A gas refrigeration cycle with a pressure ratio of 4 uses helium as the working fluid. The

Question:

A gas refrigeration cycle with a pressure ratio of 4 uses helium as the working fluid. The temperature of the helium is 26oC at the compressor inlet and 50oC at the turbine inlet. Assuming isentropic efficiencies of 85 percent for both the turbine and the compressor, determine
(a) The minimum temperature in the cycle.
(b) The coefficient of performance.
(c) The mass flow rate of the helium for a refrigeration rate of 25 kW.