Concept explainers
(a)
The flow rate and power required when both the pumps are running.
Answer to Problem 11.75P
When both the pumps are running the flow-rate is
Explanation of Solution
Given information:
Water temperature = 20° C
The pump size = 35 inch = 88.9 cm
The density of water = 998 kg/m3
All other system losses can be neglected.
Calculation:
Let us assume following values.
The density of water = 998 kg/m3.
The value of dynamic viscosity =
For the cast iron,
The 35-inch pump has the curve fit head relation
The two pumps are connected in parallel, so, each pipe takes half of the total volume flow rate.
The velocity of flow is given by
And, the change in elevation is,
Putting values in equation (1):
The value of Q is to be iterated till both pump head and system head become equal.
By iterative calculations, at
Now, the total power required is
Under BEP operation conditions,
Conclusion:
Thus, when both the pumps are running the flow-rate is:
(b)
The flow-rate and power, when one of the pumps is shut off and isolated.
Answer to Problem 11.75P
When one of the pumps is shut off and isolated, the flow-rate is
Explanation of Solution
Given information:
RPM of the pump = 3500 rpm.
Water temperature = 20° C
Diameter of the pipe = 5 inch = 12.7 cm.
Length of the pipe = 2195 m.
All other system losses can be neglected.
Calculation
Let us assume following values
The density of water = 998 kg/m3.
The value of dynamic viscosity =
For the cast iron,
The 35-inch pump has the curve fit head relation
The two pumps are connected in parallel, so, each pipe takes half of the total volume flow rate.
The velocity of flow is given by
And, the change in elevation is,
Putting values in equation (1):
The value of Q is to be iterated till both pump head and system head become equal.
By iterative calculations, at
Now, the total power required is:
Under BEP operation conditions for single pump,
Conclusion:
Thus, when one of the pumps is shut off and isolated, the flow-rate is
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Chapter 11 Solutions
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