In cooling situations where the desired temperature range is large, two refrigeration cycles can be stacked to create a cascading refrigeration system that increases the cooling capacity compared to a single-cycle system. A cascade system using two ideal refrigeration cycles is used. The high-temperature cycle uses Refrigerant-134a with saturated liquid leaving the condenser at 40C and saturated vapor leaving the heat exchanger at -20C. The low-temperature cycle uses Refrigerant-23, which is suitable for use in the colder temperature conditions. Refrigerant-23 leaves the evaporator as a saturated vapor at -80C with h = 330 kJ/kg, saturated liquid leaves the heat exchanger at -10C with h = 185 kJ/kg, and the fluid leaves the compressor with h = 405 kJ/kg.
a.) Determine the ratio of the mass flow rates for the two cycles.
b.) Determine the coefficient of performance for the overall system.