BMM3521

ENGINEERING FLUID MECHANICS LAB

SECTION 03

TITLE: EXPERIMENT 03: DETERMINATION OF FRICTION LOSSES

IN PIPES

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No. Contents Page(s)

1. ABSTRACT 3

2. BRIEF BACKGROUND 4-5

3. OBJECTIVES 6

4. EQUIQMENTS AND MATERIALS 6

5. EXPERIMENT PROCEDURES 7 - 10

6. RESULTS(a) Straight Pipe

-Head Loss-Volume Flow Rate-Velocity-Reynold’s Number, Re-Measured Friction Coefficient-Calculated Friction Coefficient-Calculated Head Loss

(b) Pipe Elbows and Bends

-Head Loss-Volume Flow Rate-Velocity-Minor Loss Coefficient, K-Reynold’s Number, Re-Calculated Friction Coefficient- Measured Friction Coefficient-Calculated Head Loss

Head Loss vs. Velocity GraphPipe Coefficient of Friction vs. Reynolds Number Graph1SAMPLE CALCULATIONS

11 - 15

7. QUESTIONS 16 - 17

8. DISCUSSIONS 17

9. CONCLUSION 17

10. REFERENCES 17

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ABSTRACT

This report was written in order to fullfill the requirement of subject of Engineering Fluids Mechanics Laboratory (BMM 3521). As this is the third experiment that conducted by us, the title of the experiment is Determination of friction losses on pipes. Closed circuit of any cross-section used for flow of liquid is known as apipe. In hydraulics, generally, pipes are assumed to be running full and ofcircular cross section. Liquids flowing through pipes are encountered withfrictional resistance resulting in loss of head or energy of liquids.

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BRIEF BACKGROUND

Pipe flow under pressure is used for a lot of purpose. A fundamental understanding of fluid flow is essential to almost every industry related with chemical engineering. In the chemical and manufacturing industries, large flow networks are necessary to achieve continuous tranport of products and raw materials from different processing units. This requires a detailed understanding of fluid flow in pipes. Energy input to the gas or liquid is needed to make it flow through the pipe. This energy input is needed because there is frictional to energy loss (also called frictional head loss or frictional pressure drop) due to the friction between the fluid and the pipe wall and internal friction within the fluid. In pipe flow substantial energy is lost due to frictional resistances.

One of the most common problems in fluid mechanics is the estimation of this pressure loss. Calculating pressure losses is necessary for determining the appropriate size pump. Knowledge of the magnitude of frictional losses is of great importance because it determines the power requirements of the pump forcing the fluid through the pipe. For example, in refining and petrochemical industries, these losses have to be calculated accurately to determine where booster pumps have to be placed when pumping crude oil or other fluid in pipes to distances thousands of kilometres away.

Pipe losses in a piping system result from a number of system characteristics, which include among others; pipe friction, changes in direction of flow, obstruction on flow path, and sudden or gradual changes in the cross-section and shape of flow path.

Resistance to flow in a pipe

When a fluid flows through a pipe, the internal roughness of the pipe wall can create local eddy currents within the fluid adding a resistance to flow of the fluid. The velocity profile in a pipe will show that the fluid elements in the center of the pipe will move at a higher speed than those closer to the wall. Therefore friction will occur between layers within the fluid. This movement of fluid elements relative to each other is associated with pressure drop, called frictional losses. Pipes with smooth walls such as glass, copper, brass and polyethylene have only a small effect on the frictional resistance. Pipes with less smooth walls such as

concrete, cast iron and steel will create larger eddy currents which will sometimes have a significant effect on the frictional resistance. Rougher the inner wall of the pipe, more will be the pressure loss due to friction.

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As the average velocity increases, pressure losses increase. Velocity is directly related to flow rate.

Velocity=Volumetric flow rate /Cross sectional area of the pipe

An increase or decrease in flow rate will result in a corresponding increase or

decrease in velocity. Smaller pipe causes a greater proportion of the liquid to be in contact with the pipe, which creates friction. Pipe size also affects velocity. Given a constant flow rate, decreasing pipe size increases the velocity, which increases friction. The friction losses are cumulative as the fluid travels through the length of pipe. The greater the distance, the greater the friction losses will be. Fluids with a high viscosity will flow more slowly and will generally not support eddy currents and therefore the internal roughness of the pipe will have no effect on the frictional resistance. This condition is known as laminar flow.

The Reynolds number expresses the ratio of inertial (resistant to change or motion) forces to viscous forces.

