Download Heat Transfer Rate - Thermodynamics - Homework and more Exercises Thermodynamics in PDF only on Docsity! Homework Problems 1 A classroom that normally contains 40 people is to be air conditioned with window air conditioning units of 6 kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360 kJ/h. There are 10 light bulbs in the room, each with a rating of 100 W. The rate of heat transfer to the classroom through the walls is 15,000 kJ/h. If the room air is to be maintained at a constant temperature of 21oC, determine the number of air-conditioning units required. 2 A 0.5 m3 rigid tank contains regrigerant-134a initially at 160 kPa and 40% quality. Heat is now transferred to the refrigerant until the pressure reaches 700 kPa. Determine (a) the mass of refrigerant in the tank and (b) the amount of heat transferred. Also, show the process on a P-v diagram with respect to the saturation lines. 3 A 20 ft3 rigid tank contains saturated regrigerant-134a vapor at 160 psia. As a result of heat transfer from the refrigerant, the pressure drops to 50 psia. Show the process on a P-v diagram with respect to the saturation lines, and determine (a) the final temperature, (b) the amount of refrigerant that has condensed, and (c) the heat transfer. 4 An insulated piston-cylinder device contains 5 L of saturated liquid water at a constant pressure of 175 kPa. Water is stirred by a paddle wheel while a current of 8 A flows for 45 min through a resistor placed in the water. If one half of the liquid is evaporated during this constant-pressure process and the paddle-wheel work amounts to 400 kJ, determine the voltage of the source. Also, show the process on a P-v diagram with respect to the saturation lines. 5 A piston-cylinder device initially contains steam at 200 kPa, 200oC, and 0.5 m3. At this state a linear spring (F x) is touching the piston but exerts no force on it. Heat is now slowly transferred to the steam causing the pressure and the volume to rise to 500 kPa and 0.6 m3, respectively. Show the process on a P-v diagram with respect to the saturation lines and determine (a) the final temperature, (b) the work done by the steam, and (c) the total heat transferred. 6 A piston-cylinder device initially contains 0.8 m3 of saturated water vapor at 250 kPa. At this state, the piston is resting on a set of stops and the mass of the piston is such that a pressure of 300 kPa is required to move it. Heat is now slowly transferred to the steam until the volume doubles. Show the process on a P-V diagram with respect to saturation lines and determine (a) the final temperature, (b) the work done during this process, and (c) the total heat transfer. docsity.com
