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Unformatted text preview: HOMEWORK SET 7b 9.44 A small pump is driven by a 2 kW motor with liquid water at 150 kPa, 10 ° C entering. Find the maximum water flow rate you can get with an exit pressure of 1 MPa and negligible kinetic energies. The exit flow goes through a small hole in a spray nozzle out to the atmosphere at 100 kPa. Find the spray velocity. Solution: C.V. Pump. Liquid water is incompressible so work from Eq.9.15 W . = m . w = m . v(P e P i ) ⇒ m . = W . / [v(P e P i ) ] = 2/[0.001003 ( 1000 – 150) ] = 2.35 kg/s C.V Nozzle. No work, no heat transfer, v ≈ constant => Bernoulli Eq.9.16 1 2 V 2 ex = v Δ P = 0.001 ( 1000 – 100) = 0.9 kJ/kg = 900 J/kg V ex = 2 × 900 J/kg = 42.4 m s 1 9.62 A condenser in a power plant receives 5 kg/s steam at 15 kPa, quality 90% and rejects the heat to cooling water with an average temperature of 17 ° C. Find the power given to the cooling water in this constant pressure process and the total rate of enropy generation when condenser exit is saturated liquid. Solution: C.V. Condenser. Steady state with no shaft work term. Energy Eq.6.12: m . h i + Q . = m . h e Entropy Eq.9.8: m . s i + Q . /T + S . gen = m . s e Properties are from Table B.1.2 h i = 225.91 + 0.9 × 2373.14 = 2361.74 kJ/kg , h e = 225.91 kJ/kg s i = 0.7548 + 0.9 × 7.2536 = 7.283 kJ/kg K, s e = 0.7548 kJ/kg K = 0....
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This homework help was uploaded on 04/10/2008 for the course ME 235 taught by Professor Borgnakke during the Spring '07 term at University of Michigan.
 Spring '07
 Borgnakke

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