q7 Refrigerant -134a enters the compressor of a refrigerator as superheated vapo
ID: 1858639 • Letter: Q
Question
q7
Refrigerant -134a enters the compressor of a refrigerator as superheated vapor at 0.14 MPa and -10 degree C at a rate of 0.111 kg/s, and it leaves at 0.7 MPa and 50 degree C. The refrigerant is cooled in the condenser to 24 degree C and 0.65 MPa, and it is throttled to 0.15 MPa. Disregarding any heat transfer and pressure drops in the connecting lines between the components, determine the rate of heat removal from the refrigerated space and the power input to the compressor, QL = kW (Round to one decimal place) Win = kW ( Round to two decimal places) (b) the isentropic efficiency of the compressor, eta C = % (Round to one decimal place) and (c) the COP of the refrigerator. COPr = (Round to two decimal places)Explanation / Answer
mass flow rate = 0.111 kg/sec
State 1 : P1 = 0.14 MPa and T1 = -10 C
From property table of R0134a; h1 = 246.36 KJ/Kg ; s1 = 0.9724 KJ/Kg-K
State 2 : P2 = 0.7 MPa and T2 = 50 C
From property table of R0134a; h2 = 288.53 KJ/Kg ; s2 = 0.9954
State 3 : P3 = 0.65 MPa and T3 = 24 C (Saturate state)
From property table of R0134a; h3 = 85.26 KJ/Kg
State 4: h4 = h3 = 85.26 KJ/Kg (isenthalpic process)
a)QL = m*(h1-h4) = 17.8821 KW
b)Win = m*(h2-h1) = 4.68087 KW
c)isentropic efficiency = Ws/Wa = (281.21-246.36)/(288.53-246.36) = 82.64%
d)COP = QL/W = h1-h4/h2-h1 = 3.82
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