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APPRECIATION

Thanks God, we give thanks to the Almighty for His grace and we can set up a report entitled

‘highway laboratary (CC 302)'. Appreciation and gratitude goes to Pn. Hazilah as lecturer

highway engineering for their help, cooperation, guidance, advice and practical ideas that poured

along the run.

Thankfully we have colleagues who help others and help each other work, here are our group

members, Hilmi, Syahiruddin, Zaim, Luqman, Nurul Shafiqa, Noor Syafiqah, Asyikin, and

Amiera are always striving to complete this highway laboratary work.

Moreover, not least thank you to friends, colleagues and all those who have helped us either

directly or indirectly. Hopefully reports this produced a certain extent helped to increase the

effectiveness student learning and enhance students' knowledge in the subjects studied civil

engineering in general and in particular Highway Engineering.

Thank you.

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INTRODUCTION

The purpose of this experiment is to illustrate the influence of Reynolds number on pipe flows.

Reynolds number is a very useful dimensionless quantity (the ratio of dynamic forces to viscous

forces) that aids in classifying certain flows. For incompressible flow in a pipe Reynolds number

based on the pipe diameter, ReD = VaveDρ/μ, serves well. Generally, laminar flows correspond

to ReD < 2100, transitional flows occur in the range 2100 < ReD < 4000, and turbulent flows

exist for ReD > 4000. However, disturbances in the flow from various sources may cause the

flow to deviate from this pattern. This experiment will illustrate laminar, transitional, and

turbulent flows in a pipe.

The apparatus used here to demonstrate ‘critical velocity’ is based on that used by Professor

Reynolds who demonstrated the nature of the two modes of motion flowing in a tube, example

laminar and turbulent. The unit is designed to be mounted on P6100 hydraulic Bench and the

quantity of water flowing through it can be measured and timed using the Hydraulic Bench

Volumetric Tank and a suitable stopwatch. A bell mounted glass tube 790mm long overall by

16mm bore is mounted horizontally and concentrically in a much larger diameter tube fitted with

baffles. A uniform supply of water can then be made to flow along the 16mm bore tube.

The unit is fitted with a constant head tank and the flow rate which can be varied by adjustment

to the head tank height, can be measured using the volumetric tank.

A dye injector is situated at the entrance to the 16 mm bore tube and thus it is possible to detect

whether the flow is streamline or turbulent.

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Critical velocities and Reynolds number

Reynolds obtained the loss of pressure head in a pipe at different flow rates by measuring the

loss head (hf) over a known length of pipe (l), from this slope of the hydraulic gradient (i) was

obtained.

i=hfl

When Reynolds plotted the results of his investigation of how energy head loss varied with the

velocity of flow, he obtained two distinct regions separated by a transition zone. In the laminar

region the energy loss per unit length of pipe is directly proportional to the mean velocity. In the

turbulent flow region the energy loss per unit length of pipe is proportional to the mean velocity

raised to some power, ƞ. The value of ƞ being influenced by the roughness of the pipe wall.

hflα v1.7 For smooth pipes in this region but

hflα v2 for very rough pipes.

Examplehflα v1.7¿2.¿. The dimensionless unit Reynolds number (Re) = ρvd/μ and has a value

below 2000 for laminar flow and above 4000 for turbulent flow (when any consistent set of units

is used) – the transition zone lying in the region of Re 2000 – 4000 (example ‘lower critical

velocity’ LCV at Reynolds number of 2000 and ‘upper critical velocity’ UCV at a Reynolds

number of 4000)

Note that the value of Re obtained in experiments made with ‘increasing’ rates of flow will

depend on the degree of care which has been taken to eliminate disturbance in the supply and

along the pipe. On the other hand, experiment made with ‘decreasing’ flow rates will show a

value of Re which is very much less dependent on initial disturbance.

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OBJECTIVE

The objective of the experiment are :

To observe the characteristics of the flow of a fluid in a pipe, this may be laminar, transitional or turbulent flow by measuring the Reynolds number and the behavior of the flow.

To calculate and identify Reynolds number (Re) for the laminar, transitional and turbulent flow.

To demonstrate the differences between laminar, turbulent, and transitional fluid flow, and the Reynolds’s numbers at which each occurs.

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THEORY

Osborne Reynolds in 1883 conducted a number of experiments to determine the Laws of

Resistance in pipes to classify types of flow. Reynolds number 'Re' is the ratio of inertia force to

the viscous force where viscous force is shear stress multiplied area and inertia force is mass

multiplied acceleration. Reynolds determined that the transition from laminar to turbulent flow

occurs at a definite value of the dimensionally property, called Reynolds number :

Where:

v = flow velocity (m/s)

ρ = density (kg/m³)

d = inside diameter of pipe section (m)

μ = dynamic viscosity of the fluid (kg/ms)

Q = volumetric flow rate (m³/s)

A = cross sectional area of the pipe (m²)

ν = kinematics viscosity (m²/s)

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Reynolds carried out experiments to decide limiting value of Reynold's number to a quantitatively decide whether the flow is laminar or turbulent. The limits are as given below:

Laminar when Re < 2300 Transition when 2300 < Re < 4000 Turbulent when Re > 4000

Figure 2 : Three flow regimes: (a) laminar, (b) transitional & (c) turbulent

The motion is laminar or turbulent according to the value of Re is less than or greater than a certain value. If experiments are made with decreasing rate of flow, the value of Re depends on degree of care which is taken to eliminate the disturbances in the supply or along the pipe. On the others hand, if experiments are made with decreasing flow, transition from turbulent to laminar flow takes place at a value of Re which is very much depends on initial disturbances. The valve of Re is about 2000 for flow through circular pipe and below this the flow is laminar

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in nature. The velocity at which the flow in the pipe changes from one type of motion to the other is known as critical velocity.

