Concept explainers
The radiator of a steam heating system has a volume of 20 L and is filled with superheated water vapor at 200 kPa and 200°C. At this moment both the inlet and the exit valves to the radiator are closed. After a while it is observed that the temperature of the steam drops to 80°C as a result of heat transfer to the room air, which is at 21°C. Assuming the surroundings to be at 0°C, determine (a) the amount of heat transfer to the room and (b) the maximum amount of heat that can be supplied to the room if this heat from the radiator is supplied to a heat engine that is driving a heat pump. Assume the heat engine operates between the radiator and the surroundings.
FIGURE P8–31
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Chapter 8 Solutions
EBK THERMODYNAMICS: AN ENGINEERING APPR
- A frictionless piston-cylinder device initially contains 200L of saturated liquid refrigerant-134a. The piston is free to move and its mass is such that it maintains a pressure of 900 kPa on the refrigerant. The refrigerant is now heated until its temperature rises to 70C. Calculate the work done during this process. ANS. 5571 KJA 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?arrow_forwardWater vapor at 110 kPa and 150°C is contained in a rigid vessel tank. At what temperature will the vapor start to condense when the container is cooled slowly? How much heat will have to be removed per kilogram in this cooling process?arrow_forwardA 14-ft3 tank contains oxygen initially at 14.7 psia and 80°F. A paddle wheel within the tank is rotated until the pressure inside rises to 20 psia. During the process 20 Btu of heat is lost to the surroundings. Determine the paddle-wheel work done. Neglect the energy stored in the paddle wheel. The gas constant and molar mass of oxygen are R = 0.3353 psia-ft3/lbm-R and M = 32 lbm/lbmol. The specific heat of oxygen at the average temperature of Tavg = (735+540)/2= 638 R is cv,avg= 0.160 Btu/lbm.R. The paddle-wheel work done is Btu.arrow_forward
- Consider a vessel which has a resistance heater and a mixer. is filled with 3.6 kg of saturated water vapor at 120°C. Then the heater and mixer are put to work, the water vapor is compressed, and there is 5 kg of heat loss to the air from the surroundings. At the end of the process, the temperature and pressure of the water vapor in the vessel are measure, and they turn out to be 300°C and 500 kPa. Determine: a) The net energy transfer, in kJ, to the water vapor during this process.arrow_forwardAn isolated piston-cylinder device contains 5 L of saturated liquid water at a constant pressure of 175 kPa. The water is stirred with a paddle wheel while a current of 8 A flows for 45 minutes through a resistor placed in the water. If theHalf of the liquid evaporates during this process at constant pressure and the work done by the paddlewheel is equal to 400 kJ, determine the voltage of the source. Also, show the process on a P-v diagram with respect to the saturation lines.arrow_forwardThe radiator of a steam heating system has a volume of 150L and is filled with superheated vapor at 200kPa and 200C. 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 kPaarrow_forward
- A piston-cylinder device contains 0.850 kg of refrigerant-134a at –10.0°C. The piston that is free to move and has a mass of 12.0 kg and a diameter of 25.0 cm. The local atmospheric pressure is 88.0 kPa. Now, heat is transferred to refrigerant-134a until the temperature is 15.0°C. Determine (a) the final pressure, (b) the change in the volume of the cylinder, and (c) the change in the enthalpy of the refrigerant- 134a. Assume the following: va-10°C = 0.2302 m³/kg, va-15°C = 0.2544 m³/kg, ha-10°C = 247.22 kJ/kg, h@15°C = 268.18 kJ/kgarrow_forwardHi! A 14-ft3 tank contains oxygen initially at 14.7 psia and 80°F. A paddle wheel within the tank is rotated until the pressure inside rises to 20 psia. During the process 20 Btu of heat is lost to the surroundings. Determine the paddle-wheel work done. Neglect the energy stored in the paddle wheel. The gas constant and molar mass of oxygen are R = 0.3353 psia·ft3/lbm·R and M = 32 lbm/lbmol. The specific heat of oxygen at the average temperature of Tavg = (735 + 540)/2 = 638 R is cv ,avg= 0.160 Btu/lbm·R. The paddle-wheel work done is Btu. ANSWERarrow_forwardA frictionless piston-cylinder device contains 0.25kg of saturated vapor refrigerant 134a at 200kPa. The refrigerant is heated by passing current through an electrical heated rated at 220V and 5 A for period of 30 Second. During the process 15 kJ of heat is transferred from the refrigerant to the surrounding air. Sketch the process on a T-v diagram and determine: The final temperature of the refrigerant, °C. The boundary work during the process, kJarrow_forward
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