Class Notes (806,815)
Engineering (154)
ENGG 2230 (29)
Lecture

# review solutions_ch11.pdf

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School
University of Guelph
Department
Engineering
Course
ENGG 2230
Professor
Bahram Gharabaghi
Semester
Winter

Description
Chapter 11: Problem Solutions 11.22 A 37-cm-diameter centrifugal pump, running at 2140 rev/min with water at 20C produces the following performance data: Q, m /s: 0.0 0.05 0.10 0.15 0.20 0.25 0.30 H, m: 105 104 102 100 95 85 67 P, kW: 100 115 135 171 202 228 249 : 0% 44% 74% 86% 92% 91% 79% (a) Determine the best efficiency point. (b) Hlot C verQus C . (c) If we desire to use this same pump family to deliver 7000 gal/min of kerosene at 20C at an input power of 400 kW, what pump speed (in rev/min) and impeller size (in cm) are needed? What head will be developed? Solution: Efficiencies, computed by   gQH/Power, are listed above. The best efficiency 3 point (BEP) is approximately 92% at Q  0.2 m /s. Ans. (a) P11.23 At what speed, when pumping water, should the 41.5-inch pump of Fig. 11.7b be run to realize, at highest efficiency, (a) a head of 100 ft? For this condition, what are the resulting (b) flow rate, and (c) brake horsepower? Solution: This is the same pump, same fluid, henc1  2  and1D = 2 . Thus the scaling from Eqs. (11.28) is relatively simple. First read the 41.5-inch BEP values as best the writer can:   89% ; n1 710 r/ min ; H 1 270 ft ; Q 1 21500 gal/min ; P 1 1650 bhp Then get the new rotation rate from the new head, using Eq.(11.28): H n D n 2  ( 2 ) ( 2)  100 ft ( 2 ) , n  710(100)1/2 430 r An.s()a H1 1 D 1 270ft 710 2 270 min Theflowrate andpowerfollowinlikemanner: Q2 Q 2 n2 D 2 3 430 430 gal   ( )  , Q 2 (21500)( )  13,000 Ans.(b) Q1 21500gpm n1 D1 710 710 min P P  n D 430 2  2  ( 2 )( 2) ( 2 )  ( ) , P 2 (1650)(0.222)  370 bhp Ans.( c) P1 1650bhp 1 n1 D1 710 Thesenumbers areslightlyuncertainbecauseofthedifficultyof readingFig.11.7b. P11.26 Would the smallest, or the largest, of the seven Taco Inc. pumps in Fig. P11.24 be better (a) for producing, near best efficiency, a water flow rate of 600 gal/min and a head of 95 ft? (b) At what speed, in r/min,
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