Question

A water pump delivers 6 hp of shaft power when operating. The pressure differential between the outlet and the inlet of the pump is measured to be 1.2 psi when the flow rate is 15 ft3/s, and the velocity doubles from 3 ft/s as the water passes through the pump. Determine the mechanical efficiency of this Dumn

Answer 1

Given Power of pump W 6 hp Pressure difference between outlet and inlet of the pump is AP 1.2 psi Flow rate of water Q 1.5 ft'/s To determine the mechanical efficiency of the pump, we need to know the increase in the mechanical energy of the fluid as it flows through the pump, which is Apply energy balance, AE mech fluid emech,out emech,in Р. И P2 V ΔΕ 'mech,fluid g2 +Z18 2 + m -m 2 P Neglecting datum head effect, the equation reduces as, PA P2 AE mech,fluid m 2 = m 2 VV P2 P1 +(pO) ΔΕ. mech.fluid(PO) 2 2 P VV ()AP+(pQ) 2 2 .-efam|_ ...1) (p) 2 ΔΕ, 'mech.fluid

Since the final velocity is double of initial velocity, -2x3 - 6 ft/s Thus, from equation (1); V-V mech fud APl+(p) 2 (6 ft/s-(3 fts) 144 in.1.94 slug/ft' 2 lb 1.2 in. X mech fiuld 15 f3/. ft2 2 AE 2984.85 lb ft mech, fluid The mechanical efficiency of the pump becomes as, AE 'mech,fluid pump W pump,shaft 2984.85 lb ft x100 550 lb ft 6 hpx hp = 90.45% l pump