.15: Site 1 Positional velocities by tracer all head positions

Fig 4.16: Site 1 Positional Velocities by Tracer, central head position only.

103AA

Fig 4.17: Site 2 Positional velocities by tracer.

Fig 4.18: Site 3 Positional velocities by tracer.

103AAA

Fig 4.19: Site 4 Positional velocities by tracer.

104

all the Site 1 data, whilst Fig 4.16 gives the data of

the central detector head position only. The latter is

therefore comparable to the results of sites 2-4 (Figs

4.17=^4.19) which featured a central detector location

only.

Inspection of Figs 4.15=»4.19 shows that all results are

similar in appearance which is not unlike a bundle of

tubes, the tips of which extend forward to a lesser or

greater extent.

Figure 4.15, viz the complete results in Table A5

(Appendix 2), clearly shows low velocity "flow tubes" in

the x = 1 position and high velocity "flow tubes" at the

x = 4 position, except for the x,y = 4,1 "tube" which is

low.

The positional features of the all-positions results in

Fig 4.15 are parallelled in Fig 4.16 which displays only

the central detector head location results. This,

therefore, indicates that the properties of the

positional "tubes" are constant. In other words, a "flow

tube" at any given x,y position in the coordinate grid of

Fig 3.30 has exactly the same characteristics at all

times.

105

Moreover, the "tube" also exists at all times and does

not disappear just because the detection system fails to

detect it. The results in Fig 4.15 of the high velocity

"tubes" at the 4,2=»4,4 and 3,2=>3,4 x,y positions are in

line with the physical situation (Fig 3.28) of the area

involved, in that it is a shorter, lower resistance path

to the West Vent Shaft Regulator on this side of the

drive. The low velocity "tubes" in Fig 4.15 at the other

positions, except 4,1 are likewise in accordance with the

physical situation at the other wall of the Western

Perimeter Drive to West Vent Shaft path. The low velocity

"4,1 tube" is however, puzzling.

The only reasonable explanation is that the flow there is

a low flow along the floor before ascending at the

regulator. This explanation is supported by the generally

lower velocities at the y = 1 level. Since the 1,4 "tube"

is also a low velocity tube then the same explanation

must apply there also. This is not unreasonable from the

physical point of view of the flow path involved (Fig

3.29) .

Comparison of Figs 4.18 and 4.19 shows quite clearly that

for all practical purposes they are identical.

Considering the fact that the two sites involved (Sites 3

and 4, Fig 3.29) are in the same section of the exhaust

106

flow from the 2/7 cross cuts, the result is not

surprising. However, the result does give added support

that dispersion mechanics also works underground.

With respect to the Site 2 results of Fig 4.17 inspection

shows that they are very nearly reproduced in the Site 1

results (Fig 4.16). In fact the Site 1 results are an

almost exact combination of the Sites 2 and 3 results ie.

Fig 4.15 = Fig 4.17 + Fig 4.18.

The reason for this may not be immediately obvious.

However, it becomes so when it is remembered that, unlike

traditional velocity surveys at a given cross section of

a roadway, tracer test velocities are the velocities for

the whole path length involved. This is made more clear

by referring to eqn (2.9) from which:

L u = —

t

Finally, from the results presented here, it can be

firmly concluded that the "layering" character of the

flow extends upstream of the West Vent Shaft to Site 4 in

the Western End of the 2/7 South cross cut and to Site 2

in the 2/6 South cross cut.

107

4.5.2 Anemometer Results

The results of the analysis of the anemometer data

(Appendix 3) for Sites 1=*8 are shown in Figs 4.20«*>4.27

inclusive. It should be noted that these tests were

performed at the same West Vent Shaft regulator opening

as all of the tracer release tests were carried out.

Therefore, flow conditions may be expected to have been

essentially the same in both cases.

Inspection of Figs 4.20=»4.27 shows that again the "tube

bundle" character is a common feature of the flow - from

Site 8 at the 2 Drill entrance (Fig 4.27) to the West

Vent Shaft exit, or more correctly to Site 1. With some

notable exceptions the "tube bundle" is more or less

symmetrical about the centre axis, ie. the highest

velocity is in the centre. Notable exceptions are Figs

4.20, 4.26-M.27.

By reference to Figs 3.12 and 3.29 the above exceptions,

apart from that in Fig 4.26, can be readily understood

since they correspond to the sites (Site 1, 6 and 8) at

which the flow is about to, or has already turned around

a corner. In the case of Site 6 (Fig 4.25) the flow is

not only segregated but the velocities are relatively low

compared to those at most other sites. These low

Fig 4.20: Site 1 Positional velocities by anemometer.

Fig 4.21: Site 2 Positional velocities by anemometer,

107AA

Fig 4.22: Site 3 Positional velocities by anemometer.

••'-TuVVV-'

Fig 4.23: Site 4 Positional velocities by anemometer.

107AAA

Fig 4.24: Site 5 Positional velocities by anemometer.

Fig 4.25: Site 6 Positional velocities by anemometer,

107AAAA

Fig 4.26: Site 7 Positional velocities by anemometer.

"•Car

Fig 4.27: Site 8 Positional velocities by anemometer,

108

velocities at Site 6 are expected since as Fig 3.12

shows, a part of the intake air after passing Site 8

enters the 2/8 North cross cut (Site 6) while the

majority continues along the Eastern Perimeter Drive to

the 2/7 cross-cuts. The flow is later recombined, mostly

at the Western Perimeter Drive and through the slot

connecting the 2/8 and 2/7 drives, and essentially

completely at the West Vent Shaft.

The profile of an increasing velocity from points 1 to 4

along the x coordinate in Fig 4.26 is an interesting

results considering the test location viz. Site 7.

