Chemical Thermodynamics

7. By steadily circulating a refrigerant at low temperature through passages in the walls of the freezer compartment, a refrigerator maintains the freezer temperature at -4°C when the air surrounding the refrigerator is at 25°C. The rate of heat transfer from the freezer compartment to the refrigerant is 8750 kJ/h and the power input required to operate the refrigerator is 3500 kJ/h. Determine the coefficient of performance of the refrigerator and compare with the coefficient of performance of a reversible refrigeration cycle operating between reservoirs at the same temperatures. [MO1, MO4, MO5, MO6]

5. Water vapor enters a turbine at 6 MPa and 400°C, and leaves the turbine at 200 kPa with the same specific entropy as that at the inlet. Calculate the difference between the specific enthalpy of the water at the turbine inlet and exit. [MO3, MO5]

6. A 1.00 ft³ well insulated rigid can initially contains refrigerant 134a at 90 psia and 30°F. Now a crack develops in the can and the refrigerant starts to leak out slowly. Assuming the refrigerant remaining in the can has undergone a reversible, adiabatic process, determine the final mass in the can when the pressure drops to 15 psia. [MO1]

7. Steam enters a turbine at a flow rate of 7.5 kg/s at a temperature of 600°C and a pressure of 10 MPa. The steam exits at a pressure of 100 kPa. The isoentropic efficiency of the turbine is 0.80. Determine the power output from the turbine, assuming that it is insulated. [MO3, MO5, MO6]

8. Liquid water enters an adiabatic pump at 20°C and 100 kPa, at a flow rate of 3.5 kg/s. The water exits at 2000 kPa. The isentropic efficiency of the pump is 0.75. Determine the power consumed by the pump. [MO3, MO5, MO6]

9. Refrigerant 134a at p₁ = 30 lbf/in², T₁ = 40°F enters a compressor at a steady state with a mass flow rate of 300 lb/h and exits as saturated vapor at p2 = 160 lbf/in². Heat transfer occurs from the compressor to its surroundings, which are at To = 40°F. Changes in kinetic and potential energy can be ignored. The power input to the compressor is 3 hp. Determine the heat transfer rate for the compressor, in Btu/hr, and the entropy production rate for the compressor, in Btu/hr.°R. [MO3, MO7]

5. A power cycle operating between two thermal reservoirs receives energy QH by heat transfer from a hot reservoir at TH = 2000K and rejects Qc by heat transfer to a cold reservoir at Tc = 400K. For each of the following cases, determine whether the cycle operates reversibly, operates irreversibly, or is impossible. [MO1, MO5, MO6] a. QH b. QH c. QH = 1000kJ, Wycle = 850kJ 1000kJ, E = 60% 1000kJ, Qr= 200kJ

3. A steam power plant with a power output of 200 MW consumes coal at a rate of 700 tons/h. If the heating value of the coal is 40,000 kJ/kg, determine the overall efficiency of plant. [MO1, MO3, MO5]

1. Use the steam tables to evaluate the entropy departure function for steam at 25 MPa and 850°C.

6. An engineer proposes to develop a power plant (which can be modeled as a heat engine) that will operate at an efficiency of 70%. The steam flowing through the power plant reaches a peak temperature of 750°F and rejects heat to the environment at a temperature of 70°F. Is this proposed power plant feasible, or does it violate the second law of thermodynamics? [MO1, MO3, MO5]