Question

4. The discharge pressure gauge reading is 5 lb/in2 (psi) for the pumping system shown in the sketch below, with the outlet nozzle discharging a 2-inch diameter stream of water directly to the atmosphere. The gauge pressure at the pump suction inlet at the point of incipient cavitation is (-2,071.12) lb/ft, i.e., for vapor pressure of water at 68° F of 50.54 lb/ft2 absolute, and standard atmospheric pressure 30 in Hg. Friction losses in the suction piping from the reservoir to the pump inlet connection total 0.03(LIDVsuction)2/2g], and friction losses in the discharge piping and outlet nozzle may be neglected. Use a specific weight of water, at 68° F, of y 62.3 lb/t3. Determine the length of the suction pipe, power input to the water by the pump, and the fraction of the power input needed to overcome frictions losses in the suction piping. [Hints: (a) first apply the Continuity and Energy Equations across the outlet nozzle to determine the discharge, (b) apply the Energy Equation between the reservoir water surface and the pump suction inlet to establish the length of the suction pipe and the head loss in the suction pipe, and (c) apply the Energy Equation across the pump to determine the power input.] 2-in. diam 6-in. diam 4-in. discharge pipe 10 ft Free jet Water 68 F

Answer 1

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