ABSTRACT

Aims of this experiment is to observe the characteristic of the flow of fluid in pipe, which

may be laminar, transition or turbulent pipe flow by measuring the Reynolds number and the

behavior of the flow.

In order to determine that the flow is laminar, transitional, or turbulent, the value of

‘Reynolds number’ (Re) has to be determined. Laminar and turbulent flow are most common in

flow regimes or in liquid flow measurement operations but there is also transitional flow. If Re is

high (>4000), inertial forces dominate viscous forces and the flow is turbulent; if Re number is

low < 2300), viscous forces dominate and the flow is laminar. Other than that, the dye injections

that were supposed to be use in the experiment can clearly show the behavior of the flow, but it

cannot be used as the apparatus are running out of dye.

The experiment involves running the Osborne Reynolds equipment with different volume

flow rates of water. In this experiment we fix the volume, which is 4×10-3 m3. Time is taken

when the volume reached the fix volume. At the same time the characteristics of the flow are

observed whether it is laminar, transition and turbulent flow. From the data collected, calculation

is made to estimate the range for laminar, transition and turbulent flow. In proving that the

Reynolds number is dimensionless, the calculation is made by using the units only and using the

appropriate formula. It is proved that the Reynolds number is dimensionless.

APPARATUS

1. The F1-10 Hydraulics bench allow to measure flow by timed volume collection. (Figure

A)

Figure A: F1-10 Hydraulic Bench [1]

2. The F1-20 Reynolds’ Apparatus (Figure B)

Figure B: The F1-20 Reynolds’ Apparatus [2]

3. A stopwatch to allow us to determine the flow rate of water.

PROCEDURES

1. The Reynolds apparatus has been position on the fixed, vibration-free surface (not the

hydraulic bench) and the base had been ensure horizontal. This apparatus has been set up

by the technician before experiment start.

2. The pump started. System is allowed to fill with water by slightly open the apparatus

flow control valve, then the bench valve opened.

3. The bench control valve was adjusted to produce a low overflow rate to avoid the water

level reaches the overflow tube.

4. The initial height of water level in head tank is set to be 15.5 cm. This height is just for

reference level for the next procedure.

5. The flow increased by opening the apparatus flow control valve. Flow of the water let to

stabilize then level of water level in head tank recorded.

6. The collection of 4 liters of water in the volumetric tank is timed and recorded by closing

the ball valve which acts as a stopper to prevent the tank outflow.

7. The ball valve is re-opened after taking the measurements.

8. The experiment is repeated for another 3 varies height of water level.

CALCULATIONS

Flow Rate Qt,

Qt = V = Volume Collected

t Time for Collection

1 m3 = 1000 L

4 L = 0.004 m3

Qt = 0.004m3

66s

= 6.0606 × 10-5 m3/s

Velocity,

v = Flow Rate

Area of Pipe

Area of Pipe = 7.854 × 10-5 m2

v = 6.0606 × 10-5 m3/s

7.854 × 10-5 m2

= 0.7717 m/s

Reynolds number,

Reynolds Number, Re = velocity × diameter

Viscosity

At 25 ºC the kinematic viscosity of water is = 0.893 x 10-6 m2/s

Diameter = 0.01 m

Re = 0.7717 m/s s x 0.01m

0.893 x 10-6 m2/s

= 8641.6573

All data are repeatedly calculated for every time taken,

Laminar Flow: Re <2000

Transition Flow: 2000<Re<4000

Turbulent Flow: Re>4000

RESULTS

Table 1: Table of volume of water, time taken to collect the water, volume flow rate, velocity and

Reynold’s Number.

Volume

(L)

Volume

(m3)

Time (s) High

(cm)

Volume flow rate,

QT=V/t (m3/s)

Velocity, v=QT/A

(m/s)

Reynold's

number,

Re= vD/ν

4 0.004 66 16 6.0606 x 10-5 0.7717 8641.6573

4 0.004 35 16.4 1.1429 x 10-4 1.4552 16295.6327

4 0.004 25 16.7 1.6 x 10-4 2.0372 22812.9899

4 0.004 18 18.3 2.2222 x 10-4 2.8294 31684.2105

Graph 1: Graph of velocity against Reynold’s Number.

