TOPIC 6: OSBORNE REYNOLDS DEMONSTRATION

6.1 THEORY

The theory is named in honour of Osborne Reynolds, a British engineer who

discovers the variables that can be used as a criterion to distinguish between

laminar and turbulent flow.

The Reynolds number is widely used dimensionless parameters in fluid

mechanics.

Reynolds number formula:

R = VLv

Where; R = Reynolds number

V = Fluid velocity (m/s)

L = characteristic length or diameter (m)

v = Kinematic viscosity (m2/s)

Reynolds number R is independent of pressure, P.

6.2 APPARATUS:

The Osborne Reynolds Demonstration apparatus is equipped with a

visualization tube for students to observe the flow condition. The rock inside the

stilling tank are to calm the inflow water so that there will not be any turbulence to

interfere with the experiment. The water inlet/outlet valve and dye injector are

utilized to generate the required flow.

1 Dye reservoir 2 Dye injector

3 Stilling tank 4 Observation tube

5 Water inlet valve 6 Bell mouth

7 Water outlet valve 8 Overflow tube

6.3 MAINTENANCE AND SAFETY PRECAUTIONS

1. Place the unit on a level ground.

2. Beware with the observation tube.

6.4 EXPERIMENTAL PROCEDURES

6.4.1 Experiment 1: Observation of Flow Regimes

Objective

To compute Reynolds number and to observe the laminar, transitional and

turbulent flow.

Procedures

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

2. The inlet valve is opened and water is allowed to enter the stilling tank.

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

maintain a constant level.

4. The flow control valve is opened fractionally to let water flow through

the visualizing tube.

5. The dye control needle valve is slowly adjusted until a slow flow with

dye injection is achieved.

6. The water inlet and outlet valve are regulated until an identifiable dye

line is achieved. The type of the flow is identified and the picture of

the flow is taken.

7. The flow rate is measured.

8. The experiment is repeated to produce a few different types of flow.

9. The development of different flow in pipe is discussed.

6.4.2 Experiment 2: Loss Coefficient

Objective

To determine the Reynolds number and to determine the upper and lower

critical velocities at transitional flow.

Procedures

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

2. The inlet valve is opened and water is allowed to enter stilling tank.

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

maintain a constant level.

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

5. The flow control valve is opened fractionally to let water flow through

the visualizing tube.

6. The dye control needle valve is slowly adjusted until flow with dye

injection is achieved.

7. Small disturbance or eddied are produced to determine the lower

critical velocity.

8. The experiment is repeated by first introducing a turbulent flow and

produce the laminar flow to determine the upper critical velocity.

9. The findings from the results are summarized.

B) RESULTS, DISCUSSION, CONCLUSION, OPEN ENDED QUESTIONS,

REFERENCES

Name: Mohammad Iskandar Zulkarnain b. Roslan Matric No. : 42188

7. RESULTS

7.1 Experiment 1: Observation of Flow Regimes

Volume of water: 1L = 1 x 10-3 m3/s

Temperature = 270C

Diameter of the observation tube, D = 15.6 x10-3 m

Area of the observation tube, A = π4

D2

= 1.9113 x 10-4 m2

Flow t1 (s) t2 (s) t3 (s)

average

t (s)

Flow

rate, Q

(m3/s)

Laminar 119 80 72 90.33 1.1070 x

10-5

Transitio

n

62 60 63 61.67 1.6216 x

10-5

Turbulent 43 46 47 45.33 2.2059 x

10-5

SAMPLE CALCULATIONS

Volume flow rate, Q = Volume / time

For laminar flow,

Q = 1L / 90.33s

= 1.1070 x 10-5 m3/s

OBSERVATIONS

Laminar flow Transition flow

Turbulent flow

7.2 Experiment 2: Loss Coefficient

Forward (Laminar to Transition to Turbulent)

Flow

t1 (s) t2 (s) t3 (s) average

t (s)

Flow

rate, Q

(m3/s)

Fluid

velocity,

V (m/s)

Reynolds

number

Laminar 119 80 72 90.33 1.1070

x 10-5

0.05792 1058.02

Transitional 62 60 63 61.67 1.6216

x 10-5

0.08484 1549.77

Turbulent 43 46 47 45.33 2.2059

x 10-5

0.11541 2108.19

Backward (Turbulent to Transition to Laminar)

Flow t1 (s) t2 (s) t3 (s)

average

t (s)

Flow

rate, Q

(m3/s)

Fluid

velocity,

V (m/s)

Reynolds

number

Turbulent 44 46 47 45.67 2.1896

x 10-5

0.11456 2092.67

Transitional 64 60 63 62.33 1.6044

x 10-5

0.08394 1533.33

Laminar 80 72 72 74.67 1.3392

x 10-5

0.07007 1279.97

SAMPLE CALCULATIONS

Kinematic viscosity, v of water at 27oC = 8.54 x 10-7 m2/s

1. Forward

Laminar flow:

Velocity, V = Q/A

= (1.1070 x 10-5) / (1.9113 x 10-4 m2)

= 0.05792 m/s

Reynolds number, Re = VDv

= 0.05792 x 15.6E-3

8.54E-7

= 1058.02

2. Backward

Turbulent flow:

Velocity, V = Q/A

= (2.1896 x 10-5) / (1.9113 x 10-4 m2)

= 0.11456 m/s

Reynolds number, Re = VDv

= 0.11456 x15.6E-3

8.54E-7

= 2092.67

To determine upper and lower critical velocities,

1. Forward

Lower boundary

V = Q/A

= [1.6216 x 10-5] / [1.911 x 10-4]

= 0.08484 m/s

Upper boundary

V = Q/A

= [2.2059 x 10-5] / [1.911 x 10-4]

= 0.11541 m/s

2. Backward

Lower boundary

V = Q/A

= [1.6044 x 10-5] / [1.911 x 10-4]

= 0.08394 m/s

Upper boundary

V = Q/A

= [1.3392 x 10-5] / [1.911 x 10-4]

= 0.07007 m/s

Flow Upper boundary (m/s) Lower boundary (m/s)

Forward 0.11541 0.08484

Backward 0.07007 0.08394