Intuitively, in view of the result at Site 6 (Fig 4.25),

one would expect a reverse result at Site 7 to that in

Fig 4.26, or a symmetrical pattern. The explanation which

is suggested by the above results is that the different

kinetic energies of the "flow tubes", clearly already

present at Site 8 (Fig 4.27), have a long lasting

influence on the flow distribution downstream. Thus, the

highest velocity at x = 4 in Fig 4.27 and consequently 1 2

very much higher kinetic energy (=~Pu ) volume elements

are easily carried across the entrance into the 2/8 North

to Site 7 and probably well beyond it. In fact some trace

of the Site 7 pattern (Fig 4.26) appears to still exist

at Site 5 (Fig 4.24) but not beyond (cf Figs 4.21 and

4.23).

109

The interpretation of the essentially symmetrical flow in

Figs 4.16=^4.19 and Fig 4.21 can also be readily made by

reference to the location of the respective sites, but is

omitted here for the sake of brevity.

Finally, it should be noted again that the results in

Figs 4.15-4.27 were all obtained at the same regulator

setting. However, additional anemometer surveys were also

carried out at a different regulator setting which gave

an average velocity of about two thirds of the original

value, viz 0.96 m/s as against 1.53 m/s. The

corresponding Reynolds' Numbers are 3.1*10 and 5.0x10 .

Figures 4.28-M.31 show the Sites l-»4 results for the low

flow velocity. If these results are compared with the

high velocity results obtained at the same sites (Figs

4.20 •* 4.23) it is obvious that the two patterns are for

all practical purposes identical. This therefore means

that the velocity of the general body of air - at least

within the above range and most probably well outside it

too - does not have a significant effect in changing the

"tube bundle" character of the flow.

109A

Fig 4.28: Site 1 Positional velocities by anemometer (low velocity)

Fig 4.29: Site 2 Positional velocities by anemometer (low velocity)

109AA

Fig 4.30: Site 3 Positional velocities by anemometer (low velocity)

Fig 4.31: Site 4 Positional velocities by anemometer (low velocity)

110

4.6 COMPARISON OF TRADITIONAL AND TRACER RESULTS

It is evident from Figs 4.15=^4.31 of the previous

sections that both sets of results show the same "tube

bundle" feature of the flow. Hence, in this respect

traditional and tracer results compare very well. The two

sets of results are also complementary in that one set of

results alone may still leave doubt, particularly the

traditional ones, as to the reality of the results. This

is because, for example, the traditional results in Figs

4.20=>4.31 do not by themselves prove the reality of a

"tube bundle" or layered flow. Moreover, the very nature

of the anemometer survey method is incapable of any

confirmation of this sort.

The tracer tests on the other hand, can resolve this

impasse, and also provide other information that simply

is not obtainable by traditional methods. Thus, the

positional tracer release results in Sect 4.5.1 leave no

doubt about the layering of the flow since this feature

of the flow is confirmed physically, ie. depending on its

release point at a site the tracer either flows into the

evase and is detected or it bypasses the evase and is not

detected.

Ill

In other words, the tracer tests and specifically the

point injection technique, give a straightforward Yes/No

answer.

Although as shown in Sect 4.1.5, tracer tests also give

the flow velocity results in the same way as the

traditional methods do, the latter are still necessary

if for no other reason than to confirm the finding of the

tracer tests. However, there are some instances where

this cannot be done. For example, the result of the

meteorological balloon test at Site 5 (Fig 4.12) cannot

be confirmed by traditional methods. Other examples of

this kind were included in Sect 2.4.

One important difference between the two methods concerns

air balance and velocity questions. For example the air

flow at Site 1 must equal the sum of the airflows at

Sites 2 and 3 (Fig 2.39), ie.

UA = U2A2 + uaA3 <4-2>

From anemometer results in Appendix 3 and making the

usual assumption of equal cross sectional areas

throughout, the air balance is:

1.53 = 0.69 + 0.76

^ 1.45 (High u)

112

0.96 = 0.43 + 0.48

=* 0.91 (Low u)

By inspection the balance at both velocities is

satisfactory.

However, if the tracer determined velocities were to be

used in eqn (4.2) the result would be:

1.83 = 1.69 + 1.67

* 3.36

Comparison of the above results forcefully confirms the

difference between traditional and tracer results

referred to in Sect 4.5.1, viz., that traditional

velocity is an average velocity at a roadway

cross-section whereas the tracer velocity is the average

velocity in the roadway for the length considered (ie.

from release point to detector).

It is this property of the tracer velocity which is the

more significant since it includes implicit statements of

the history of the flowing volume element from its source

to its sink.

Nevertheless, if it is desired to use the tracer

velocities for air balance purposes, then path geometry

has to be accounted for in the calculations also.

113

It should also be pointed out that considering the

physical estimation of the area (Fig 3.12) it would be

expected that for Site 1 both the anemometer and the

tracer determined velocities should agree closely, but

not exactly. By inspection the two results viz. 1.53 m/s

(anemometer) and 1.83 m/s (tracer) are indeed close. The

fact that the tracer determined velocity is higher is not

surprising as it is expected to be the higher of the two

velocities. The reason for this is that the tracer

velocity at Site l is calculated from the mean time

recorded at the West Vent Shaft regulator where all the

air from the 2 Drill level is exhausted to the main

surface fan. This, of course, includes the air travelling

through the Northern drives (ie. through the 2/1, 2/2,

2/3, 2/4 and 2/5) with the determined velocity (by

anemometer) of 0.4 m/s total (Table 4.2). Assuming

an algebraic summation of the flows, then the tracer

velocity becomes 1.43 m/s. This value is therefore not

too different from the anemomter value of 1.53 m/s and

for actual underground conditions the agreement may be

regarded as excellent.

To summarise, the distinction between traditional and

tracer methods is most succinctly expressed by saying

that traditional methods measure how much air flows

whereas tracer methods measure how it does flow.

