Flowmeter Measurement _Experimental Manual.pdf

8/10/2019 Flowmeter Measurement _Experimental Manual.pdf

http://slidepdf.com/reader/full/flowmeter-measurement-experimental-manualpdf 1/17

SOLTEQ ® Flowmeter Measurement Apparatus (Model: FM 101)

1

1.0 INTRODUCTION

SOLTEQ ® Flowmeter Measurement Apparatus (Model: FM101) apparatus isdesigned to operate together with a basic hydraulic bench or any water supply. It is tofamiliarize the students with typical methods of flow measurement of an incompressible

fluid.

The apparatus is able to demonstrate the flow measurement comparison by using a venturidevice, orifice device and rotameter. The flow comparison can be further be used tocompare against the flow measurement of the hydraulics bench which can be either byGravimeteric or Volumetric Method, depending on the type of hydraulics bench in use.

Other features of the flow apparatus include a 90 degree elbow with pressure tappingsbefore and after this elbow. The purpose of these features is to provide an added functionto this apparatus to allow students to calculate the total head loss and loss coefficient whenfluid flows through these devices.

In short, the apparatus allows following range of experiment to be carried out:

a) Direct comparison of flow measurement using venturi, orifice, rotameter and bench.b) Determination of total head loss and loss coefficient of fluid flow through a 90 degree

elbow.c) Comparison of pressure drop against each device.




2

2.0 GENERAL DESCRIPTION

2.1 Sketch of apparatus and devices

Figure 1: Sketch of apparatus and devices




3

2.2 Part Identification

Figure 2: Part Identification Diagram

1. Manometer Tubes 6. Rotameter

2. Discharge Valve 7. 90° Elbow

3. Water Outlet 8. Orifice

4. Water Supply 9. Venturi 5. Staddle Valve

4

3

2

1

5

6

7

8

9




4

2.3 Specification of dimensions

i) Venturi meter

Figure 3: Specification of the Venturi Meter

Tapping A = 26 mmTapping B = 21.6 mmTapping C = 16 mmTapping D = 20 mmTapping E = 22 mmTapping F = 26 mm

ii) Orifice

Figure 4: Specification of the Orifice Plate

Orifice upstream diameter (G) =φ26 mmOrifice diameter (H) =φ16 mm

2.4 General Requirements

SOLTEQ ® Hydraulic Bench (Model: FM110)

CA D E FB

G H




5

3.0 SUMMARY OF THEORY

3.1 Rotameter

The rotameter is a flow meter in which a rotating free float is the indicating element.

Basically, a rotameter consists of a transparent tapered vertical tube through whichfluid flow upward. Within the tube is placed a freely suspended “float” of pump-bobshape. When there is no flow, the float rests on a stop at the bottom end. As flowcommences, the float rises until upward and buoyancy forces on it are balanced byits weight. The float rises only a short distance if the rate of flow is small, and viceversa. The points of equilibrium can be noted as a function of flow rate. With awell-calibrated marked glass tube, the level of the float becomes a direct measureof flow rate.

Figure 5: The Rotameter

3.2 Venturi Meter

The venturi meter consists of a venturi tube and a suitable differential pressuregauge. The venturi tube has a converging portion, a throat and a diverging portionas shown in the figure below. The function of the converging portion is to increasethe velocity of the fluid and lower its static pressure. A pressure differencebetween inlet and throat is thus developed, which pressure difference is correlatedwith the rate of discharge. The diverging cone serves to change the area of thestream back to the entrance area and convert velocity head into pressure head.

Figure 6: Venturi Meter

Tapered tube

Flow

Scale

1 2

Inlet

Throat




6

Assume incompressible flow and no frictional losses, from Bernoulli’s Equation

2

222

1

211

22Z

g v p

Z g

v p++=++

γ γ ………………….…………………………...(1)

Use of the continuity Equation Q = A1V1 = A2V2, equation (1) becomes

−=−+

−2

1

22

221 1

221

A A

g V

Z Z p p

γ ………………….…………………...(2)

Ideal21

21

212

1

2

222

2121

//

−+

−

−==

−

Z Z p p

g A

A AV AQ

γ …………...…(3)

However, in the case of real fluid flow, the flow rate will be expected to be lessthan that given by equation (2) because of frictional effects and consequent headloss between inlet and throat. In metering practice, this non-ideality is accountedby insertion of an experimentally determined coefficient, Cd that is termed as thecoefficient of discharge. With Z1 = Z2 in this apparatus, equation (3) becomes

Actual21212

1

22

2121

−

−××=

−

γ

p pg

A

A ACd Q ……………..…. (4)

Hence,

( )[ ] 2121

212

/ 21 ρ PPg A At

At Cd q −

−××=

−

…………………....…. (5)

Where,Cd = Coefficient of discharge (0.98)D2 = Throat diameter = 16 mm

D1 = Inlet diameter = 26 mmAt = Throat area = 2.011 x 10-4 m2 A = Inlet area = 5.309 x 10-4 m2 g = 9.81 m/s2 ρ = Density of water = 1000 kg/m3 P1 = Inlet pressure (Pa)P2 = Throat pressure (Pa)




7

3.3 Orifice Meter

The orifice for use as a metering device in a pipeline consists of a concentricsquare-edged circular hole in a thin plate, which is clamped between the flanges ofthe pipe as shown in the figure below.