Where D is the diameter of the pipe

ρis the density of fluid

V is the average velocity of the fluid

µ is the viscosity of fluid.

The Reynolds number can be written in terms of kinematic viscosity

The Reynolds number is important in analyzing any type of flow when there is

substantial velocity gradient (i.e. shear.) It indicates the relative significance of the

viscous effect compared to the inertia effect.

The flow is

• laminar when Nre < 2100

• transient when 2100 < Nre < 4000

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• turbulent when 4000 < Nre

OBJECTIVE

1) To design complete measurement technique for fluid flow and determine major and minor losses in different piping system.

2) To investigate the velocity for different diameters of pipe.

EQUIQMENTS AND MATERIALS

a) Pipe friction apparatus b) Sensorsc) Personal Computer with DasyLabd) Data Acquisition Systeme) National Instrument Equipment (NI)

Pipe friction apparatus.

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PROCEDURE

a) Straight Pipe

1. The pipe friction apparatus were checked to make sure the apparatus were in a good condition so that any error in the result can be minimize.

2. The strain gauge sensors connected to the National Instrument (NI9219) were fitted to the pipe.

3. The flow sensor were connected to the National Instrument (NI9201).

4. The National Instrument were make sure that it is connected to the computer with DasyLab setup.

5. The voltage generated by the flow sensor were converted into frequency using DasyLab.

6. The volume flow rate were determined manually by measuring the time taken of water to fill up 5 Litres. The step were repeated 5 times using different speed of the water flow.

7. The graph of volume flow rate versus frequency was plotted in Microsoft Excel in order to obtain synchronized values of a and b for the DasyLab setup.

8. The strain gauge sensors were calibrated with value a and b that were written in it.

9. The scaling process were done in the DasyLab before the pipe friction apparatus were operated to reduce any error in the digital meter reading.

10. Again, the scaling process were done after the pipe friction apparatus were operated to eliminate any error in the DasyLab digital meter reading.

11. The pressure differences between the inlet and outlet pipe were obtained using DasyLab digital meter.

12. The velocity, measured and calculated head loss, measured and calculated pipe coefficient of friction and Reynolds number were obtain using the Formula Interpreter in the DasyLab.

13. The result were recorded and tabulated.

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b) Pipe Elbow, 450 Pipe and Pipe Bends

1. Step 1 to 10 in the straight pipe friction experiment were repeated for this experiment.

2. The pressure differences between the inlet and outlet of pipe elbow, 45o pipe and pipe bends were obtained using DasyLab digital meter.

3. The velocity, measured and calculated head loss, measured and calculated pipe coefficient of friction ,Reynolds number and minor loss friction were obtain using the Formula Interpreter in the DasyLab for pipe elbow, 45o pipe and pipe bend.

4. The result were recorded and tabulated.

Procedure of Setup Virtual Instrument Software

Click open the NI-DAQ system software and click data neighborhood and create new task. Then Analog Input were selected according the sensors that we were using (strain).

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The channels a2 and a3 which is connected to the National Instrument were selected.

Then, the value of gauge factor and gage resistance which is 2.11 and 119.5 respectively were inserted. Then, the Quarter Bridge 1 were selected at strain configurations.

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The voltage input were added for flow sensor. Then, the button Run were clicked and the data were saved.

The DasyLab were set up as shown in the figure. Input 0 is for the flow rate measurement, Input 1 is for the pressure head 1(head loss 1) measurement and Input 2 is for the pressure 2 measurement (head loss 2).After the setup were finished, the measurement button were clicked and hardware setup were selected, then NI-DAQmx selected and finally synchronise with max configuration.Finally, the setup were run and the data were collected.

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RESULTS

Straight Pipe

Length of pipe, l=800mm

PVC pipe internal diameter = 20 mm

PVC pipe outside diameter = 23 mm

Volume Flow rate, m3/s

Head loss, m

Measured friction coefficient

Velocitym/s

Reynolds number, Re

Calculated coefficient of friction

Calculated head loss, m

0.091 0.0758 0.6154 0.2577 4891 0.0491 0.00710.124 0.0785 0.2451 0.3258 5146 0.0375 0.01180.137 0.0794 0.2035 0.4362 5741 0.0320 0.01270.151 0.0795 0.1872 0.4583 8983 0.0307 0.01340.168 0.0809 0.1371 0.5474 10732 0.0301 0.01700.198 0.0821 0.0998 0.6335 12644 0.0296 0.0240