114

CHAPTER 5

SIGNIFICANCE OF RESULTS

In the introduction (Sect 1.0) it was stated that for the

essential functions of the ventilating air to be

satisfied (1) then an understanding of the behaviour of

ventilating air in actual roadways is necessary. It was

also stated that this cannot be done by the traditional

methods but it can be done by the tracer methods. Knowing

how the air flows, rather than simply how much air flows,

allows the calculation of these factors.

The tracer results presented in this thesis characterize

the behaviour of the ventilating air in an actual

underground mine roadway. These measured characteristics

of the ventilating air are the property of the

ventilating air itself for the regulator settings used.

These properties would probably apply for a range of

other settings also as the properties of the tracer used,

particularly its density, matched that of air very

closely, as is evident from Table 3.1. In fact, the

tracer selection was given considerable attention at the

outset to ensure the closest similarity possible with the

practical requirements of ease of detection, of cost and

of safety.

115

Hence the first significance of the results is that some

confidence can be placed in the conclusion that the

results represent those of the ventilating air and not of

the tracer. This is very important if an understanding of

the behaviour of ventilating air is to be obtained. Once

this close similarity has been recognised then a rational

basis would become available for considering the Vutukuri

and Lama (1) essential functions, viz. whether the

dilutions of the various substances to statutory levels

are met, and if not then what can be done for these

levels to be met.

5.1 THEORETICAL ASPECTS

The results of the present work clearly indicate a flow

layering, ie. flow regions that are distinctly separate.

Of course, there is no sharp separation in a physical

sense, but a more or less diffuse intermediate region.

However, no matter how the situation is viewed

conceptually, the fact remains that the flow is layered

and this would have a concentration interaction effect on

dilution rates. In this thesis the term "flow tube" has

been used to express the experimentally observed results

of the air flow layering characteristics in actual

underground cond it i ons.

116

The latter, viz. that the results were obtained under

actual underground conditions in an operating mine is the

second significance of the results. This is considered to

be of particular value in theoretical and computer

simulation work for predicting the dilution of noxious or

undesirable substances in the mine air.

There have been a number of research programs of the

above kind reported in the literature and they have been

reviewed recently by Bandopadhyay and Ramani (75) in

connection with their own work on the modelling of the

dispersion of diesel exhaust fumes.

In the above study Bandopadhyay and Ramani (75) adopted a

generalized mass transfer model, viz.:

£C at

d_ ax x a^ + dy E

£c y dy

+

, .ac , ^ c - u(x)3£ - v(y)gy

, .ac w^al

az z az

X(x,y,z,c) + jf(x,y,z,t) (5.1)

Where E , according to the authors are turbulent x,y, z

dispersion coefficients in x,y and z directions, >v is a

generalized decay coefficient for the pollutant and

r"(x,y,z,t) is the source term for the pollutant in the

roadway.

117

Equation (5.1) being a non-linear partial differential

equation with non-homogeneous terms had to be solved with

a number of assumptions and initial conditions,as well as

boundary conditions. The results of the calculations did

not match the reality very well.

It is of interest to note that in an earlier

investigation of the above question in the USSR Skobunov

(76) summarized the situation as follows:

"It must be evidently admitted that

mathematical models of physico-technical

ventilation systems give discrepancies of

magnitudes that in addition to being

unacceptable are very dangerous to safety."

In commenting on the disparity between computed and

measured results Bandopadhyay and Ramani (75) concluded

that:

"It is necessary to identify the existence of

the variations between model predicted and in

mine concentrations" and "It is important to

quantify the magnitude of the differences and

to identify the potential sources of their

origin. Only then can models be used as valid

predictions for more practical purposes"

118

The significance of the present results to the above

conclusions is that the foregoing mathematical

developments followed a mathematical model without due

regards to the assumptions of the model.

In short, mathematical modelling so far has assumed flow

conditions of the ventilating air that in reality may not

exist. The significance of the present results, obtained

in an actual operating mining environment, is that the

previous assumptions may be reconsidered in favour of

those that better represent the reality of actual mine

ventilation situations.

For example, from this study and taking the results of

Site 1 (Table A5) the dilution of a substance is shown in

Fig 5.1. This figure gives the mean value of the variance

for each node position obtained from Table A5 and the

calculated maximum concentration of the substance where

the initial concentration was 100%. The calculations for

CWAV were performed by the method of Fig 3.31.

The results in Fig 5.1 show that depending on the

position at which the air sample is taken so a different

resultant concentration of the substance would be

recorded. On the other hand, if a whole section is

sampled, then a mean value of 64.6% would be obtained.

118A

klB.l) jff.B) 48

.(H.9)

71

.(7.2)

57

61

\ 6 1

Jll.2)

(11.3)

77

71

74

.(7.9)

X7.5)

62

62

66

(10.5) U.

(10.3)

^a.v)

(0.2)

1(12-^ ••"•"Ji

57

24

44

(69.8)

J20.8)

.(o.i)

99 99 s 2 3

X

Fig. 5.1: Calculated Variances () and Residual Concentrations %. Site 1 calculated responses.

119

However, there will still be regions at this section with

concentrations below and above this value which may be

potentially hazardous.

The above calculations exclude mass transfer in the

direction normal to the flow. If required, this may be

done readily by, for example, a Fickian term (Sect 2.3.1)

and if flow velocity is assumed constant then dt and dL

terms are related, hence:

^ = D dL eff

dC d(z,y) (5.2)

Making a reasonable assumption that the concentration

gradient corresponds to a log mean concentration

difference (Ac)_ , then after integration of eqn (5.2)

and collecting terms the resultant expression is:

D ff £-= 1 -X- (AC)lmL (5.3) o o

With known values of D ff and (Ac), it should then be

possible to calculate the decrease of concentration for

given values of L due to mass transfer in the direction

normal to the flow. For molecular diffusion only (See Fig

2.11) D ff becomes simply DM- If eddying is present in

the transfer direction then D e^ should include the eff

contribution of this mechanism also, ie. terms such as E Y and E of eqn (5.1).

