1. Air is to be compressed from 1 atm and 298 K to 8 atm at a rate of 20,000 L/min. (a) Determine if this process should be done with a (i) isentropic process, (ii) polytropic process with n=1.25, or (iii) isothermal process. (b) Show all three processes on one P-v diagram.
2. (a) Why is the outlet state of a turbine, compressor, or pump always to the right of the inlet state on a h-s diagram? (b) Draw h-s diagrams for a turbine, compressor, and pump (three total). Show the actual and ideal processes on the h-s diagram for each device.
3. Air expands steadily through an adiabatic turbine from 10 atm, 600 K to 1 atm. (a) Calculate the work (kJ/kg) developed by the turbine if the isentropic efficiency is 85%. (b) Calculate the work (kJ/kg) developed by the turbine if the process is isentropic. (c) Draw one T-s diagram showing both processes.
4. Steam expands steadily through an adiabatic turbine from 1 MPa, 350 °C to 100 kPa. (a) Calculate the work (kJ/kg) developed by the turbine if the isentropic efficiency is 85%. (a) Calculate the work (kJ/kg) developed by the turbine if the process is isentropic. (c) Draw one T-s diagram showing both processes.
5. Nitrogen gas enters an adiabatic nozzle with negligible velocity, 300 kPa, 800 K and exits at 200 m/s. For a nozzle isentropic efficiency of 80%, calculate the exit temperature (K).
6. In heavy duty diesel engine dynamometer testing, the air-to-air intercooler is replaced with a liquid-toair heat exchanger. In the laboratory heat exchanger, air enters one side of the exchanger at a rate of 1000 L/s, 400 K, 2.5 atm and exits at 325 K. Water enters the other side of the exchanger at 1.5 L/s, 25 °C, and 3 atm. Neglecting any pressure drop through the exchanger, (a) determine the rate of heat transfer (kW) between the air and water and (b) the rate of entropy generation (kW/K).
7. The combustion gases (modeled as air) enter a turbine at 6 atm, 1000 K and exits at 1 atm, 500 K. Determine the isentropic efficiency 8. A hot steel bar is to be cooled by immersing the bar in water. A well insulated 0.5 m3 rigid tank contains water at 20 °C and 1 atm. The 10 kg bar, initially at 90 °C, is placed in the tank and the tank sealed. Determine (a) the final temperature (°C) of the bar and (b) entropy generation of this system (kJ/K).
9. Calculate the entropy generation (kJ/K) for the system in the homework problem 10 if the heat transfer occurs at 800 °C.