Question

Send somit Click Submit to complete this assessment. Question 4 p 4 uestion 4 30 points You need to pump water at 20°c from an open reservoir at flow rate of 1.4*103 m/s through a pipe with an inside diameter of 0.03 m, using a centrifugal pump having un (NPS)req - 2.5 m and the equivalent length on the suction side is 3 m. There are several minor losses: four standard 90 flanged elbows, and fully open fanged globe valve, fully open flanged gate valve, and the Entrance. What is the maximum distance above the water level in the reservoir that the pump can be located and will operate properly without cavitation? Vapor pressure of water at 20°c - 2.338 Kpu. Density of water -1000 Kg/m, dynumie viscosity of water 8.90 * 1012 r... (1 atm-101325 Pa).

Answer 1

Os O= 1.4x108 m/s. d= 0.03m 1.98 m/s. &= A. ) Vs ll A 14x10 3 (003) T 4 V=1.98 m/s V? 0.199 m VH = Velocity Head 2g VH = 0.199m

loss co-efficient tk) Minor Type loss Co-efficient (K) Head loss nck -KVH zg .v2 m. 0.3 goo - Flanged Elbow 4X0 3x 0.199 = 0.2388 m. Fully open Flanged 10 1x lox 0.199 1.99m. Globe Valve Fully open flanged 0.15 1 x 0 15x0.199 = 0.02985m. Gate valve Total Minor loss = 2.2586 m. Since velocity in pipe is very low, therefore major losses also Verg- very low [hme a v?], by neglecting them - hy = Friction loss = hmL + hmil Minor losses. j Major losses his = 2.258m Net positive suction Head is given Patm pv NPSH hs-hf 7.g $3 h = Suction Head Pv = Vapour Pressure Head. 89

101325 2338 2.5 = -hs-2.258 9.81x loco 9.01 x 1000 2-5 = 10.3287 - hs - 2.258 - 0-2383 hs = 10.3287 - (2-258 +0-2383 +2:5) hs 5.3323 m = This is the least suction Head Required to avoid Cavitation