Refrigerant-134a enters the coils of the evaporator of a refrigeration system as a saturated liquid–vapor mixture at a pressure of 140 kPa. The refrigerant absorbs 180 kJ of heat from the cooled space, which is maintained at –10°C, and leaves as saturated vapor at the same pressure. Determine the total entropy change for this process.

A vessel initially contains 5.0 kg of liquid water and 2.0 kg of ice at 0°C. Energy is added until the ice has just melted. The temperature at the boundary where heat transfer occurs is taken to be the system temperature during the process. The enthalpy of melting is 333.5 kJ/kg. Consider the following processes used to melt the ice. a. Heat is added from the environment at 20°C. Determine the entropy flux and the total entropy generation, both in kJ/K. b. Heat is added from a reservoir at 727°C. Determine the same quantities as in part (a). c. Paddle-wheel work is used to change the state. Determine the total entropy production for the process, in kJ/K. d. Comment on the relative degree of irreversibility for the three processes.

An adiabatic steam turbine is operating with inlet conditions of 12.5 MPa and 600°C and an exit pressure of 10 kPa. It has an isentropic efficiency of 85%. Determine the steam flow required if it is to produce 250 MW. Determine the exit temperature, the outlet quality (if the outlet conditions are a saturated mixture), and the change in entropy. Also show the process on a T-s diagram with respects to the saturation lines

Refrigerant 134a enters a compressor at 600 kPa as a saturated vapor. It exits at 60°C and 1.4 MPa. Determine the entropy change and the isentropic efficiency. Show the process on a T-s diagram with respects to the saturation lines.