7-22 7-58 A commercial refrigerator with R-134a as the working fluid is considered. The evaporator inlet and exit states are specified. The mass flow rate of the refrigerant and the rate of heat rejected are to be determined. QH Assumptions 1 The refrigerator operates steadily. 2 The kinetic and potential energy changes are zero. Condenser Properties The properties of R-134a at the evaporator inlet and exit states are (Tables A-11 through A-13) P1 x1 P2 T2 Expansion valve 120 kPa ½ ¾h1 65.38 kJ/kg 0.2 ¿ 120 kPa ½ ¾h2 238.84 kJ/kg 20qC ¿ Evaporator 120 kPa x=0.2 Analysis (a) The refrigeration load is Q L (COP)W in Win Compressor QL 120 kPa -20qC (1.2)(0.45 kW) 0.54 kW The mass flow rate of the refrigerant is determined from m R Q L h2 h1 0.54 kW (238.84 65.38) kJ/kg 0.0031 kg/s (b) The rate of heat rejected from the refrigerator is Q H Q L W in 0.54 0.45 0.99 kW PROPRIETARY MATERIAL. © 2008 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and educators for course preparation. If you are a student using this Manual, you are using it without permission.

Download
# 7-22 exit states are specified. The mass flow rate of the... 7-58