Question

A centrifugal pump is placed above a reservoir as shown below. If the NPSHR is 17 ft and the flow rate is 32 ft3/s, determine the maximum height, 21, that the pump can be located above the reservoir surface without cavitation. Assume that the total head loss between the tank and pump inlet is 10 ft. The diameter of the pipe on the suction side of the pump is 12 inches. The reservoir surface is at atmospheric pressure, Patm = 14.7 psia. Use the following values for water at 20°C: pv = 0.4 psia, p = 1.94 slug/ft?. Express your answer in feet. (2) Reference plane 21 P1 = Patm (1)

Answer 1

Given data NPSHR=17ft 8= 32 ft3/ Eh = loft de 12 inches ..A= T de A d2 Лх 4 D ? 12 4 ft

Patm -z,-Ehe-Pv r Υ Available NPSH is given by NPSHA To calculate the maximum height Zi, NPSHa =NPSHR (2) mone Patm - Ehl-Py - NPSHR r r Given data ft2 Patm = 14.7 Psia = 14.78 14 4=2116.8 lb At 2oc, pr=0.4 Psia ,S=1.94 slug :. Pv=57.6 lb/ft? Ft3 NPSHR = 17ft 8= 32 ft²/s

Refer to table B. 1 (Book-Fondamentals of fluid Mechanics by David r = 62.22 lb/ft² young) : Ziman -17 6.095 Ft = 2116.8 – 10 – 57.6 62.22 62.22

Please note that I have directly taken the value of gamma from table B.1. You can also convert the given 1.94 slug/ft3 into lb/ft3. That value will be 62.417 lb/ft3. Using this value the value of z1max will be 5.99 Ft.
Hence Answer is 6 ft.

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