A gas refrigeration system uses air as the working fluid has a pressure ratio of 4. Air enters the compressor at -7oC. The high-pressure air is cooled to 30oC by rejecting heat to the surroundings. It is further cooled to -15oC by regenerative cooling before it enters the turbine. Assuming both the turbine and the compressor to be isentropic and using the PG model for air, determine (a) the lowest temperature that can be obtained by this cycle, (b) the coefficient of performance (COPR) of the cycle and (c) the mass flow rate of air for a refrigeration rate of 12 kW. (d) What-if Scenario: What would the COP be if the pressure ratio were 5?