Water at 20 0 C is pumped from the lower to the upper reservoir (Fig. P3.180). P
ID: 1850387 • Letter: W
Question
Water at 200
C is pumped from the lower to the upper reservoir (Fig. P3.180). Pipe friction losses
are approximated by
2
27 / 2
f
h V g ? , where V is the average velocity in the pipe. The pump
efficiency is 75%.
(a) If the flow rate is 1500 gal/min, calculate the required pump horsepower.
(b) If the pump has a performance curve as shown in Fig. P3.181, calculate the flow rate in
gal/min and the horsepower needed to drive the pump.
(c) Calculate the forces and moments exerted on the pump support pad for cases (a) and (b).
Explanation / Answer
Q = 1500 gpm / 448.8 gpm/ ft^3/s = 3.34 ft^3 / s . V = Q/A = 3.34 / pi (3/12)^2 = 17 ft/s h_f = 27 17^2 / 2x32.2 = 121 ft. From Bernoulli's equation: p1/ rho g + V1^2 / 2 + z1 = p2/ rho g + V2^2 / 2 + z2 + h_f - h_p 0 + 0 + 50 = 0 + 0 + 150 + 121 - h_p Thus, h_p = 221 ft. P_pump = P_$ = P_water / eta . P_water = rho g Q h_p P_pump = 62.4 lbf / ft^3 x 3.34 ft^3 / s x 221 ft / 0.75 = 61,600 ft lbf / s = 61,600 / 550 = 112 hp
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