Elbow Pipe

Length of elbow pipe = 203 mm

Volume Flow rate, m3/s

Head loss, m

Measured friction coefficient

Velocitym/s

Reynolds number, Re

Calculated coefficient of friction

Calculated head loss, m

0.211 0.0861 0.0425 0.6321 5452 0.0243 0.00670.226 0.0869 0.0463 0.6642 6243 0.0367 0.00700.248 0.0884 0.0486 0.6859 6651 0.0451 0.00730.317 0.0925 0.0531 0.7238 7845 0.0498 0.00850.329 0.0946 0.0564 0.7580 8079 0.0544 0.00940.344 0.0961 0.0592 0.7981 8570 0.0646 0.0116

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Bend Pipe

Lengths of bend pipe = 322 mm

Volume Flow rate, m3/s

Head loss, m

Measured friction coefficient

Velocitym/s

Reynolds number, Re

Calculated coefficient of friction

Calculated head loss, m

0.211 0.0724 0.3402 0.6321 5452 0.0243 0.01250.226 0.0735 0.3631 0.6642 6243 0.0367 0.01480.248 0.0752 0.3750 0.6859 6651 0.0451 0.01690.317 0.0769 0.3921 0.7238 7845 0.0498 0.02310.329 0.0778 0.4210 0.7580 8079 0.0544 0.02660.344 0.0783 0.4355 0.7981 8570 0.0646 0.0283

45 o Angle Pipe

Length of angle 45° pipe = 247 mm

Volume Flow rate, m3/s

Head loss, m

Measured friction coefficient

Velocitym/s

Reynolds number, Re

Calculated coefficient of friction

Calculated head loss, m

0.211 0.0710 0.3321 0.6321 5452 0.0243 0.00780.226 0.0728 0.3365 0.6642 6243 0.0367 0.01260.248 0.0745 0.3410 0.6859 6651 0.0451 0.01440.317 0.0760 0.3448 0.7238 7845 0.0498 0.01680.329 0.0774 0.3660 0.7580 8079 0.0544 0.01880.344 0.0781 0.3821 0.7981 8570 0.0646 0.0216

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Head Loss vs. Velocity Graph

0.2577 0.3258 0.4362 0.4583 0.5474 0.63350

0.02

0.04

0.06

0.08

0.1

0.12

Head loss vs Velocity

Calculated Head LossMeasured Head Loss

Head

Loss

Pipe Coefficient of Friction vs. Reynolds Number Graph

4891 5146 5741 8983 10732 126440

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Pipe coefficient of friction vs. Reynolds Numbers

Measured coefficientCalculated Coefficient

Pipe

Coe

fficie

nt

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Total loss ; H Loss=∑Hmajor losses

Total Loss = (0.0785+0.0790+0.0779+0.0786+0.0804+0.0817)

= 0.4761m

SAMPLE CALCULATIONS

These are the sample calculations for our result obtained shown in result part.

Straight Pipe

Volume Flow Rate, Q=Volumeof watertime

=5×0.001

61.31

=0.000092 m3/s

Flow Speed, V= 4Q

π d2

=4(0.000082)/π(20x10-3)2

=0.2579 m/s

Assuming that the water is at room temperature, Troom=20。C

Density of water, p=1000kg/m3

Dynamics Viscosity, µ= 1.002×10-3

Reynolds Number, Re= ρ vd

μ

= (1000) (0.2578) (20x10-3)/ 1.002×10-3

=4920

For Calculated, using Colebrook Equation, f=0.25¿¿¿

Roughness of pipe PVC,ɛ=0mm (smooth)

= 0.25/(log (5.74/(49200.9)2)

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=0.0420

For Measured, f=2hdg

l v2

=2(0.0476) (20 x10-3) (9.81)/ (0.8) (0.25782)

=0.5794

Head Loss for calculation, hloss=fl v2

2dg

= (0.0375) (0.8) (0.25782) / 2 (0.02)(9.81)

= 0.0051m

Measured Head loss = h1- h2

= 0.2938-0.2153= 0.0785m

Pipe Elbow 45 0 Pipe and Pipe Bends

Volume Flow Rate, Q=0.211 ×10-3

Flow Speed, V= 4Q

π d2

= 4(0.211 ×10-3 )/π(0.022)

= 0.672m/s

Assuming that the water is at room temperature, Troom=20。C

Density of water, p=1000kg/m3

Dynamics Viscosity, µ= 1.002 x10-3

Reynolds Number, Re= ρ vd

μ

= (1000) (0.672) (0.02)/ 1.002 x10-3

= 5440

Pipe Coefficient of Friction

Using Colebrook Equation, f=0.25¿¿¿

Roughness of pipe PVC, ɛ=0mm (smooth)

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= 0.25/(log (5.74/(54400.9)2)

=0.0340

For Measured, f=2hdg

l v2

=2(0.0866) (20 x10-3) (9.81)/ (0.8) (0.6722)

=0.094

Minor Loss Coefficient, K= 2ghloss / v2

= 2 (9.81) (0.0068) / 0.6722 = 0.2954

QUESTION:

Explain how the strain gauge senses the pressure?

