In: Mechanical Engineering
A cooling plant adopted a two-stage cascade refrigeration system
to meet the required cooling load. In both upper and lower cycles,
the refrigerant leaves condenser as saturated liquid and enters
compressor as saturated vapor. The isentropic efficiency of the
upper cycle compressor is 80 %, while the lower cycle compressor is
70% efficient. The pressure limits of the upper and lower cycles
are 1 MPa and 0.2 MPa with refrigerant-134a, respectively. Heat
rejection from the lower cycle to the upper cycle takes place in an
adiabatic counterflow heat exchanger where the lower cycle enters
about at 0.5 MPa and the upper cycle enter about at 0.32MPa. If the
mass flow rate of the refrigerant in the upper cycle is 0.28 kg/s,
determine
i. the mass flow rate of the refrigerant in the lower cycle
ii. the rate of heat removal from the refrigerated space and the
power input into the compressors
iii. the COP of the refrigerator,