EM201 FLUID MECHANICS
LABORATORY REPORT
EXPERIMENT 2
HEAD LOSS IN PIPE & BENDS
Name: GAN KIN LEONG ID: 1001232660 Course: BEng. Petroleum Engineering
FACULTY OF ENGINEERING FACULTY OF ENGINEERING, ARCHITECTURE AND BUILT ENVIRONMENT
SEPT 24, 2013 TABLE OF CONTENT
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CONTENTS
PAGE NO.
1. Introduction a. Objective
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b. Learning Outcomes
3
c. Introduction
3-6
2. Material and Methodology a. Apparatus
6
b. Precautions
7
c. Procedure (Part 1 & 2)
7-8 & 14
3. Results and Discussions a. Results & Calculations (Part 1 & 2) b. Discussions (Part 1 & 2)
8-12 & 14-17 13 & 18
4. Conclusion
18
5. Reference
19
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OBJECTIVE 1. To determine the head loss in pipe flow for different pipe diameter. 2. To estimate the friction factor for different pipe diameter. 3. To determine the head losses in bends. 4. To identify the types of flow of the fluid. LEARNING OUTCOME Upon completion of the experiment, students should be able to determine the head loss in pipe flow for different pipe diameter. In addition, students are able to plot the graph of friction factor against Reynolds number. Students should also be able to determine the head losses in each bend and find the pressure drop along the pipe. Furthermore, they should be able to plot the graph of ΔH against V2/2g to obtain K for all the four bends.
INTRODUCTION If you want to move something, there will be resistance. If you try to push a heavy box along the ground, it will require a certain amount of effort to do it. Since the weight and the size of the box will not change, the work required should be the same regardless of the surface it is resting on. However, the box will be much easier to move on a smooth linoleum floor than trying to move it on a deep pile carpet. The difference in the required effort is due to friction. The carpet has a higher resistance to the movement of the box than the smooth floor. To move a given volume of liquid through a pipe requires a certain amount of energy. An energy or pressure difference must exist to cause the liquid to move. A portion of that energy is lost to the resistance to flow. This resistance to flow is called head loss due to friction.
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In fluid dynamics, head is a concept that relates the energy in an incompressible fluid to the height of an equivalent static column of that fluid. From Bernoulli's Principle, the total energy at a given point in a fluid is the energy associated with the movement of the fluid, plus energy from pressure in the fluid, plus energy from the height of the fluid relative to an arbitrary datum. Head is expressed in units of height such as meters or feet. Head loss is the measure of the reduction in the total head of the liquid as it moves through a system. The total head is the sum of the elevation head, velocity head and pressure head. Head loss is unavoidable and is present because of the friction between the fluid and the walls of the pipe and is also present between adjacent fluid particles as they flow along the pipe. Head loss is a measure of the reduction in the total head (sum of elevation head, velocity head and pressure head) of the fluid as it moves through a fluid system. This is unavoidable in real fluids.
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Head loss is the combination of different types of losses. 1- Friction loss occurs as the fluid flows through the straight pipes. 2- Minor losses are head losses that occur due to bends, elbows, joints, valves, and other fittings in the systems. Whenever there is a change in the direction of flow or a change in the cross-sectional area a head loss will occur. Friction losses are very dependent upon the viscosity of the liquid and the amount of turbulence in the flow. Head loss due to friction can be calculated by using the Darcy-Weisbach equation. Darcy's equation can be used to calculate frictional losses. A special form of this equation can be used to calculate minor losses. Friction loss is that part of the total head loss that occurs as the fluid flows through straight pipes. The head loss for fluid flow is directly proportional to the length of pipe, the square of the fluid velocity, and a term for fluid friction called the friction factor. The head loss is inversely proportional to the diameter of the pipe. When calculating heat transfer or pressure and head loss it is important to know if the fluid flow is laminar, transitional or turbulent. There are in general, three types of fluid flow in pipes
laminar
turbulent
transient
Laminar flow Laminar flow generally happens when dealing with small pipes and low flow velocities. Laminar flow can be regarded as a series of liquid cylinders in the pipe, where the innermost parts flow the fastest, and the cylinder touching the pipe isn't moving at all.
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Transitional flow Transitional flow is a mixture of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the edges. Each of these flows behave in different manners in terms of their frictional energy loss while flowing, and have different equations that predict their behavior. Turbulent flow In turbulent flow vortices, eddies and wakes make the flow unpredictable. Turbulent flow happens in general at high flow rates and with larger pipes. Turbulent or laminar flow is determined by the dimensionless Reynolds Number.
Reynolds Number 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 Reynolds number is proportional to inertial force divided by viscous force. The flow is:
laminar when Re < 2300
transitional when 2300 < Re < 4000
turbulent when 4000 < Re
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APPARATUS Pipe Friction Apparatus, The Hydraulics Bench, its various accessories and the associated experimental equipment as well as a stopwatch.
PRECAUTIONS 1. The manometer tube is ensured to be free from air bubbles and that readings are taken after the water level has been stabilized. 2. The units of the values taken should be converted from millimeters (mm) to meters (m) for standardized calculation. 3. The eye level when recording data should be parallel to the measurements. This is to prevent parallax error. PART 1: HEAD LOSS IN PIPES OF DIFFERENT DIAMETER PROCEDURE (Part 1)
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1. The LS-18001-15 Pipe Friction Apparatus was placed on the hydraulic bench.
