8. A refrigeration unit was designed to maintain the temperature of a 500 m food storage at 7C. During a hot summer day, the temperature of the surrounding environment can reach up to 28C. The refrigerator uses a Carnot cycle and requires 20 kW of power. a. Sketch the cycle in a PV-diagram. Indicate the type of all processes and their direction. Further, indicate the total work of the cycle and its sign. In total, is the system absorbing heat or releasing heat? b. Calculate the coefficient of performance for this refrigerator COP = |Qin/Wint C. Calculate the cooling power that is achieved by this refrigeration I system. d. Nitrogen is used as the working fluid. Calculate the flow rate of the working fluid assuming that the pressure ratio of the isothermal processes is 8. e. Consider the adiabatic compression process of the cycle. First find the pressure ratio and then calculate the shaft power. Remember that nitrogen (c = (5/2)R) is used. f. The refrigerator discussed above is completely reversible. COPs for real refrigeration units are usually much lower. In the present case, COP is 7.5. Determine the power requirement for the cooling unit in this case. [Ans.(b) 13.33; (c) 267 kW; (d) 55 mol/s; (e) 1.29 834 kW; (6) 36 kW)