DISCUSSION

There are three types of flow in fluid mechanics; laminar flow, transitional flow and

turbulent flow. Basically, this experiment was done to study about the characteristics of the three

basic types of the flow especially the relation between velocity and Reynold’s Number, Re. For

Reynold’s Number value < 2300, the flow is considers as laminar while for Reynold’s Number >

4000, the flow is categorize as turbulent flow. In between 2300 and 4000, the flow considers as

transitional flow which is a combination of transitional and turbulent.[1] Roughly, the procedure

of this experiment is about controlling the outlet control valve in order to manipulate the flow

rate to observe the fluctuation of Reynold’s Number value.

For this Osbourne-Reynold’s Demonstration Experiment, the readings were taken for

four times in order to ensure the accuracy of the result obtained. However, along the experiment,

the same volume of water was used; 4L, which was then converted into m3, given us the value of

0.004m3. For the first one, the time taken was 66s and the high measured was 16cm.Next, the

volume of water was divided with time to obtain the flow rate of the water. The value calculated

was 6.0606 x 10-5 m3/s. Then, to determine the velocity of the fluid flows, the flow rate, 6.0606 x

Reynolds Number

Velocity (m3/s)

10-5 m3/s was divided by the cross sectional area of the pipe, 7.854 x 10-5 m2 which is equal to

0.7717 m/s. Note that the cross sectional area value , A, was constant during this experiment. To

calculate Reynold’s Number, Re, the velocity obtained before was multiply by diameter of the

test pipe, 0.001m (also constant) and divided by kinematic viscosity, ν (0.893 x 10-6 m2/s) of

water at temperature 25KC which was equal to 0.7717 m/s. Note that the same value of kinematic

viscosity, ν was applied in all calculation since the assumption of temperature of water was

constant during the experiment was valid. The Reynold’s Number obtained at the end which is

8641.6573 showed that the flow was turbulent.

For the second one, the time recorded was 35s and the high measured was 16.4cm. The

flow rate calculated which is 1.1429 x 10-4 m3/s then was divided by cross sectional area of the

pipe, gave the value of velocity which equal to 1.4552 m/s. The Reynold’s Number calculated

for second reading was 16295.6327; showed that the flow is turbulent. The next one, the time

recorded was 25s and high measured was 16.7cm. The flow rate, velocity and Reynold’s Number

for this time was 1.6 x 10-4m3/s, 2.0372 m/s and 22812.9899 respectively. Still the result

considered as turbulent. The last reading gave 18 s and 18.3 cm high of the water with flow rate

2.2222 x 10-4m3/s. Then, the velocity calculated by referred to time was 2.8294 m/s and the

Reynold’s Number obtained was 31684.2105. From Reynold’s Number determined, the flow

again was classified as turbulent flow. Note that high of the water was only a reference in order

to manipulate the flow rate. It was not applied in the calculation at all. Interpreted from Table 1,

when the high is increased, the flow rate increased too. On the other hand, the time taken to

collect the water decreased as increasing the velocity of the flow. It can be seen clearly by

comparing the data for 1st and 2nd reading. The first high was small compared to the second one.

Hence the volume flow rate for the first reading was trifled than the second one. However the

velocity was higher and this contributed to the decreased of time taken. Although all the flow

obtained was turbulent, still the pattern of the result can be observed. It can be clearly seen from

the data recorded that the third and forth readings pattern were as same as the previous readings (

1st and 2nd reading ).

Translated the data from Graph 1, it can be concluded that the velocity was directly

proportional to the Reynold’s Number. In other words, when the velocity is increase, the value of

Reynold’s Number will increase too. This explained why the graph obtained was a linear graph.