APPARATUS

The following apparatus is required.

NO NAMES INSTRUMENT

1) Hydraulic bench

2) Osborne Reynolds Demonstration Apparatus

3) Stop watch

4) Dye

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5) Thermometer

6) Measuring cylinder

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Figure 1: Osborne Reynolds Demonstration Apparatus

1. Base Plate 8. Test Pipe Section

2. Water Reservoir 9. Ball Block

3. Overflow Section 10. Waste Water Discharge

4. Aluminium Well 11. Connections for Water Supply

5. Metering Tap 12. Drain Cock

6. Brass Inflow Tip 13. Control valve

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7. Flow-Optimised Inflow

PROCEDURE

(After choosing a suitable sampling site, follow the procedures below)

1. Firstly, the apparatus is set up and measure and note down diameter of pipe and also

room temperature. Fill the aluminium well with dye, the metering tap (dye flow control

valve) and drain cock must be closed.

2. Switch on the pump, carefully open the control valve above the pump and adjust the tap

to produce a constant water level in the reservoir. After a time the test pipe section is

completely filled.

3. Open the drain cock slightly to produce a low rate of flow into the test pipe section.

4. Open the metering tap and the dye is allowed to flow from the nozzle at the

entrance of the channel until a coloured stream is visible along the test pipe section. The

velocity of water flow should be increased if the dye accumulates around the nozzle.

5. Adjust the water flow until a laminar flow pattern which is a straight thin line or

streamline of dye is able to be seen along the whole test pipe section.

6. Collect the time in seconds for the 10 liters volume of coloured waste water that flows

down at the outlet pipe. The volume flow rate is calculated from the volume and a known

time.

7. Repeat step 5-6 with increasing rate of flow by opening the drain cock and the flow

pattern of the fluid is observed as the flow changes from laminar to transition and

turbulent. Take five to six readings till the dye stream in the test pipe section breaks up

and gets diffused in water.

8. Clean all the apparatus after the experiment is done.

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RESULT

END RESULTS

Inside diameter of pipe section,d = 0.010 m

Cross sectional area of the pipe, A = 7.854x10−3 m²

Density of water, ρ = 1000 kg/m3

Kinematics viscosity of water at room temperature, ν = 0.697 m²/s (see Table 1)

Average room temperature,Ө = 37 ºC

Run No.

Volume, V ( m3)

Time, t (S)

Flow rate, Q(m3/s)

Velocity, v (m/s)

Reynolds Number(RE)

Type of Flow

1 0.01 2.55 4 x 10−3 0.51 7.32 x 10−3 Laminar

2 0.01 2.85 3.51 x 10−3 0.45 6.46 x 10−3 Laminar

3 0.01 3.25 3.125 x 10−3 0.40 5.73 x 10−3 Laminar

4 0.01 3.35 3.030 x 10−3 0.39 5.60 x 10−3 Laminar

5 0.01 3.75 2.703 x 10−3 0.34 4.88 x 10−3 Laminar

6 0.01 3.95 2.564 x 10−3 0.33 4.73 x 10−3 Laminar

Formula :

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CALCULATION

Bell mounted glass tube (length =790 mm, diameter=16mm)

Therefore the area,A = πd²/4 = 2.01×10-4 m²

Reynolds number (dimensionless constant)

Q = ѵs

(m³/s)

Q = volumetric flowrateѴ= volume s= time

V = QA

V=VelocityA=Area of the pipe

Re = ρvdμ

Where,

ρ = density (kg/m³ )

d = diameter (m)

V = velocity (m/s)

µ = viscosity (kg/ms)

Water density,ρ = 1000 kg/m³

Water viscosity, µ = 1.0× 10ˉ³kg/ms

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No. Flow Rate & Velocity Re = v dν

Description

1

V = 0.01m³

Q = 0.01m ³2.55 s

= 4 x 10−3 m³/s

v = 4 x10−3m ³ /s

7.854 x10−3m2

= 0.51 m/s

Re = (0.51)(0.010)

0.697

= 7.32 x 10−3

Laminar

2

V = 0.01m³

Q = 0.01m ³2.85 s

= 3.51 x 10−3 m³/s

v = 3.51x 10−3m ³/s7.854 x10−3m2

= 0.45 m/s

Re = (0.45)(0.010)

