申論題

4. (10%) A refrigeration system cools a steel casting from 25℃ to -15℃ at a rate of 15 kg．s^-1 Assume that heat flows from the refrigeration system to the surroundings at a temperature of 45℃ and the specific heat capacity of the steel casting is 7.6 kJ．kg^-1.℃^-1. If the thermodynamic efficiency of the process is 31%, determine the power (kJ/kg) requirement of the system?