The one and only observation got from this experiment is about Reynold’s Number since the dye

injection was not provided during the experiment. Supposedly the injection of the dye will show

the velocity profile clearly throughout the flow. However in this case, the velocity profile still

exist but it cannot be observed by naked eyes since the water is colorless and the higher velocity

of the water itself does not permit detail observation on velocity profile. Due to the result, all the

flow were turbulent because it was hard to control the valve in order to lower the level of the

water inlet. Basically, to get laminar and transitional flow, only small turning of the control valve

are required. However some problem occurred during this step. Though the experimenter gave

small turning only on the control valve, still the water enters the column too fast. This explained

why the range of reference high chosen was corresponding to each other. The other reason

caused by the viscosity of the water itself. Viscosity is defined as a measure of the resistance of a

fluid which is being deformed by either shear stress or tensional stress. In everyday terms ,

viscosity can be classified as "thickness" ( valid for fluid only). For example; water is "thin",

having a lower viscosity, while oil is "thick", having a higher viscosity. Generally water can be

classified as fluid that is having low viscosity; means that the resistance in water is lower. Thus,

in water the flow was smooth compared to the one with high viscosity. This explained why the

velocity in the water flow is higher, hence lead it into turbulent group.

CONCLUSION

The study and the experiment done on the Osborne Reynolds Apparatus prove the theory

and show clearly the purpose of the Reynolds Number in laboratory procedures and conditions.

The operation satisfied fully in terms of the results obtained. From the experiment, the results

shows that when the water flow rate are increased, so as the Reynolds number. It clearly verified

the concepts of Reynolds number and the flow of water in the pipe. However, the results from

the calculation shows that all flows obtained are turbulent flow. The types or behavior of the

flow can be determined directly by inspecting the pattern due to the dye injection on the water

flow. This shows that in most of the industries, turbulent flow is mostly used compared to

laminar flow. Turbulent flow is essential in most of chemical processes. Laminar flow occurs

when the Reynolds number calculated is below than 2300. Transitional flow occurs when

Reynolds number calculated is between 2300 and 4000 while turbulent flow occurs when

Reynolds number calculated is above 4000. Lastly, the Reynolds number is also proven that it is

dimensionless. No units left after the calculation.

RECOMMENDATIONS

There are many things on how to improve a system so it works best under certain

conditions. In this case, one of the improvements that can be done is by ensuring that the dye

injection is functioning. It will helps on determining the types and behavior of the flow. Thus,

the results can be seen directly at the moment. Other than that, the experimenter may consider on

running the experiment at non-vibrating place and are free from any disturbance to ensure the

accuracy of the experiment. This will help on determining the exact flow of the water. Other

disturbance such as vibrating condition may cause laminar flow to turn out to be turbulent flow.

Next, the volume flow rate valve should be handled carefully. The valve should be twist slowly

to avoid large difference in water volume flow rate. This is crucial on providing varieties of

results. By handling the valve carefully, it may be possible to obtain laminar flow.

While the experiment is on the run, it is noticed that there are some leakage problems on

the apparatus. This may somehow affect the results obtained. So as to obtained better results with

more accuracy, make sure there is no leakage of the pipe connection. In addition, the

experimenter may prepare the apparatus five minutes earlier before the experiment started

APPENDICES

Figure 1: The schematic diagram for The F1-20 Reynolds’ Apparatus

Figure 2: One of the experimenter control the bench control valve and another take the reading of water level height.

Figure 2: Experimenter taking the initial height of water level.

REFERRENCE

1. F1 Hydraulic Bench. (December 2009). Discover with armfield Engineering Teaching &

Research Equipment. Retrieved February 18, 2010, from

http://www.discoverarmfield.co.uk/data/f1/

2. F1-20 Osborne Reynold’s Demostration. (December 2009).

Discover with armfield Engineering Teaching & Research Equipment. Retrieved

February 18, 2010, from http://www.discoverarmfield.co.uk/data/f1/f1_20.php