2. The water inlet and outlet nipples are connected with flexible hose. 3. The quick coupling is connected to the copper wire of 11mm inner diameter. 4. The water pump is switched on and the hydraulic bench is closed over flow slowly. 5. The valves at the copper pipe are opened and the air gap in the manometer are removed by pressing the relief valve, which is located at the top of the manometer. The flow rate is measured by a measuring beaker and a stopwatch. 6. The reading at the manometer is recorded. 7. Steps 4-6 are repeated with different flow rate and the reading of the manometer is taken. 8. Steps 3-7 are repeated for one other different diameter pipe of my choice. 8
9. A graph of friction factor against Reynolds number is plotted. RESULTS & CALCULATIONS (Part 1) Flowrate=
e.g, :
e.g, :
5 =0.2998 L /s 16.67
Velocity=
flowrate area
0.2998 D2 pi x 4
= 3.155 m/s
ℜ=
e.g, :
volume time
( velocity x diameter ) viscosity
3.155 x 0.011 9.04 x 10−7
= 38390
Friction factor =
e.g, :
(
h L v2 x d 2g
( )( )
0.037 0.425 3.1552 x( ) 0.011 19.62
)
= 1.888
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i) 11 mm
ii) 8.3 mm
iii) 5.3 mm
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DISCUSSIONS (Part 1) According to the results obtained, it can be said that the head loss gets larger when the crosssectional area of the pipe decreases. The 5.3mm pipe showed the largest head loss value. From the calculations, the velocity and Reynolds number for 11mm pipe is the lowest among all the three (3) different sizes of the pipes showing values of less than 40000, which are shown in the graph of friction factor against Reynolds number as plotted above. Therefore, with less than 2400 of Reynolds number, the fluid flowing through the 11mm pipe would be laminar flow where the fluid will move in a straight path. Whereas for the 8.3mm pipe, the Reynolds number is in between laminar flow and turbulent flow with 2600 and 4000, which is transitional flow. In this flow, the fluid will flow in a medium velocity. As for the 5.3mm pipe, with the highest Reynolds number calculated of more than 4000, the fluid will flow in a turbulent flow with high velocity. From the graph, it can deduced that the friction factor is high when the total head loss is high and low when the total head loss is low.
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PART 2: HEAD LOSS IN A BEND PROCEDURE (Part 2) 1. The inlet valve is connected to the hydraulic bench supply. 2. The inlet and outlet valve are fully opened and water flow rate is controlled from the hydraulic bench. 3. The flow rate of water is measured by a measuring beaker and a stopwatch. The water flow rate is set to a suitable value. 4. After the flow rate is steady, if the water level in the manometer tubes is too low, the air relief valve, which is located at the top of the manometer, is pressed. 5. The water level of every tube in the manometer is recorded. 6. Steps 4-5 are repeated for different flow rates. 7. A graph of ΔH against V2/2g to obtain K for all the four bends is plotted.
RESULTS & CALCULATIONS (Part 2) Taking the first reading as an example: volumetric flowrate=
water collected time
volumetric flowrate=
5 =0.2053 L/s 24.35
velocity=
velocity=
volumetric flowrate x 0.001 area 0.2053 X 0.001=0.937 m/s π D2 4
reynolds number=
velocity x diameter viscosity
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reynolds number=
0.937 x 0.0167 =17310 −7 9.04 x 10
friction factor=−0.0016 ln ( x )+ 0.0028 friction factor=−0.0016 ln ( 17310 ) +0.0028=7.19 x 10−3
loss coefficient , K=
loss coefficient , K=
∆h v2 2g 0.0386 =0.86 0.9372 2 ( 9.81 )
For flow rate of 0.2053 L/s
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For flow rate of 0.2053 L/s
For flow rate of 0.1738 L/s
For flow rate of 0.1047 L/s
For flow rate of 0.0699 L/s
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DISCUSSIONS (Part 2) From the results obtained, it can be shown that values of the reading from tube 1 to tube 10 decreases. The readings recorded on the manometer decrease as the flow rate and velocity are lowered. As shown in the manometer, tubes 1 & 2, 3 & 4 and 7 & 8 as well as 9 & 10 are used to measure the head losses for the pipes with 90 degrees large radius bend, 90 degrees small radius bend, 90 degrees small elbow bend and two (2) 45 degrees bends respectively while readings from tubes 5 & 6 are used to measure the sudden contraction and enlargement in large diameters. Based on the calculations in Part 2, the total head loss is highest with the volumetric flow rate. Analyzing the graph plotted, we can see that the head loss in 45 degrees bend is higher than the 90 degrees bend, whereas the head loss in sudden contraction in the pipe diameter is higher than for sudden enlargement in pipe.
CONCLUSION The objectives of the experiment have been achieved. In conclusion for Part 1, the experiment allowed us to determine the head losses in the different cros-sectional areas of the pipes. By calculating the Reynolds number and plotting the values with friction factor, we were able to identify the types of flow of the fluid whether the fluid is laminar flow, transitional flow or turbulent flow.
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In conclusion for Part 2, the experiment allowed us to identify the head losses in different types of pipe bends and the pressure drop along the pipes ranging from different angles of bending and sudden contraction and enlargement. Calculating the results recorded to obtain value of total head losses, the values are plotted in a graph to obtain loss coefficient, K.
REFERENCES 1. Merie Potter (2007). Schaum’s Outline of Fluid Mechanics. McGraw-Hill 2. http://www.engineeringtoolbox.com/reynolds-number-d_237.html 3. http://www.hydromatic.com/ResidentialPage_techinfopage_headloss.aspx
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