120

However, with dusts and gases of different density to

air, coupled phenomena have to be taken into account. In

other words, transport of species in the direction normal

to the flow is governed by the suimultaneous action of

the concentration driving force (eqn (5.2)) and the

gravitational (buoyancy) force. Interactions of this kind

were outside the scope of this thesis, but it is obvious

that future research should address such coupled

phenomena. Moreover, the results of this work indicate

that a model for the flow of the ventilating air should

also include some features of the convection model (Sect

2.2.3) in addition to the dominant features of the

dispersion model (Sect 2.5).

The above consideration of the significance of the

results have involved theoretical questions. These are

important since theory provides answers to how existing

operations may be improved as well as guidance to what

may be expected in new and untried situations.

121

5.2 PRACTICAL ASPECTS

The significance of the results from a practical point of

view are:

A recognition of the variability of the air flow, as

a certainty.

Here, the variability of the actual underground results

can be compared with the certainty of constancy of the

laboratory (Sect 4.1) and the large test rig (Sect 4.2)

results.

On the basis of Quantity surveys conducted as part of the

regular monitoring undertaken at the Elura Mine - along

with specific changes in the ventilation airflow noted in

this thesis (Sect 4.3.3) it is clear that local

variations in the flow do occur. This flow instabilities

appear to be common to all mine ventilation systems

where the flow velocities lie below some undetermined

critical velocity.

The certainty of change must be recognized and addressed

in all ventilation design work. The extent of the

expected variability should be determined by the

traditional/tracer analysis of a specific area. The

observed level of variability can then be included as a

122

design guide for correct network implementation, ie. the

correct fans, stoppings, ducts etc.

The layered or "flow tube" character of the

ventilating air.

This feature of the flow can give rise to a number of

undesirable consequences, including:

the presence of high concentrations of contaminants in

return roadways at a considerable distance from

their source. Specifically methane released during

the mining of Coal could exist in significantly

higher concentrations than the general body level in

"flow tubes" defined by the geometry of the mining

layout.

the lack of dilution of Nitrous Oxide exhaust gases from

diesel engines. High N02 levels could then be

expected remote from operating equipment.

The implications of this phenomenon include a necessity

for revision of the approach made to the calculation of

"adequate" amounts of diluting air for known levels of

contaminants. Flow patterns in the vicinity of

123

contaminant sources may: (i) be inferred from the results

reported in this thesis; (ii) cause an unsafe

concentration of the contaminant to exist, and; (iii)

continue to exist in the ventilating air stream.

Confident applications of the tracer technique in

analysis and in trouble shooting in underground

ventilation problems.

Problems inherent in the provision and control of

ventilating air underground could be easily assessed and

identified through the use of tracer techniques. Problems

such as leaky ventilation structures and undesired

recirculation could be quickly identified using a tracer

technique. Additionally, the extent of bypassing or

recirculation would be given as a result of the

measurements.

Prior to the continued development of the tracer release

and detection system for the conduct of whole of mine

surveys (which will be possible with the development of a

tracer/detection system capable of reading to a very

small concentration) the technique could be applied to

smaller studies. Some of the bypassing problems which

could be addressed would include leakage through bins,

stoppings and excessively open regulators - and the

124

recirculation by auxilliary fans could readily be

conducted.

Finally, it may be suggested that the findings reported

in this work may stimulate a review of some of the

statutory requirements concerning sampling methods and

permissible levels of pollutant in the mine airways.

125

CHAPTER 6

CONCLUSIONS

The results of this study have shown that:

1. Dispersion Mechanics can be applied to mine

ventilation surveys to provide quantitative flow

patterns and effective dispersion data in the

ventilating air. This therefore confirms the

expectations in this regard proposed in 1984 from

the results of a laboratory scale hydraulic model of

a section of a coal mine (10).

2. The ventilating air in the 2 Drill level network in

Elura Mine is characterised by layered segregated

flow patterns. This result of a Dispersion Mechancis

study is also supported by the results of

traditional velocity surveys.

3. The single observed constant feature of the

ventilating air is its short time scale transient

behaviour. This therefore supports similar results

reported in the literautre (2-6,64).

4. Acetylene (C_H ) is a suitable and practical tracer

gas for ventilation studies in metalliferous mines.

5. The release and detection system developed and

tested in laboratory and in a large scale test rig,

126

was, with subsequent modifications for underground

conditions, found to be a satisfactory system and

suitable for a one-person operation.

Other conclusions which emerge from this study are that

consideration should be given to (i) introducing the

"constant variability" of the ventilating air into

network calculations and (ii) examining statuatory

regulations governing concentration levels of noxious

substances in the ventilating air and the sampling

methods used.

Future research should address the guestion of the

interaction between the "flow tube" character of the

ventilating air, observed in this study, and the dilution

of the explosive and toxic gases in mines - these being,

of course, the three essential functions of the

ventilating air (1).

127

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128

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130

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th

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Al - 1

APPENDIX 1

UNDERGROUND TRACER RESULTS

- i — I — < — 1 — i — I — i — 1 — i — | — i — | — i — | — i — | — i — | — r

C J L U

m LU

LU

> E

r^

U LU in

ta El

S El

(l-088) 11)3 (t-»««) (i)3

| • i ' i • i ' ! i | i | • | i | l | • I ' I ' I ' I • I • I ' I ' I ' I ' I '

C J U J C O L U

> cn a u

- i — i — i — i — < — i — • — i — > — i — • — i — ' — i — ' — i — ' ' '

C J L U tn

71

C9 CM

ca

( j _ o e 8 ) (1)3 (I-<>8«) (1)3

ta co

ta

m ;-ts 00

Tt

. ta tn

H CM

l_) UJ C) '—* UJ 3: t-t

H

Tj"

.-. LU > tc a u

.,.,.. •, — | — T — | — I — | 1 — | — I — | r — | 1 1 — i — | r -l 1 — i — | I — I — i 1 1 1 1 1 — • 1 — i 1 — i — I f

UJ z:

LU > cc n u

is ta

ta ta ta

(1-098) (1)3 (!-«••) (1)3

Cl

. E) tn

cs cu

w

LU z: t-H H

UJ > DC 3 (J

r ta

j- -,.-.,.. - r — , — , — , , — | 1 — | — i — | 1 1 — i j — l — | 1 — — p j i — ' — i — ' — r

ta ta V*

I

IS 01

ta 00

. ta r-, ta CO

•ts Ln

•

r-.

u LU in

LU S. t~t

in T .