Strain gauges are sensing devices used in a variety of physical test and measurement applications. They change resistance at their output terminals when stretched or compressed. Because of this characteristic, the gauges are typically bonded to the surface of a solid material and measure its minute dimensional changes when put in compression or tension. In this experiment, the strain gauge convert the pressure detected by water inside the tube into resistance. The value of resistance will produce potential different (voltage) with this DAQ able to show this information in our computer and results obtained.

How can you connect the measuring devices to the DAQ?

We using an electrical wire to connect measuring devices with DAQ.

What would happen to the head loss if the diameter of the pipe is decreased?

Based on the formula, the head loss is inversely proportional to the diameter, h_L∝1/D

h_L=(fLV^2)/2Dg

If the inside diameter of the pipe is reduced, the flow area decreases, the velocity of the liquid increases and the head loss due to friction increases. Hence, it can be conclude that when the diameter of the pipe is decreased, the head loss will increase.

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What would happen to the head loss if the length of the pipe is decreased?

Based on the formula, the head loss is directly proportional to the length, h_L∝L

h_L=(fLV^2)/2Dg

Head loss due to friction occurs all along a pipe. It will be constant for each foot of pipe at a given flow rate. The published tables have head loss values which must be multiplied by the total length of pipe. Hence, it can be conclude that when the length of the pipe is decreased, the head loss will also decreased.

What are the two types of energy losses typically associated with pipe flow? What determines which one will predominate as the most significant loss of head incurred by a fluid flowing along a pipe?

The 2 types of energy head losses that associated with piping flow is minor head losses and major head losses. If the length of pipe is long, the major head losses will predominates whereas if the pipe shorter and have lots of turning, minor head loss will be predominates.

How can you find the values of minor loss coefficients from your experiment?

Based on the following formula, we able to find the coefficient of minor loss,

K_L=(h_L 2g)/V^2

From experiment we obtained, the h_L is the head loss in the piping system, g is 9.81 which is constant and V is average velocity.

Compare your critical Reynold’s number with the theoretical value at which the transition from laminar to turbulent flow occurs. What are the most significant reasons for the different between the two?

Theoretically, critical Reynold’s number is 2300. The Re number greater than 4000 consider as turbulent flow. As all the result getting from our experiment is exceed 4000 Re number. Hence, the water flow inside the pipe in our experiment is turbulent flow. The difference of laminar flow is low velocity and highly orderly in motion. Turbulent flow is high velocity flow, and it is highly disordered in motion.

DISCUSSION:

Through this experiment we able to conduct experiment with the help of measurement instrument. By using Dasylab, we can collect the data such as flow rate, frequency, velocity,

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pressure and etc. The major and minor head loss of piping system are able to calculate. But the data displayed by DasyLab is not 100% accurate, because the data collected does not include factor and error on our sensor and our system. In order to maximize our data accuracy, we have to follow some precaution step during experiment.

CONCLUSION:

Based on the study, we are gain knowledge on how to explain the design of the piping system that influences the result of the lab which affect the flow rate of the water through the pipe. From our experiment result, we are able to explain the mechanics of fluid friction phenomenon in pipes. Besides that, we able to learn how to use measurement instrument such as Dasylab. With the data or electrical signal senses by strain gauges and flow sensor are analysed and determined by using virtual instrumental software (DASYLab).All the parameters formula key in into Dasylab software to generate all the data base. The parameters are head loss, pipe friction coefficient, loss coefficient, Reynolds number and etc. Therefore at the end of experiment, we can be minimized by proper selection of pipe sizes and fittings that make up a system by using sensors and computer in future work.

REFERENCES:

http://www.sensorland.com/HowPage002a.html

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

http://www.ni.com/getting-started/set-up-hardware/data-acquisition/current

http://www.engineeringtoolbox.com/total-pressure-loss-ducts-pipes-d_625.html

2nd edition of Fluids mechanics fundamental and application, Yunus A. Cengala and John M. Cimbala,2008.

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