Chapter 7, Problem 7.22P

Question 2 Three kilograms of water in a piston-cylinder assembly, initially at 100 kPa and 75°C, are heated at constant pressure with no internal irreversibilities to a final temperature of 500°C. For the water, Plot the processes on the P-v curve and determine: (a) the change in exergy, (b) the exergy transfer accompanying heat transfer, (c) the exergy transfer accompanying work, and (d) the exergy destruction. Take To = 25 °C, Po = 100 kPa and ignore the effects of motion and gravity.

Consider 5.2 pounds per minute of water vapor at 100 lbf/in², 500°F, and a velocity of 100 ft/s entering a nozzle operating at steady state and expanding adiabatically to the exit, where the pressure is 40 lb/in². The isentropic nozzle efficiency is 85.0%. Determine the velocity of the steam at the exit, in ft/s, and the rate of entropy production, in Btu/min.°R. Step 1 Determine the velocity of the steam at the exit, in ft/s. Your answer is correct. V₂ = 1907.37033530460465 ft/s Hint Step 2 * Your answer is incorrect. Determine the rate of entropy production, in Btu/min.°R. Attempts: 2 of 3 used

Refrigerant 134a at 15 oC, 1.8 bar, and a mass flow rate of 5 kg/min enters an insulated compressor operating at steady state and exits at 5 bar. The isentropic compressor efficiency is 77%. Neglect the changes in kinetic and potential energies and assume the surroundings to be at 25 °C.Determine:S 1.1  the temperature of the refrigerant exiting the compressor, 1.2  the power input to the compressor, in kW, and 1.3  the rate of exergy destruction, in kW.

Saturated water vapor at 300°F enters a compressor operating at steady state with a mass flow rate of 5 lb/s and is compressed adiabatically to 700 Ibf/in.? If the power input is 2150 hp, determine for the compressor: (a) the percent isentropic compressor efficiency and (b) the rate of entropy production, in hp/°R. Ignore kinetic and potential energy effects.

Water vapor at 6 MPa, 500°C enters a turbine operating at steady state and expands to 20 kPa. The mass flow rate is 3 kg/s, and the power developed is 2626 kW. Stray heat transfer and kinetic and potential energy effects are negligible. Determine: (a) the isentropic turbine efficiency and (b) the rate of entropy production within the turbine, in kW/K. Show this compression process on a T-s diagram.

A mass of 0.05 kg of carbon dioxide (molar mass 44 kg/ kmol, gamma 1.3), occupying a volume of .03 m3 at 1.025 bar, is compressed reversibly until the pressure is 6.5 bar. Determine the final temperature, the work done on the CO2, and the heat supplied: (1) When a process is isothermal.

An ideal gas initially at 550 K and 9 bar undergoes a four-step mechanically reversible cycle in a closed system. The pressure decreases isothermally to 3 bar; then pressure decreases at constant volume to 1.5 bar; (after that) volume decreases at constant pressure. Finally, the gas returns adiabatically to its initial state. (a) Sketch the cycle on a PV diagram and (b) Calculate Q, W, and AH for each step of the cycle.

1. 1 kg of propane contained within a piston-cylinder assembly undergoes a process from an initial state of Pi = 15 bar and X = 50% to a final state of P2 =4 bar, T2 = 24°C. The work done by the propane during the process is 50 kJ, and heat transfer to the surroundings occurs at a surface with an average temperature of 47°C. Kinetic and potential energy changes can be neglected. Determine the entropy production of the system (kJ/K).

Four kilograms of a two-phase liquid-vapor mixture of water initially at 300°C and x, = 0.5 undergo the two different processes 7.33 described below. In each case, the mixture is brought from the initial state to a saturated vapor state, while the volume remains constant. For each process, determine the change in exergy of the water, the net amounts of exergy transfer by work and heat, and the amount of exergy destruction, each in kJ. Let To = 300 K, Po =1 bar, and ignore the effects of motion and gravity. Comment on the difference between the exergy destruction values. a. The process is brought about adiabatically by stirring the mixture with a paddle wheel. Answer b. The process is brought about by heat transfer from a thermal reservoir at 610 K. The temperature of the water at the location where the heat transfer occurs is 610 K Answer