Figure 7: Orifice Meter

Pressure connections for attaching separate pressure gauges are made at holes in

the pipe walls on both side of the orifice plate. The downstream pressure tap isplaced at the minimum pressure position, which is assumed to be at the venacontracta. The centre of the inlet pressure tap is located between one-half and twopipe diameters from the upstream side of the orifice plate, usually a distance ofone pipe diameter is employed. Equation (4) for the venturi meter can also beapplied to the orifice meter where

Actual21

21

212

1

22 21

−

−××=

−

γ

p pg

A A

ACd Q ………………. (6)

The coefficient of discharge, Cd in the case of the orifice meter will be differentfrom that for the case of a venturi meter.

( )[ ] 2187

212

21 hhg A At

At Cd Q −

−××=

−

…………………………….(7)

Where,Cd = Coefficient of discharge (0.63)D7 = Orifice diameter = 16 mmD8 = Orifice upstream diameter = 26 mmAt = Orifice area = 2.011 x 10-4 m2 A = Orifice upstream area = 5.309 x 10-4 m2 (h7 – h8) = Pressure difference across orifice (m)

A1

A2




8

3.4 90o elbow

Figure below shows fluid flowing in a pipeline where there is some pipe fitting suchas bend or valve, and change in pipe diameter. Included in the figure is thevariation of piezometric head along the pipe run, as would be shown by numerous

pressure tappings at the pipe wall.

Figure 8: Piezometric head along a pipeline

If the upstream and downstream lines of linear friction gradient are extrapolated tothe plane of fitting, a loss of piezometric head,∆ h, due to the fitting is found. Byintroducing the velocity heads in the upstream and downstream runs of pipe, totalhead loss, ∆H can be determined in which

g V

g V

hH 22

22

21 −+∆=∆ ………………………………………………………………(8)

Energy losses are proportional to the velocity head of the fluid as it flows aroundan elbow, through an enlargement or contraction of the flow section, or through avalve. Experimental values for energy losses are usually expressed in terms of adimensionless loss coefficient K, where

g V H

or g V

H K

22 22

21 //

∆∆= ……………………………..…………………………………(9)

depending on the context.

V 22 / 2g

V12 / 2g

H

h

V 2V 1




9

For results of better accuracy, long sections of straight pipe are required toestablish with certainty the relative positions of the linear sections of thepiezometric lines. However, in a compact apparatus as described in this manual,only two piezometers are used, one placed upstream and the other downstream ofthe fitting, at sufficient distances as to avoid severe disturbances. These

piezometers measure the piezometric head loss, ∆ h’ between the tapping. Thus f hhh ∆−∆=∆ ' ……………………………..………………………………………(10)

Where

=∆g

V D L

f h f 24

2

Δ hf = friction head loss which would be incurred in fully developed flowalong the run of pipe between the piezometer tappings

f = friction factorL = distance between the piezometer, measured along the pipe center lineD = pipe diameterV = average velocity of fluid flow in pipe

The friction head loss is estimated by choosing a suitable value of friction factor, ffor fully developed flow along a smooth pipe. The method used in this manual todetermine the friction factor is the prandtl equation

( ) 4041

.Relog −= f f

…………………………………………………………(11)

Typical values derived from this equation are tabulated in the table below:

Re, x 104 0.5 1.0 1.5 2.0 2.5 3.0 3.5F, x 10-3 9.27 7.73 6.96 6.48 6.14 5.88 5.67

In determination of the fraction factor, f, it is sufficient to establish the value of f at just one typical flow rate, as about the middle of the range of measurement due tothe fact that f varies only slowly with Re, and the friction loss is generally fairlysmall in relation to the measured value of∆h’.




10

Characteristic of flow through elbow and at changes in diameter

90 o Elbow

Figure below shows flow round a 90o elbow which has a constant circular cross

section.

