Question

Problem 2 (20 points): Tests by the Byron Jackson Co. of a 14.62-in-diameter centrifugal pump at 2134 r/min yield the following data for water at 20°C Q (ft/s) 2 4 6 8 10 H (ft) 340 340 340 330 300 220 bhp 135 160 205 255 330 330 a) Determine the best efficiency point and the maximum efficiency b) The measured NPSHR at BEP is 16 ft and the friction loss between the inlet and the pump is 22 ft. Will it be sufficient to avoid cavitation if the pump inlet is placed 9 ft below the surface of a sea-level reservoir?

Answer 1

Solution Given Data :- D = 14.62 in, N= 2134 &/min, T=20°C. At T= 20°C = X=89= 62.35 16/873, va por pressure Py = 49.2 16/442 * The efficienies at each flow rate is computed I by using formula n= P90HK (550) (bhp) Q 16/ H 18t) bhp _ 0 2 4 6 8 10 340 340 330 330 300 220 135 160 205 255 330 | 390 lo10.48210.752 0.88 10.825 0.756. computedl. a) — As we is af Maximum can see the maximum efficiency point ® 64s ( close to 6 673/s) of efficiency is n0.88 88% Lactual. = -96% (below the sea surface) > To avoid cavitation NPSH < Po-Pu-L-RE Tiit Ś PaiPu = NPSH - he inz § 2116 — 49.2 – 16-22 jatm = 2116 16 7 612/ 19 62.35 gives i Z 3-4.852 ft . by keeping the pump q ft below the surface 4.1481 06_marign' against cavitation. Hence it is subficient to avoid cavitation.