GATE 2016 ME (ME2) – Question 56
An ideal vapour-compression refrigerator uses R-134a between 0.14 MPa and 0.8 MPa with refrigerant mass flow 0.05 kg/s. The rate of heat rejection to the environment is ______ kW. Data: at 0.14 MPa saturated vapour h = 236.04 kJ/kg, s = 0.9322 kJ/kg K; at 0.8 MPa superheated vapour h = 272.05 kJ/kg, s = 0.9322 kJ/kg K; at 0.8 MPa saturated liquid h = 93.42 kJ/kg.
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Correct answer: 8.90 to 8.95
Explanation
Ideal compression is isentropic, so use the given0.8MPa superheated-vapour enthalpy272.05kJ/kg at the inlet entropy. Condenser exit saturated-liquid enthalpy is93.42kJ/kg. Heat rejection rate is mass flow times their difference:0.05(272.05−93.42)=**8.9315kW**.