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Heat and Piston Cylinder Device

Individual Assignment. Each student is required to complete the task in a full handwriting on an A4 paper. Due Date of Submission on 30th November 2011, before 2. 00 PM. Late submissions will not be entertained. 1. A 1. 8-m rigid tank contains steam at 220°C. One third of the volume is in the liquid phase and the rest is in the vapor form. Determine (a) the pressure of the steam, (b) the quality of the saturated mixture, and (c) the density of the mixture. 3 2. A piston–cylinder device contains 0. 85 kg of refrigerant-134a at 10°C. The piston that is free to move has a mass of 12 kg and a diameter of 25 cm.

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The local atmospheric pressure is 88 kPa. Now, heat is transferred to refrigerant-134a until the temperature is 15°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. 3. Determine the specific volume of superheated water vapor at 10 MPa and 400°C, using (a) the ideal-gas equation, (b) the steam tables. 4. Determine the specific volume of superheated water vapor at 3. 5 MPa and 450°C based on (a) the ideal-gas equation, (b) the steam tables. 5. A 3. 7-m3 tank contains 100 kg of nitrogen at 175 K. Determine the pressure in the tank, using (a) the ideal-gas equation. Compare your results with the actual value of 1505 kPa. 6. A 1-m3 tank contains 2. 841 kg of steam at 0. 6 MPa. Determine the temperature of the steam, using (a) the idealgas equation 7. A piston–cylinder device initially contains 0. 07 m3 of nitrogen gas at 130 kPa and 120°C. The nitrogen is now expanded to a pressure of 100 kPa polytropically with a polytropic exponent whose value is equal to the specific heat ratio (called isentropic expansion).

Determine the final temperature and the boundary work done during this process. 8. A mass of 5 kg of saturated water vapor at 300 kPa is heated at constant pressure until the temperature reaches 200°C. Calculate the work done by the steam during this process. 9. A 0. 5-m3 rigid tank contains refrigerant-134a initially at 160 kPa and 40 percent quality. Heat is now transferred to the refrigerant until the pressure reaches 700 kPa. Determine (a) the mass of the refrigerant in the tank and (b) the amount of heat transferred.

Also, show the process on a P-v diagram with respect to saturation lines. 10. A well-insulated rigid tank contains 5 kg of a saturated liquid–vapor mixture of water at l00 kPa. Initially, three-quarters of the mass is in the liquid phase. An electric resistor placed in the tank is connected to a 110-V source, and a current of 8 A flows through the resistor when the switch is turned on. Determine how long it will take to vaporize all the liquid in the tank. Also, show the process on a T-v diagram with respect to saturation lines. 11.

A piston–cylinder device contains steam initially at 1 MPa, 450°C, and 2. 5 m3. Steam is allowed to cool at constant pressure until it first starts condensing. Show the process on a T-v diagram with respect to saturation lines and determine (a) the mass of the steam, (b) the final temperature, and (c) the amount of heat transfer. 12. A 3-m3 rigid tank contains hydrogen at 250 kPa and 550 K. The gas is now cooled until its temperature drops to 350 K. Determine (a) the final pressure in the tank and (b) the amount of heat transfer. 13.

A 4-m x 5-m x 6-m room is to be heated by a baseboard resistance heater. It is desired that the resistance heater be able to raise the air temperature in the room from 7 to 23°C within 15 min. Assuming no heat losses from the room and an atmospheric pressure of 100 kPa, determine the required power of the resistance heater. Assume constant specific heats at room temperature. 14. A 600-MW steam power plant, which is cooled by a nearby river, has a thermal efficiency of 40 percent. Determine the rate of heat transfer to the river water.

Will the actual heat transfer rate be higher or lower than this value? Why? 15. A steam power plant receives heat from a furnace at a rate of 280 GJ/h. Heat losses to the surrounding air from the steam as it passes through the pipes and other components are estimated to be about 8 GJ/h. If the waste heat is transferred to the cooling water at a rate of 145 GJ/h, determine (a) net power output and (b) the thermal efficiency of this power plant. 16. Solar energy stored in large bodies of water, called solar ponds, is being used to generate electricity.

If such a solar power plant has an efficiency of 4 percent and a net power output of 350 kW, determine the average value of the required solar energy collection rate, in Btu/h. 17. A household refrigerator with a COP of 1. 2 removes heat from the refrigerated space at a rate of 60 kJ/min. Determine (a) the electric power consumed by the refrigerator and (b) the rate of heat transfer to the kitchen air. 18. A household refrigerator runs one-fourth of the time and removes heat from the food compartment at an average rate of 800 kJ/h. If the COP of the refrigerator is 2. , determine the power the refrigerator draws when running. 19. Determine the COP of a heat pump that supplies energy to a house at a rate of 8000 kJ/h for each kW of electric power it draws. Also, determine the rate of energy absorption from the outdoor air. 20. Refrigerant-134a enters the condenser of a residential heat pump at 800 kPa and 35°C at a rate of 0. 018 kg/s and leaves at 800 kPa as a saturated liquid. If the compressor consumes 1. 2 kW of power, determine (a) the COP of the heat pump and (b) the rate of heat absorption from the outside air.


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