Refrigerant-134a is compressed in a steadily operating adiabatic compressor of a…

Refrigerant-134a is compressed in a steadily operating adiabatic compressor of a vapor-compression refrigerator from a saturated-vapor inlet at −8 °C, where \(h_1=242.54\,\mathrm{kJ/kg}\), \(s_1=0.9377\,\mathrm{kJ/kg\cdot K}\) and \(v_1=0.09193\,\mathrm{m^3/kg}\), to a condenser pressure of \(1.200\,\mathrm{MPa}\). If the compression were internally reversible, the exit enthalpy would be \(h_{2s}=287.10\,\mathrm{kJ/kg}\). The actual compressor isentropic efficiency, defined as \((h_{2s}-h_1)/(h_2-h_1)\), is \(0.80\). Saturated liquid leaves the condenser at \(1.200\,\mathrm{MPa}\) with \(h_3=117.77\,\mathrm{kJ/kg}\) and is throttled isenthalpically into the evaporator. Kinetic and potential energy changes are negligible. The measured refrigeration capacity is \(45.0\,\mathrm{kW}\). Determine (a) the actual compressor-exit enthalpy, (b) the refrigerant mass flow rate, (c) the actual compressor power, (d) the condenser heat-rejection rate, and (e) the actual COP. Also compute the COP that would be obtained if the compressor were isentropic, using the same mass flow rate and the same condenser-exit and evaporator-inlet enthalpies.

\(\eta_s\) stretches the isentropic enthalpy rise into a larger actual rise; \(q_L\) still uses the evaporator enthalpies only.