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SERIES PIPELINE SYSTEMS Now we bring together all the losses we
have studied to investigate the total loss for a pipe network
Series pipeline fluid flows in a single flowpath through the system
What were the various losses we discussed???
- Friction loss in pipes (major)
hL = f * (L/D) * v2/2g
- losses due to bends, fittings, valves, etc (minor losses)
)2/( 2 gvKhL = We will be studying 3 types of series pipe
systems CLASS I:
Given pipe size, flow rates Determine pressure at some point,
total head from a
pump
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CLASS II:
Given pipe sizes, valves, fittings etc. Given allowable
pressures or pressure drops Determine the allowable flow rate Q in
the system
CLASS III:
Given pipe layout and flow rates Determine pipe sizes
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CLASS I Computations Apply General Energy Equation
hL = sum of
- entrance loss - friction loss in suction line - loss in valve
- loss in elbows - friction loss in discharge line - exit loss
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Example Problem 11.1
Determine Power supplied to pump If
Efficiency = 76% Fluid = methyl alcohol at 25C Q = 54 m3/hr
Suction line 4 steel pipe 15 m long Discharge line 2 steel pipe 200
m long Valve globe valve Entrance from 1 square edged inlet
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NOTE see appendices F-G in TEXT for areas and inside diameters
for steel pipes.
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Correction 789! (table appendix B)
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Table 10.5
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Table 10.4
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ASSIGNMENT # 7: CLASS 1 PIPE SYSTEMS
11.1M 11.2M
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***Some Design Considerations for Series Pipelines:
Keep pressure at inlet to the pump as high as practical but
checks should be made to ensure that cavitation does not occur in
the suction line.
Minimize energy losses in the pipelines. Large diameter
pipes should be selected for long pipe line lengths so as to
reduce friction losses. However the pipe dia should not be
excessively large increases costs.
Length of suction lines should be as short as practical.
ON or OFF valves should be preferred, such as GATE or
BUTTERFLY valves. Where flow needs to be gradually reduced,
GLOBE valves should be used.
Often preferable to put valves on either side of the pump.
Design Changes to CLASS I Problem to reduce losses:
Length of suction line = 15m, appear excessively long, shorten
if possible.
Provide a GATE valve in the suction line
Energy loss in 200m discharge line too high = 185.9 m
(friction); associated with high velocity = 6.92 m/s.
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Recommended range of velocities Suction lines = 0.6 to 1.2 m/s
Discharge lines = 2-5.5 m/s To reduce the velocity in the discharge
line increase the diameter of the pipe. Currently you have 2 inch
pipe. Refer to Figure 6.2 (next page) says to use ~ 21/2 inches;
Adopt 3-inch Velocity head due to 2-inch = 2.44 m Velocity head due
to 3-inch = 0.504 m
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A reduction in energy losses of about 5 times!!
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Currently you have Globe valve in discharge line which has an
equivalent-length ratio = 340. The same value for a fully-open GATE
valve is = 8. A reduction of about 42 times in the energy loss.
Final Summary of proposed design changes
Decrease suction line length from 15 to 1.5 m. Add that length
to discharge line.
Add fully open gate valve in suction line.
Increase discharge line dia from 2 to 3.
Replace globe valve in discharge line with gate valve.
All these changes will lead to reduction in energy added by pump
from 217 m to 37.9 m. the power supplied to the pump would decrease
from 33.2 kW to 5.8 kW a reduction by a factor of 6!!! Cost
analysis should also be done. CLASS II:
Given pipe sizes, valves, fittings etc.
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Given allowable pressures or pressure drops Determine the
allowable flow rate Q in the system
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274.5)/(7.3
1log 9.0
25.0
+
=RND
f
- (Swamee & Jain eqn)
Note Correction D/ = 8889 in eq above!
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CLASS III: Given pipe layout and flow rates Determine pipe
sizes
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