LU

> tn 3 (J

ts ts El

IS IS

(1-0B«) (1)3 (I-088) (1)3

El

E- ta : in

mrrip|i|i|ipT.mi|r|i|l|i|i|i|i-ftr<l,IMtl,Tt'lllll'PI,|Mll,lll,lrr>TrTrr

UJ t\J tn w LU UJ tc E Z3 l-H U

; CM

7 IS

19 Tt

ts tn

BJ tn

'ta in

. El • t f

. E3 tn

El

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LU 3" M

1-

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tM

LU

> tn 3 CJ

^ T « El tM El ta

E3

(1-088) (1)3 (I-088) (1)3

o . • *

. El tn

, S3 tM

CJ LU m T 1

LU s .H

H

r »-. LU > CC 3 CJ

n | • i i i i i i | i | i i i i ' i i j ' l ' l ' l ' I ' l ' I ' l • l ' l •

in

E)

61

i • I • i i I i I ' I ' I • I ' I i I ' | • I ' I ' I ' I • I ' I ' I ' I ' I '

CJ oo LU TH tn w LU

> LU CC S =3 >-< U

ta ta

ts CM

El ta

(1-088) (1)3 (1-088) (1)3

in CM

CU

tt

"tri u LU in

LU X. I-H

• *

CM

UJ

tr. 3 U

:-EI

11 LU tn •—* LU z; M

m CM

tu > tc D u

ta ta

ta

r1

(l-°«8) (1)3 ll-088) (1)3

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in

cxl

a CU

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UJ > tc 3 U

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CM CS ta ts

El

(I-ot8) (1)3 n-»»») I D S

o

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> tc n u

- I — | — l — | — I 1 — I — | 1 — | 1 — | — I — | — I — | — I 1 r -

u cn UJ CM cn

tu

UJ > a:

a u

cs El

IS

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n

a (U

t-> tu cn *-J

UJ r t~t

to CM UJ

> IE n u

E) CS

-_ '. _

. r

u LU m

LU r n

r-IM UJ

> ac 3 U

I ' I ' I • I ' I ' I • I ' I ' I • I

ts

(t-o«t) (1)3

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i •

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3

u

CJ UJ in " UJ x; >-i

• *

tn UJ

> cc 3 CJ

a cn

. a CU

u LU in w

LU r M

m tn UJ

> tc 3 U

| — i — | — i — | — i — | — i — | — i — | — i — | — i — | — i — | — i — | — r

CS CS

ts E)

U-<>88) (1)3 H-088) (1)3

ta tn

is oo

o CU

CJ LU tn «_. , UJ E l-H

r-tn

ui > tc 3 U

T—r- -i—i—r i ' i

cs

u UJ tn UJ 3=

tn

UJ > tc 3 U

(1-088) (1)3 (1-08.) (1)3

-i—i—i—r-'—r

-ts El

*E1 01

"El in

-63 •tf

-ta tn

-si tM

u IU in

UJ 2:

Tf

UJ

CC 3

o

T—•—1—'—r—'—1—1 si

El ca

El in

. El

-*

. ta tn

ta CM

U LU tn

LU 11 l-H

H

r-•n-LU

> tc 3 U

El

El

(I-888) 11)3 ll-888) (1)3

E"E1 i tM

-El ; ta

—ta ; Ol

El Tf

, El

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A2 - 1

APPENDIX 2

TABULATED TRACER RESULTS

A2 - 2

TABLE Al Laboratory Test Results

Run Q t c2 u R D/UL D/ud (l/s) (s) (s ) (m/s) (-) (-) (-)

1 2 3 4 5 6 7 8 9 10 11 12

10 10 10 20 20 20 30 30 30 35 35 35

5.1 4.9 5.2 2.5 2.8 2.7 1.7 1.6 1.8 1.5 1.2 1.4

2.34 2.30 2.32 0.26 0.38 0.33 0.10 0.09 0.12 0.06 0.05 0.07

0.57 0.57 0.57 1.14 1.14 1.14 1.71 1.71 1.71 1.99 1.99 1.99

5. 5. 5. 1. 1. 1. 2. 2. 2. 2. 2. 2,

.1x10

.1x10

.lxl04

.4x10

.4xl04

.4xl04 ,oxio4 .0x10 .0xl04 .4x10^ .4xl04 .4x10

0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0, 0.

045 048 ,043 ,021 ,024 .023 .018 .017 .019 .015 .017 .017

0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0, 0,

,90 ,96 ,86 .42 .48 .46 .36 .34 .38 .30 .34 .34

TABLE A2 Large Test Rig Results Cross Sectional Injection

Run L Q Ah t & u R D/uL D/ud (m) (m/s) (mmH20) (s) (s ) (m/s) (-) (-) (-)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

10 10 10 10 10 10 10 17 17 17 24 24 24 24 24

0.83 1.77 2.01 2.89 3.68 4.32 1.93 1.89 2.78 1.85 2.02 2.83 1.78 3.65 0.96

2.5 12 14 27 40 55 14 24 42 22 36 60 . 31

101 10

7.51 3.43 3.04 2.30 1.55 1.26 3.15 5.58 3.96 5.73 7.65 5.46 8.65 4.01 15.63

2.53 0.53 0.42 0.24 0.11 0.07 0.44 0.81 0.41 0.87 0.95 0.46 1.25 0.23 3.74

1.30 2.78 3.16 4.54 5.79 6.80 3.03 2.97 4.37 2.90 3.17 4.45 2.80 5.74 1.51

7.8x10 1.7x10^ 1.9xl0„ 2.7x10^ 3.4x10,, 4.1x10^ 1.8xl05 1.8x10,, 2.6xl0„ 1.7x10 1.9xl05 2.7xl05 1.7x10,, 3.4xl05 9.0x10

