ABSTRACT

This experiment is carried out to investigate the characteristic of the flow of the liquid in the pipe which is also used to determine the Reynolds number for each flow state. The apparatus was solely designed for the study of the characteristic of the flow of fluid in pipe, the manners of flow and to calculate the range for laminar and turbulent flow where Reynolds number formula is used to prove the calculation between the fluid’s velocity, diameter of pipe and kinematic viscosity where Reynolds number is dimensionless.

Calculation was made from the data collected to estimate the range of laminar and turbulent flow. The calculation was by using the appropriate units and formula to prove that Reynolds number is dimensionless.

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TABLE OF CONTENTS

Abstract……………………………………………………………………………… 1

Table of Contents…………………………………………………………………… 2

Introduction…………………………………………………………………………… 3

Objectives……………………………………………………………………………. 4

Theory………………………………………………………………………………… 5

Description of Apparatus…………………………………………………………… 8

Experimental Procedures…………………………………………………………… 9

Results………………………………………………………………………………. 11

Sample calculation…………………………………………………………………...13

Discussion……………………………………………………………………………. 14

Conclusion…………………………………………………………………………… 15

Recommendation…………………………………………………………………… 16

References……………………………………………………………………………16

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INTRODUCTION

The criterion of laminar, transitional and turbulent flow can be known through

SOLTEQ Osborne Reynold’s Demonstration (Model: FM 11). In fluids mechanics,

internal flow is defined as a flow for which the fluid is confined by a surface.

The Osborne Reynolds device consists of water resource for the system supply, fix-

head water input to big and small transparent pipes, dye input by injection units, and

water output units to determine water flow rate. The laminar, transition and turbulent

flows can be obtained by varying the water flow rate using the water outlet control

valve. Water flow rate and hence the flow velocity is measured by volumetric

measuring tank. Flow pattern are visualized using dye injection through a needle

valve. The dye injection rate can be controlled and adjusted to improve the quality of

flow patterns.

OBJECTIVES

To monitor the different types of flow of laminar, transitional and turbulent through

different value of flow rate

For experiment A:

- To compute Reynolds’ number (R)

- To observe the laminar, transitional and turbulent flow.

For experiment B:

- To determine Reynolds’ number (R)

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- To determine the upper and lower critical velocities at transitional flow

THEORY

The Reynolds number is a widely used dimensionless parameters in fluids

mechanics.

Reynolds number formula: R = ULV

R = Reynolds number

U = Fluid velocity (m/s)

L = Characteristic length or diameter (m)

V = Kinematic viscosity (m2/s)

Reynolds number R is independent of pressure

The dimensionless parameter R is called Reynolds number. It is a ratio of the inertial

force to the viscous damping force. As R increase, the inertial force grow relatively

larger and the flow gets destabilized into full-blown turbulence.

The Reynolds experiment determines the critical Reynolds number at which laminar

flow becomes transitional and transitional flow becomes turbulent. The advantage of

using a critical Reynolds number, instead of a critical velocity, is that the result of the

experiment are applicable to all Newtonian fluids flow in round pipes of all diameters.

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Pipe flow conditions

For water flowing in pipe or circular conduits, L is the diameter of the pipe. For

Reynolds number less than 2100, the pipe flow will be laminar. For Reynolds number

from 2100 to 4000 the pipe flow will be considered a transitional flow. Turbulent occur

when Reynolds number is above 4000. The viscosity of the fluid is also determines

the characteristic of the following becoming laminar or turbulent. Fluids with higher

viscosity are easier to achieve a turbulent flow condition. The viscosity of the fluid

also depends on the temperature.

Laminar flow

Laminar flow denoted a steady flow condition where all streamlines follow parallel

paths, there being no interaction (mixing) between shear planes. Under this

conditions the dye observed will remains as a solid, straight and easily identifiable

component of flow.

Transitional flow

Transitional flow is a mixture of laminar and turbulent flow with turbulence in the

centre of the pipe and laminar flow over the edges. Each of these flow behaves in

different manners in term of their frictional energy loss while flowing and have

different equations that predict their behaviour.

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Turbulent flow

Turbulent flow denoted an unsteady flow condition where streamlines interact

causing shear plane collapse and mixing of the fluids. In this condition the dye

observed will become disperse in the water and mix with water. The observed dye

will not be identifiable at this point.

DESCRIPTION OF APPARATUS

1. Dye reservoir

2. Dye control valve

3. Dye injection

4. Head tank

5. Observation tube

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6. Overflow tube

7. Water inlet valve

8. Bell mouth

9. Water outlet valve

EXPERIMENTAL PROCEDURES

EXPERIMENT A

1. The dye injector is lowered until it is seen in the glass tube.

2. Inlet valve, V1 is opened and water is allowed to enter the stilling tank.

3. A small overflow spillage is ensured through the over flow tube to maintain a

constant level.

4. Water is allowed to settle for a few minutes.

5. Water is then flowed through the visualizing tube.

6. The dye control valve, V4 is slowly adjusted until a slow flow with dye injection

is achieved.