0.697

= 6.46 x 10−3

Laminar

3

V = 0.01m³

Q = 0.01m ³3.25 s

= 3.125 x 10−3m³/s

v = 3.125x 10−3m ³/ s

7.854 x10−3m2

= 0.40 m/s

Re = (0.40)(0.010)

0.697

=5.73 x 10−3

Laminar

V = 0.01m³

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4

Q = 0.01m ³3.35 s

= 3.030 x 10−3m³/s

v = 3.030x 10−3m ³/ s

7.854 x10−3m2

= 0.39 m/s

Re = (0.39)(0.010)

0.697

= 5.60 x 10−3

Laminar

5

V = 0.01m³

Q = 0.01m ³3.75 s

= 2.703 x 10−3 m³/s

v = 2.703x 10−3m ³/ s

7.854 x10−3m2

= 0.34 m/s

Re = (0.34 )(0.010)

0.697

= 4.88 x 10−3

Laminar

6

V = 0.01m³

Q = 0.01m ³3.95 s

= 2.564 x 10−3 m³/s

v = 2.564 x10−3m ³ /s

7.854 x 10−3m2

= 0.33 m/s

Re = (0.33)(0.010)

0.697

= 4.73 x 10−3

Laminar

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DISCUSSION

Laminar flow- highly ordered fluid motion with smooth streamlines.

Transition flow -a flow that contains both laminar and turbulent regions.

Turbulent flow -a highly disordered fluid motion characterized by velocity and

fluctuations and eddies.

According to the Reynolds`s experiment, laminar flow will occur when a thin filament of dye

injected into laminar flow appears as a single line. There is no dispersion of dye throughout the

flow, except the slow dispersion due to molecular motion. While for turbulent flow, if a dye

filament injected into a turbulent flow, it disperse quickly throughout the flow field, the lines of

dye breaks into myriad entangled threads of dye.

In this experiment we have to firstly is to observe the characteristic of the flow of the fluid in

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

behaviour of the flow, secondly to calculate the range for the laminar and turbulent flow and

lastly to prove the Reynolds number is dimensionless by using the Reynolds number formula.

After complete preparing and setup the equipment we run this experiment. But firstly we

have to calculate the area of bell mounted glass tube, the viscosity of water and the density of

water. The density of water is 1000 kg/m³, the area of glass tube is 2.01×10-4 m², while the

viscosity of water is 1.0× 10ˉ³kg/ms, this is done for easy step by step calculation.

We observe that the red dye line change with the increasing of water flow rate. The shape

change from thin threads to slightly swirling which still contains smooth thin threads and then

fully swirling. We can say that this change is from laminar flow to transitional flow and then to

turbulent flow and it’s not occurs suddenly.

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CONCLUSION

Finally, As the water flow rate increase, the Reynolds number calculated also increase

and the red dye line change from thin thread to swirling in shape.

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. It is proved that the

Reynolds equation is dimensionless, no units left after the calculation

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RECOMMENDATION

Compare with the result diagram in the laboratory, there are bit different between the

results collected. This might be some of parallax error such as the slow response during

collecting the water, the position of eyes during taking the value of water volume, time taken for the

volume of water and regulating the valve which control the flow rate of water unstably.

During the experiment there are several precaution steps that need to be alert. The

experiment should be done at suitable and unshaken place. To get appropriate laminar smooth

stream flow, the clip and the valve which control the injection of red dye must be regulate slow

and carefully. When removing the beaker from the exit valve, we notice that some water still

enter the beaker because of the slow response between the person who guide the stop watch and

collecting beaker. So to avoid this parallax error, it is better to take same person who guard the stop watch

and the collecting beaker.

Lastly, do this experiment at steady place, control the clip and valve carefully to get long thin of

laminar dye flow, and remove the beaker which uses to collect the amount of water at sharp when the

time is up, to avoid error flow rate error.

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REFERENCES

Internet References

http://en.wikipedia.org/wiki/ReynoldsNumber

Book References

Modul C 3009 ( Hidraulik 1 Jabatan Kejuruteraan Awam Politeknik Kota Kinabalu )

High-Reynolds number Rayleigh-Taylor turbulence Authors: D. Livescu; J. R. Ristorcelli; R. A. Gore; S. H. Deana; W. H. CabotDOI: 10.1080/14685240902870448Published in:  Journal of Turbulence, Volume 10, N 13   2009First Published on: 01 January 2009

Structure of a high-Reynolds-number turbulent wake in supersonic flowJ. P.  Bonnet, V.  Jayaraman and T. Alziary De  Roquefort Laboratoire d'Etudes Aérodynamiques et Thermiques, Laboratoire Associé au C.N.R.S. 191, Centre d'Etudes Aérodynamiques et Thermiques, 43 Route de l'Aérodrome, 86000 Poitiers, France.Journal of Fluid Mechanics (1984), 143:277-304 Cambridge University PressCopyright © 1984 Cambridge University Pressdoi:10.1017/S002211208400135X

Lecturer References

( Pn Hazilah Binti Mohamad, Lecturer of Hydraulics 1 DKA3B )

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