The vapor compression heat pump operates at steady state using Refrigerant 22, w

Question

The vapor compression heat pump operates at steady state using Refrigerant 22, whose flow rate is 6kg/min. The heat pump maintains the interior of a house at 25 C, while drawing heat from the surrounding at a temperature of 10 C. The refrigerant enters the compressor as saturated vapor at -10 C, exits the compressor at 1 MPa and 50 C, and flows through the condenser at constant pressure existing as saturated liquid. The compressor operates adiabatically. Calculate (a) the power required by the compressor in kW (b) the isentropic compressor efficiency (c) the rate of heat transferred to the interior of the house in kW

Explanation / Answer

Here at T4 = -10 C , h4 = hg = 401.2 KJ/kg and s4 = sg = 1.766 KJ/Kg.Knwow s1 = s2 = 7.66 KJ/Kg.K as 4-1 is isentropic assumedso At P1 = 12 bar and s1 = 1.766 KJ/Kg.K, from table of R-22, we get : h1 = 431.4 KJ/Kgso a) compressor work = m.(h1 - h2) = 0.8 x ( 431.4 - 401.2) = 24.16 KWbut actual work of compression = 24.16/0.75 = 32.21 KWb) now h2 = hf + x.hfg at 12 bar = 236.6 + 0.1 x 178 = 254.4 KJ/Kgso heat transferred from working fluid = m.(h1 - h2) Q1 = 0.8 x ( 431.4 - 254.4) = 141.6 Kwc)

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