7. Water inlet valve, V1 and outlet valve, V2 is regulated until a straight

identifiable dye line is seen. Laminar flow is visible and a picture is captured

as a result.

8. The flow rate at the outlet valve, V2 is measured using volumetric method.

9. The experiment is repeated by regulating water inlet valve, V1 and outlet

valve, V2 to produce transitional and turbulent flow.

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EXPERIMENT B

1. The dye injector is lowered until it is seen in the glass tube.

2. Inlet valve, V1 is opened and water is allowed to enter stilling tank.

3. A small overflow of spillage is ensured through the over flow tube to maintain

a constant level.

4. Water is allowed to settle for a few minutes.

5. Water is flown through the visualizing tube.

6. The dye control valve, V4 is adjusted slowly until a slow flow with dye injection

is achieved.

7. The procedure is repeated to create a laminar flow; the flow rate is slowly

increased until the laminar flow produces a small disturbance or eddies.

8. The flow rate at the outlet valve, V2 is measured using volumetric result.

9. The experiment is repeated after introducing a turbulent flow and slowly

decrease flow rate till the flow become transitional. This is the upper critical

velocity

RESULTS

EXPERIMENT A

Flow type: Laminar

Volume (L) Time (s) Volume flow rate,

Q (m3/s)

Reynolds number

1 336 2.9762x10-6 243.36

1 330 3.0303x10-6 248.04

1 332 3.0120x10-6 246.48

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Flow type: Transitional

Volume (L) Time (s) Volume flow rate

(m3/s)

Reynolds number

2 208 9.6154x10-6 784.68

2 205 9.7561x10-6 795.60

2 200 1.000x10-5 815.88

Flow type: Turbulent

Volume (L) Time (s) Volume flow rate

(m3/s)

Reynolds number

3 82 3.6585x10-5 2985.84

3 80 3.7500x10-5 3060.72

3 84 3.5714x10-5 2915.64

EXPERIMENT B

Laminar -> Transitional

Volume (L) Time (s) Volume flow rate

(m3/s)

Reynolds number

1 123 8.1301x10-6 663.00

1 125 8.000x10-6 653.64

1 121 8.2645x10-6 673.92

Transitional -> Turbulent

Volume (L) Time (s) Volume flow rate

(m3/s)

Reynolds number

2 82 2.4390x10-5 1990.56

2 80 2.5000x10-5 2040.48

2 84 2.3810x10-5 1943.76

Glass tube diameter (d) = 0.0156m

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SAMPLE CALCULATION

Experiment A: Laminar

1L = 0.001m3

Q = m3/s

= 0.001 / 336

= 2.9762x10-6

A = πd2/4

= π(0.0156)2/4

= 1.9113x10-4

Q = VA

2.9762x10-6 = V(1.9113x10-4)

V = 0.0156 m/s

μ=¿ 0.001 kg/ms

D = 1000 kg

Re = ρVDμ

Re = 1000×0.0156×0.0156

0.001

Re = 243.36

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DISCUSSION

From experiment A, the average Reynolds number for the flow type of laminar,

transitional and turbulent is 245.96, 798.72 and 2987.4 respectively. It can be seen

that the Reynolds number obtained for transitional and turbulent flow is not within the

correct range.

Laminar flow Transitional flow Turbulent flow

For laminar flow, the dye injection shows a neat straight line in motion. In laminar

flow, there is less disruption therefore the particles are in tight and orderly manner.

For turbulent flow, the dye injection shows a scattered motion. When the flow rate

increase, it is more vigorous thus, it disrupts the blue dye and then indicates the

motion of turbulent flow. For transitional flow, the blue dye injection shows a

combination of laminar flow and turbulent flow. It would start with a straight orderly

manner and would be more scattered towards the end.

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There is a transition period between laminar and turbulent flow which is lower critical

velocity and upper critical velocity. For lower critical velocity, it is the velocity at which

laminar flow stops and for upper critical velocity is where a turbulent flow starts. The

Reynolds number for upper critical velocity is in the range of 2700 and 4000, just

about before entering turbulent flow which is 4000.

CONCLUSION

From the results obtained, it can be seen that the Reynolds number obtained from

experiment A and B does not obey Reynolds number for turbulent. In fluid

mechanics, Reynolds number for laminar is stated as less than 2000 while Reynolds

number for turbulent is more than 4000 and transitional takes place in between 2000

and 4000.

For experiment A, in laminar, Reynolds number is achieved by getting an average of

245.96. For transitional, the average Reynolds number obtained is 798.72, which is

not in transitional region. While for turbulent, the average Reynolds number achieved

is 2987.4, also outside of the claimed turbulent region.

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RECOMMENDATION

Before injecting the dye into the fluids, we should make sure the dye is not too

much and not too insufficient. It will be hard to stable the fluids to get a laminar

flow

For a better result, make sure the water is clear because using clear water is

easier to observe the results and less discrepancy in the water.

The person collecting the water should synchronize well the time keeper.

The experiment should be done repeatedly to get a more stable result and is

then averaged.

REFERENCES

Fluids mechanics by Dr. Andrew Sleigh (J. Franzini/ E. Finnemore), McGraw

Hill.

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