How to solve question 24 in the afternoon session of the 2011 case?
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24. Use a centrifugal pump to draw water from a cylindrical pool. The pool has a diameter and depth of 4 meters, and it is filled with clean water. The height of the pump suction inlet centerline above the ground is 0.5 m. The allowable net positive suction head (NPSHr) of the pump is 4 m. Under normal temperature and standard atmospheric pressure, the pressure loss in the inlet piping system is assumed to be 1 meter of water column. To prevent cavitation in the pump, a safety factor of 1.3 is adopted. What is the maximum volume of water (in m3) that this pump can pump, according to the following options? (A) 38.5 (B) 41.5 (C) 47.7 (D) 50.2 Thank you!
Hg = (P1 – PV) / (ρg – 1.3NPSHr – ∑hf) = (101.33 – 3.16789)×10^3 / (1000×9.81) – 4×1.3 – 1 = 3.8 m
H = Hg – z = 3.8 – 0.5 = 3.3 m
V = 0.785D^2H = 0.785×4^2×3.3 = 41.45 m^3
H = Hg – z = 3.8 – 0.5 = 3.3 m
V = 0.785D^2H = 0.785×4^2×3.3 = 41.45 m^3
The original poster’s calculation is correct! Think of it that way!