Civil Engineering MCQJE Level Civil Engineering
For a centrifugal pump, the affinity laws state that when speed changes from N1 to N2:
Fluid MechanicsFluid MechanicsMEDIUM
Choose the correct answer
A
Q ∝ N², H ∝ N, P ∝ N³
B
Q ∝ N, H ∝ N², P ∝ N³
C
Q ∝ N, H ∝ N, P ∝ N
D
Q ∝ N³, H ∝ N², P ∝ N
Correct Answer
B. Q ∝ N, H ∝ N², P ∝ N³
Why is this the answer?
Affinity laws (pump similarity): Q ∝ N; H ∝ N²; P ∝ N³. If N doubles: flow doubles, head quadruples, power increases 8×. Used for variable speed pumps (VFD control). Also: for geometrically similar pumps of different size at same speed: Q ∝ D³, H ∝ D², P ∝ D⁵.
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