Figure 9: 90 o Elbow

The value of loss coefficient K is dependent on the ratio of the bend radius, R tothe pipe inside diameter D. As this ratio increase, the value of K will fall and viceversa.

gV K H 2 / 2×= …………………………………………………..……………(12)

Where,K = Coefficient of lossesV = Velocity of flowg = 9.81 m/s2

D V

R




12

Note:

If above methods fail, then you will now have to “flush” the system by “bleeding” toair out.

All that is required is the use of a small object such as pen or screw driver, todepress the staddle valve, found at the top right side of manometer board.

Depress staddle valve lightly to allow fluid and trapped air to escape out. (Takecare or you will wet yourself or the premise).

Allow sufficient time for bleeding until all bubbles escape.

Once all bubbles have been “bleed”, start to reduce the water supply now bymanipulating BOTH control valves, reducing first the flow apparatus dischargevalve and then the hydraulic bench valve in alternate motion, bringing down theDATUM level of the water in the manometer board.

(i) At this point you may start the experiment proper.(j) You are ONLY interested in the data obtained from tubes:

Probe A and C for venturi calculationProbe G and H for orifice calculationProbe I and J for 90 degree elbow calculation

All other probe readings are for viewing of pressure curve ONLY.

(k) With above guide, record water level of each probe at a certain flow. With theheight difference (∆h), use formula provided to calculate. Verify the resultsobtained against rotameter and hydraulic bench for experiment of flowmeasurement comparison.

(l) Complete experiment with other flow rates.




13

4.2 Demonstration of the operation and characteristic of three different basictypes of flowmeter

Objective:

To obtain the flow rate measurement by utilizing three basic types of flowmeasuring techniques; rotameter, venturi meter and orifice meter.

Procedures:

1. Place apparatus on bench, connect inlet pipe to bench supply and outlet pipeinto volumetric tank.

2. With the bench valve fully closed and the discharge valve fully opened, startup the pump supply from hydraulic bench.

3. Slowly open the bench valve until it is fully opened.4. When the flow in the pipe is steady and there is no trapped bubble, start to

close the bench valve to reduce the flow to the maximum measurable flow rate.5. By using the air bleed screw, adjust water level in the manometer board.

Retain maximum readings on manometers with the maximum measurable flowrate.

6. Note readings on manometers (A - J), rotameter and measured flow rate.7. Step 6 is repeated for different flow rates. The flow rates can be adjusted by

utilizing both bench valve and discharge valve.8. To demonstrate similar flow rates at different system static pressures, adjust

bench and flow control valve together. Adjusting manometer levels as required.




14

4.3 Determination of the loss coefficient when fluid flows through a 90 degreeelbow

Objective: To investigate the loss coefficient of fluid through 90 degree elbow.

Procedures:

1. Place apparatus on bench, connect inlet pipe to bench supply and outlet pipeinto volumetric tank.

2. With the bench valve fully closed and the discharge valve fully opened, startup the pump supply from hydraulic bench.

3. Slowly open the bench valve until it is fully opened.4. When the flow in the pipe is steady and there is no trapped bubble, start to

close the bench valve to reduce the flow to the maximum measurable flow rate.5. By using the air bleed screw, adjust the water level in the manometer board.

Retain maximum readings on manometers with the maximum measurable flowrate.

6. Note readings on manometers (I and J) and measured flow rate.7. Step 6 is repeated for different flow rates. The flow rates can be adjusted by

utilizing both bench valve and discharge valve.8. Complete the tables below.

9. Plot graph∆H againstg

V s2

2

for 90 degree elbow to determine the coefficient of

losses.




15

4.4 General Shut-down Procedures

1. Close water supply valve and venturi discharge valve.

2. Turn off the water supply pump.

3. Drain off water from the unit when not in use.




16

5.0 MAINTENANCE AND SAFETY PRECAUTIONS

1. It is important to drain all water from the apparatus when not in use. The apparatusshould be stored properly to prevent damage.

2. Any manometer tube, which does not fill with water or slow fill, indicates that tappingor connection of the manometer is blocked. To remove the obstacle, disconnect theflexible connection tube and blow through.

3. The apparatus should not be exposed to any shock and stresses.

4. Always wear protective clothing, shoes, helmet and goggles throughout thelaboratory session.

5. Always run the experiment after fully understand the unit and procedures.




17

6.0 REFERENCES

Applied Fluid Mechanics 5th Edition, Robert L. Mott, Prentice-Hall

Elementary Fluid Mechanics 7th Edition, Robert L. Street, Gary Z. Watters, John K.

Vennard, John Wiley & Sons Inc.

Fluid Mechanics 4th Edition, Reynold C. Binder

Fluid Mechanics with applications, Anthony Esposito, Prentice-Hall International Inc.

Flowmeter Measurement _Experimental Manual.pdf

Documents

Transcript of Flowmeter Measurement _Experimental Manual.pdf