4) 2 kg of Refrigerant 134-a is contained in a constant volume tank as a saturated vapor. When it is heated, the refrigerant pressure and temperature become 400 kPa and 50°C, respectively. Determine the change of entropy of the refrigerant during this process. If the heat transfer is coming from a thermal energy reservoir at 100°C, what is the change in entropy of the thermal energy reservoir, and sum of the changes in entropy of refrigerant and the thermal energy reservoir?
5) A rigid tank, initially containing 1.5 kg of water vapor at 1.6 MPa and 400°C, is left to come to thermal equilibrium with its surrounding ambient at 25°C. Find the change in entropy of the water inside the tank, the change in entropy of the surrounding, and the sum of the changes in entropy of the water inside the tank and the surrounding.
6) In a water heating system, 3 kg of cold water at 3°C is mixed adiabatically with 4 kg of hot water at 90°C. What is the temperature of the mixed warm water, the total entropy of the mixed warm water, and the sum of the total entropy of cold and hot water?
7) Steam enters a turbine at 600°C and 6000 kPa and leaves the turbine as saturated vapor at 50 kPa. What is the isentropic efficiency of the turbine?
8) Air enters a turbine at 1000 K and 2 MPa and leaves it at 20 kPa. If the isentropic efficiency of this turbine is 75%, what is the air temperature at its exhaust?
9) Refrigerant 134-a enters a compressor as saturated vapor at -15°C and leaves at 1.3 MPa. The mass flow rate of the refrigerant is 1.5 kg/s. If the isentropic efficiency of the compressor is 80%, what is the power input to the compressor?