0.022 0.021 0.023 0.023 0.023 0.022 0.022 0.013 0.013 0.013 0.008 0.007 0.008 0.007 0.008

0.25 0.23 0.22 0.21 0.21 0.23 0.24 0.25 0.25 0.25 0.23 0.21 0.22 0.19 0.21

A2 - 3

TABLE A3 Large Test Rig Results Point Injection

Run

1 2 3 4 5 6 7 8 9 10 11 12 13 14

L

(m)

24 24 24 24 24 24 10 10 10 10 17 17 17 17

Q (m/s)

1.82 3.02 4.47 3.71 0.93 2.24 0.78 1.65 2.36 3.18 0.95 1.81 3.02 3.11

Ah (mmH20)

29 81

178 122

8 45 2

10 21 38 6

21 58 61

t (S)

8.76 5.23 3.48 4.33 16.71 6.95 8.41 3.98 2.79 2.21 11.83 6.20 3.91 3.68

2

a 2

(s2)

1.37 0.48 0.26 0.45 6.43 1.04 3.45 0.75 0.39 0.21 4.18 1.06 0.46 0.43

U

(m/s)

2.86 4.75 7.03 5.83 1.56 3.53 1.23 2.59 3.71 5.00 1.49 2.84 4.75 4.89

R

(")

1.6x10° 2.8xl05 4.2xl0„ 3.5xl04 8.4xl05 2.1x10 7.2xl0„ 1.6x10^ 2.2x10^ 3.5xl05 9.0xl0„ 1.7xl05 2.8xl05 2.9x10

D/uL (-)

0.009 0.009 0.010 0.009 0.011 0.011 0.024 0.023 0.024 0.022 0.015 0.014 0.015 0.016

D/ud (-)

0.25 0.24 0.27 0.24 0.29 0.29 0.27 0.26 0.27 0.24 0.28 0.26 0.26 0.30

TABLE A4 - 2/8 Results

Test Len u m M C . t „ meas No.

ct

1 2 5 6 12 13 14 15 17 18 20 21 22 23 24 25

P

(s) (s)

u , D/uL Reynolds D/ud d .p

C S lC ,T_ etc

No. (s ) (m/s) (-) (-) (-) (m)

3 0.25 8.1 0.18 6 0.25 16.3 3.19 9 0.27 23.8 4. 15 0.27 12.9 45.8 1, 5 0.84 6.6 3, 5 0.84 5.8 3

10 0.84 11.4 3, 10 0.81 12.6 15 0.81 18.3 15 0.81 18.6 22.5 20 0.86 24.8 20 0.86 21.2 24.1 20 0.86 28.8 19.2 3 0.45 5.2 3 0.45 5.8 5 0.45 10.3

53 00 05 30 90

5.08 6.70 6.23 0.12 5.39 11.61 0.69 1.95 0.58 1.48 0.52 0.85 0.49

0.37 0.37 0.38 1.16 0.76 0.86 0.88 0.79 0.82 0.81 0.81 0.94

0.001 8.2E+04 0.002 0.02 0.006 8.2E+04 0.005 0.16 0.004 8.9E+04 0.002 0.16 0.003 8.9E+04 0.001 0.20 0.035 2.8E+05 0.035 0.80 0.049 2.8E+05 0.049 1.11 0.015 2.8E+05 0.007 0.68 0.016 2.7E+05 0.008 0.73 0.010 2.7E+05 0.003 0.68 0.009 2.7E+05 0.003 0.61 1E-04 2.8E+05 0.000 0.01 0.006 2.8E+05 0.001 0.55 0.007 2.8E+05 0.002 0.64 0.036 1.5E+05 0.060 0.49 0.022 1.5E+05 0.036 0.30 0.004 1.5E+05 0.004 0.09

A2 - 4

TABLE A4 - 2/8 Results

(continued)

Test No.

26 27 28 29 34 35 36 37 39 40 43 44

Len

5 5 5

10 10 15 15 15 20 20 25 35

U t meas

0.39 0.39 0.39 0.48 0.48 0.48 0.44 0.44 0.44 0.44 0.46 0.46

(S)

9.7 11.2 10.4 18.6 17.3 26.5 27.4 24.0 34.1 35.6 42.5 65.2

t P

(S)

36.6 35.9 46.4

2

a 2

(s )

2.45 6.27 5.84 5.54 6.58 9.83 21.02 6.91 6.98 10.14 14.45 17.00

calc

(m/s)

0.52 0.45 0.48 0.54 0.58

-----

0.541 0.353

D/uL Reynolds D/ud No.

(")

0.013 0.025 0.027 0.008 0.011 0.007 0.014 0.006 0.003 0.004 0.004 0.002

(")

1.3E+05 1.3E+05 1.3E+05 1.6E+05 1.6E+05 1.6E+05 1.4E+05 1.4E+05 1.4E+05 1.4E+05 1.5E+05 1.5E+05

(")

0.013 0.025 0.027 0.004 0.005 0.002 0.005 0.002 0.001 0.001 0.001 0.000

d e ff

(m)

0.30 0.57 0.61 0.36 0.50 0.48 0.95 0.41 0.27 0.36 0.45 0.32

NB. t indicates the mean time for the parallel peak of the tr

trace if present.

A2 - 5

TABLE A5 - Site 1 Results; Positional Release

Test No.

