EXPERIMENT 3:

REYNOLDS NUMBERS

INTRODUCTION

Reynolds Test is a test by analysis a flow in pipe. When a liquid is flowed in a pipe, it will

appear three type of flow. There are Laminar Flow, Transitional Flow and Turbulent Flow. The

type of the flow can be classify by refer to the type of line of that appear and by calculate the

Reynolds No.

OBJECTIVES

The objectives of the experiment are:

1. To arrange work procedure accordingly

2. To execute safety and health procedure

3. To handle the given task correctly

4. To identify the data needed

5. To accomplish the task within a time frame given

6. To document the task and produce the report

LEARNING OUTCOMES

Upon completion of this course, student should be able to:

1. Apply principles to solve problems in laminar and turbulent flow and relation to

Reynolds number, Darcy’s and Hagen-Poiseuille equation for problem solving.

2. Apply correct methods and procedures of hydraulics solution towards practical problems.

THEORY/BACKGROUND

Fluid flow can be classified to three regimes which is laminar, transitional and turbulent regime.

Laminar regime is a regime where the flow is characterized by smooth streamlines and highly

ordered motion. Turbulent is a regime where flow is characterized by velocity fluctuations and

highly disordered motion. Transitional regime is where the flow fluctuates between laminar and

turbulent before it becomes fully turbulent.

The transitional from laminar to turbulent flow depends on geometry, surface roughness, flow

velocity, surface temperature, and type of fluid. However, Osborne Reynolds discovered that the

flow regime mainly depends on the ratio of inertial forces to viscous forces. This ratio is what

we called as Reynolds number.

At small or moderate Reynolds numbers the viscous forces are large enough to suppress theses

fluctuations and to keep the fluid “in line”. Thus, the flow is streamlined and in ordered motion.

However, at large Reynolds numbers, the inertial forces, which are proportional to the fluid

density and the square of the fluid velocity, are large relative to the viscous force. As the results,

the viscous force cannot prevent the random and rapid fluctuations of the fluid. Thus, the flow

will be in disordered motion.

The boundary of Reynolds number for laminar, transitional and turbulent regime varies by

geometries and flow condition. For example, flow in a circular pipe is laminar for Reynolds

number less than 2300, turbulent for Reynolds number larger than 4000 and transitional in

between. However, we will have other boundaries if the pipe cross sectional area is a square.

This experiment is to visualize the laminar, transitional and turbulent flow in a pipe and to

determine the boundary of Reynolds number for flow in the pipe.

First by controlling the flow rate, establish the laminar flow. Then by slowly increase the flow

rate observes what happened to the dye streak. Record the flow pattern change and its

volumetric flow rate reading. Determine the boundary of Reynolds number for laminar,

transitional and turbulent regime.

Aluminium well

Metering tapBrass inflow tipFlow-optimised inflowGlass ball

Test pipe section

Drain cock

Base plate

Waste water discharge

Connections for water supply

Overflow section

Water reservoir

PROCEDURE

1. Dye filled into the container in the apparatus. Dye liquid valve is closed.

2. Water is supplied to the apparatus tank. The valve controls the flow through a transparent

pipe is closed.

3. Flow control valve is opened slightly. The constant column is obtained.

4. The valve is opened and the flow of dye is controlled so that the colors appear as straight lines.

5. Flow rates is measured.

6. Velocity increased slightly until the dye began to appear wavy-square. This flow rates is

measured.

7. Flow velocity increased again until the dye began to appear dispersed in water and flow is

measured.

8. Dye is poured back into the bottle and the former dye, and the needle is washed after

completion. Water tanks emptied.

EQUIPMENT:

Reynolds Experiment Apparatus

OBSERVATIONS

(i)

Pipe diameter , d 0.01 M

Cross section area, A 7.854 x 10-5 m2

Kinematic viscosity, υ 1 x 10-6 m2/s

(ii)

Volume, V

(m3)

Time, T

(s)

Flow rate, Q

(m3/s)Velocity (m/s)

Sketch of the

dyeFlow type

Reynolds

No.

(Re)

0.004 69.68 5.741 x 10-5 7.310 x 10-11 Laminar 731

0.004 20.53 1.948 x 10-4 2.480 x 10-10 Transition 2480

0.004 7.06 5.666 x 10-4 7.214 x 10-10 Turbulent 7214

DISCUSSION

By referring to the result and calculation, we found that the test to determine Laminar flows was

successful. Reynolds No that we get from the test is 731 that less than 2000 (Re<2000) follow

the character of Laminar flows. The coloring condition of the flow from the test had show a

straight line.

From the test, we was successfully determine the transitional flows with 2480 of Reynolds No

that more than 2000 but less than 4500 (2000<Re >4500). The coloring condition of the flow

from the test had show a straight line and roll line.

The test that we have done to determine turbulent flow was successful. From the calculation, we

get 7214 the Reynolds No that more than 4500 (Re>4500). The coloring condition of the flow

from the test had show a roll line.

CONCLUSION

As a conclusion from the test, we were able to determine type of flows. We successful to identify

the type of flows by calculate the Reynolds No from the result and we also can defined the flow

by line appear.

PRE-LAB QUESTIONS

1. What is Reynolds Number?2. Explain what is the meaning is if one say ‘The flow has low Reynolds Number’?3. Draw velocity profile for fully developed turbulent flow.