Cengel & Boles -- Chapter 3 questions

3-89C Is the energy required to heat air from 295 to 305 K the same as the energy required to heat it from 345 to 355K? Assume the pressure remains constant in both cases.

3-91C A fixed mass of an ideal gas is heated from 50 to 80 C at a constant pressure of (a) 1 atm and (b) 3 atm.

For which case do you think the energy required will be greater?

3-93C A fixed mass of an ideal gas is hated from 50 to 80 C (a) at a constant volume and (b) at a constant pressure.

For which case do you think the energy required will be greater?

3-97C Is it possible to compress an ideal gas isothermally in an adiabatic piston-cylinder device?

3-35 A mass of 5kg of saturated water vapor at 200 kPa is heated at constant pressure until the temperature reaches 300 C.

Calculate the work done by the steam during this process.

3-37 A frictionless piston-cylinder device contains 8 kg of superheated water vapor at 500 kPa and 300 C. Steam is now cooled at constant pressure until 70 percent of it, by mass, condenses.

Determine the work done during this process.

3-38 A mass of 1.2kg of air at 150 kPa and 12 C is contained in a gas-tight, frictionless piston-cylinder device. The air is now compressed to a final pressure of 600 kPa. During the process heat is transferred from the air such that the temperature inside the cylinder remains constant.

Calculate the work done during this process.

3-48 A piston-cylinder device with a set of stops contains 10 kg of refrigerant-12. Initially, 8 kg of refrigerant is in the liquid form, and the temperature is -10 C. Now heat is transferred slowly to the refrigerant until the piston hits the stops, at which point the volume is 400 L.

Determine (a) the temperature when the piston first hits the stops and (b) the work done during this process. Also show the process on a P-V diagram.

3-73 The radiator of a steam heating system has a volume of 20 L and is filled with superheated vapor at 300 kPa and 250 C. At this moment both the inlet and exit valves to the radiator are closed.

Determine the amount of heat that will be transferred to the room when the steam pressure drops to 100 kPa. Also show the process on a P-v diagram with respect to saturation lines.

3-78 A piston-cylinder device contains 5kg of refrigerant-12 at 800 kPa and 60 C. The refrigerant is now cooled at constant pressure until it exists as a liquid at 20 C.

Determine the amount of heat transfer, and show the process on a T-v diagram with respect to saturation lines.