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115

Cord

x,y

1/1 2,1 3,1 1,1 1,2 1,3 1/4 3,2 3,3 3,4 2,4 2,3 2,2 4,2 4,2 4,2 4,2 1,3 1/4 4,4 4,3 2,1 1/1 1,2 1,3 1/4 3,1 3,2 3,3 3,1 3,2 3,3 2,1 2,2 2,3 2,4 4,1 4,2 4,3 4,4 2,4 3,4 1/4 4,4 2,4 3,4 3,4 3,4 2,4 3,4 3,3

t s

(s)

13.5 12.9 11.2

-—

13.9 10.4

--

10.6 12.3

-

7.1 8.4 —

11.7 17.6

---

-

--

—

9.5 8.2

11.5 9.2

10.8 12.1 13.3 15.5

-

-

16.1 -

----

—

13.1 --

18.6 19.1 16.5

—

—

c2

(s2)

21.83 5.92 1.10

— —

6.57 0.93

— —

9.44 16.34

-

8.47 0.06

-

0.19 0.08

— — —

-

---

1.41 0.17

13.49 0.04 8.40 0.70 2.02 0.25

-

-

6.74 -

- • --

-

-

0.48 —

-

26.29 112.36 20.15

-

-

calc (m/s)

1.704 1.783 2.054

_ _

1.655 2.212

— —

2.170 1.870

—

3.239 2.738

-

1.966 1.307

— — —

—

— —

-

2.421 2.805 2.000 2.500 2.130 1.901 1.729 1.484

-

-

1.429 -

---

-

-

1.756 —

-

1.237 1.204 1.394

— —

D/uL

(")

0.060 0.018 0.004

_ _

0.017 0.004

_ _

0.042 0.054

—

0.084 0.000

—

0.001 0.000

— — —

—

— —

—

0.008 0.001 0.051 0.000 0.036 0.002 0.006 0.001

-

-

0.013 -

--

-

-

-

0.001 -

—

0.038 0.154 0.037

— _

D/ud

(")

0.276 0.082 0.020

—_ _

0.078 0.020

— _

0.193 0.248

0.386 0.002

—

0.003 0.001

— — —

—

— —

-

0.036 0.006 0.235 0.001 0.166 0.011 0.026 0.002

-

—

0.060 —

-— -

-

-

0.006 —

—

0.175 0.708 0.170

— _

cal (m)

6.26 1.86 0.46

1.78 0.45

4.39 5.65

8.78 0.04

0.07 0.01

0.82 0.13 5.33 0.03 3.76 0.25 0.60 0.05

1.36

0.15

3.97 16.10 3.87

A2 - 6

TABLE A5 - Site 1 Results; Positional Release (continued)

Test No.

116 117 118 119 120 154 156 157 158 165 166 171

Cord

x,y

3,3 4,1 2,1 3,1 1,1 4,4 4,3 1,1 4,2 4,4 4,3 1,2

t s

(s)

—

18.2 22.9

-

-

13.2 11.9 16.4 8.5

11.6 9.2

13.8

Cf2

(s )

—

30.47 9.44

—

-

12.89 11.05 6.46 0.16 0.43 5.25 0.76

calc (m/s)

_

1.264 1.004

—

—

1.742 1.933 1.402 2.706 1.983 2.500 1.667

D/uL

(-)

wm.

0.046 0.009

—

—

0.037 0.039 0.012 0.001 0.002 0.031 0.002

D/ud

(-)

__

0.212 0.041

—

—

0.170 0.179 0.055 0.005 0.007 0.143 0.009

d -, calc (m)

4.81 0.94

3.87 4.08 1.25 0.12 0.17 3.24 0.21

Head Posn.

CU L L L L L L R L L L C

TABLE A6 - Site 2 Results; Positional Release

Test No.

Cord

x,y

t s

(s) / 2* (s )

u calc (m/s)

D/uL

(-)

D/ud

(")

calc (m)

121 122 123 140 141 142 143 144 145 146 147 148 149 150 151 152 153 155 173 174 182

4,1 4,2 4,3 4,1 4,2 4,3 3,1 3,1 3,2 3,3 2,1 2,2 2,3 1,1 1,2 1,2 1,3 3,2 2,2 2,3 2,3

46.0 0.97 1.51

57.2 549.67 1.22

36.3 250.36 1.92 41.5 34^45 1.68 37.1 0.02 1.88

0.000

0.084

0.095 0.010 0.000

0.003 0.07

1.169 26.57

1.322 30.05 0.139 3.16 0.000 0.00

A2 - 7

TABLE A7 - Site 3 Results; Positional Release

Test No.

124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139

Cord

X/Y

4,1 4,1 4,1 4,2 4,3 3,1 3,1 3,2 3,3 2,1 2,2 2,3 1,1 1,1 1,2 1,3

t S

(s)

48.3 49.6

---

43.4 41.2 37.1

-39.5 40.1

--

45.3 -—

a2

i 2,

(s )

60.66 34.93

---

34.28 16.30 0.25

-3.06 0.48

--

4.51 -—

calc (m/s)

1.44 1.40

-— -

1.60 1.69 1.88

-1.76 1.74

--

1.54 -—

D/UL

(-)

0.013 0.007

— — -

0.009 0.005 0.000

0.001 0.000

--

0.001 -—

D/ud

(")

0.181 0.099

_ — —

0.127 0.067 0.001

-

0.014 0.002

--

0.015 -—

calc (m)

4.11 2.25

— _ —

2.88 1.52 0.03

-

0.31 0.05

--

0.35 -—

TABLE A8 - Site 4 Results; Positional Release

Test

No.

183 184 185 186 187 188 189 190 191

Cord

x,y

2,3 4,1 3,2 2,2 1/1 4,1 3,1 2,1 1,1

t s

(s)

80.9 101.3 82.2 54.8 80.3 118.2 91.3 70.2 66.8

a2

i 2,

(s )

52.358 51.308 41.892 198.20 27.082 64.268 58.350 98.561 33.021

calc (m/s)

0.860 0.687 0.847 1.270 0.867 0.589 0.762 0.991 1.042

D/uL

(")

0.0040 0.0025 0.0031 0.0330 0.0021 0.0023 0.0035 0.0100 0.0037

D/ud

(-)

0.0557 0.0348 0.0432 0.4594 0.0292 0.0320 0.0487 0.1392 0.0515

calc (m)

1.265 0.791 0.981 10.44 0.664 0.728 1.107 3.164 1.171

A3 - 1

APPENDIX 3

SITE ANEMOMETER RESULTS

A3 - 2

TABLE A9: site 1, Anemometer Positional Velocities

Position u, VL - *. low hxgh

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2.2 2,3 2,4 1,1 1,2 1,3 1/4

1.172 1.172 1.042 0.846 1.205 1.14

1.079 0.96

1.074 0.878 1.137 0.951 0.951 0.486 0.682 0.633

1.75 1.83 1.37 0.96 1.71 1.87 1.82 1.61 1.83 1.53 1.82 1.80 1.61 1.05 1.22 0.75

Average 0.963 1.532

TABLE A10 - Site 2, Anemometer Positional velocities

tion

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2.2 2,3 2,4

1/1 1,2 1,3 1,4

U-. u, . . low high

0.456 0.331 0.17 0.18

0.549 0.393 0.465 0.218 0.568 0.584 0.582 0.504 0.584 0.599 0.532 0.155

0.731 0.525 0^284 0.281 0.885 0.648 0.734 0.341 0.925 0.731 0.957 0.791 0.921 0.969 0.877 0.288

Averages 0.429 0.680

A3 - 3

TABLE All: Site 3, Anemometer Positional Velocities

low high

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2.2 2,3 2,4 1,1 1,2 1,3 1,4

0.538 0.566 0.582 0.399 0.442 0.445 0.538 0.532 0.46 0.46

0.398 0.471 0.429 0.465 0.472 0.448

0.875 0.884 0.931 0.657 0.701 0.703 0.811 0.875 0.745 0.751 0.639 0.764 0.691 0.728 0.775 0.718

Averages 0.477 0.765

TABLE A12: Site 4, Anemometer Positional Velocities

high

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2.2 2,3 2,4 1,1 1,2 1,3 1,4

0.210 0.159 0.159 0.110 0.257 0.159 0.240 0.262 0.257 0.175 0.164 0.119 0.240 0.248 0.235 0.257

0.318 0.268 0.275 0.161 0.501 0.224 0.361 0.402 0.409 0.288 0.275 0.180 0.399 0.316 0.392 0.486

Average 0.203 0.328

A3 - 4

TABLE A13: Site 5, Anemometer Positional Velocities

Position

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2.2 2,3 2,4 1,1 1,2 1,3 1,4

Average

low

0.201 0.148 0.221 0.184 0.301 0.184 0.221 0.164 0.201 0.195 0.224 0.201 0.194 0.162 0.201 0.215

0.201

high

0.339 0.218 0.327 0.284 0.488 0.239 0.320 0.213 0.365 0.347 0.347 0.388 0.353 0.273 0.339 0.341

0.324

TABLE A14: Site 6, Anemometer Positional Velocities

Position

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2,2 2,3 2,4 1,1 1,2 1,3 1,4

low

0.123 0.088 0.060 0.250 0.098 0.268 0.410 0.541 0.499 1.304 0.964 1.415 0.763 0.672 0.840 0.493

high

0.191 0.151 0.113 0.354 0.123 0.448 0.667 0.815 0.852 2.423 1.486 2.188 1.451 0.994 1.276 0.751

Average 0.549 0.893

A3 - 5

TABLE A15: Site 7, Anemometer Positional Velocities

Position

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2,2 2,3 2,4 1/1 1,2 1,3 1/4

Average

low

2.230 2.109 2.049 1.817 2.049 1.963 2.161 0.174 1.950 1.973 1.889 1.672 1.851 1.721 1.431 1.252

1.768

high

3.461 3.476 3.333 2.805 3.318 3.224 3.468 0.265 3.155 3.184 3.164 2.675 2.964 2.751 2.281 2.015

2.846

TABLE A16: Site 8, Anemometer Positional Velocities

Position u, „ u, . . low high

4,1 4,2 4,3 4,4 3,1 3,2 3,3 3,4 2,1 2,2 2,3 2,4 1,1 1,2 1,3 1,4

3.460 3.799 3.203 2.578 2.435 2.261 2.475 2.894 1.170 1.416 1.558 2.043 1.008 1.160 1.543 1.199

4.951 4.842 4.154 4.052 3.994 3.815 3.990 4.516 2.164 2.431 2.164 3.468 1.846 1.973 2.611 2.073

Average 2.138 3.315

A4 - 1

APPENDIX 4

COMPARATIVE SURFACE DATA REPRESENTATION

A4 - 2

Figures A4-1 and A4-2 detail the results of two separate

smoothing systems. Figure A4-1 shows the results obtained

where no smoothing was invoked during grid preparation in

the Plotcall program. The "spiky" nature of the results

and the tendency of the central areas to approach zero,

reduce the suitability of this smoothing regime.

Figure A4-2 shows the results obtained where 0.90

smoothing was invoked. Under this regime all of the

influence of the lower and higher readings obtained at

the positions across the drive section has been smoothed

out. This final shape is "too" perfect for use in drawing

comparisons with tracer results. Additionally evidence on

"flow tubes" returned from the tracer results, and

the surety of a convection flow regime discount this

extent of smoothing.

The final adopted system of 0.99 smoothing combines the

benefits of both these extents of smoothing in giving a

valuable representation of the velocity profile data.

A4 - 3

Fig A4-1: Site 1 results - 1.00 smoothing,

iWVWSy

mmw

Fig. A4-2: Site 1 results - 0.90 smoothing,