2008_midsem - QQ INDIAN INSTITUE OF TECHNOLOGY 4 Date FN/AN...

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Unformatted text preview: QQ INDIAN INSTITUE OF TECHNOLOGY 4 Date' ............... FN/AN Time: 2 hours Full Marks: 60 ; No. of StL-Zdentsz‘" 215 Spring Mid-Semester Examination, 2008 Mechanical Engineering Subject No.: ME22002 2nd Year B.Tech (H) Subject Name: Thermodynamics Answer all the questions. Marks for the questions are shown on the margin. Use steam tables (supplied with the Question Paper) as and when necessary. 1. Employing first and second law of thermodynamics show that a compressor, operating between given inlet and exit states, consumes the least amount of power when it is compressing in a reversible manner while exchanging heat with the surroundings. [7] 2. Two rigid tanks each contain 10 kg N2 gas (assume N2 as an ideal gas with constant specific heats) at 1000 K, 500 kPa. They are thermally connected to a reversible heat pump (as shown in . the figure below), which heats one and cools the other in a reversible manner with no heat transfer to the surrounding. In this process, one tank gets heated to 1500 K and the process stops. Find the final temperature in the other tank and final pressure in both the tanks. [5+3] W Heat Pump 3. A balloon initially contains 65 m3 of Helium gas at atmospheric conditions of 100 kPa and 22°C. It is connected by a valve to a large reservoir which supplies helium gas at 150 kPa and ‘ 25°C. Now the valve is opened and the gas is allowed into the balloon until pressure equilibrium . with the large reservoir is achieved. The filling process is such that the volume increases linearly with pressure. .lgnore kinetic and potential energy effects. Treat helium as an ideal gas having R = 2.077 kJ/kg K, c9: 5.19 kJ/kg K, cv= 3.116 kJ/kg K. a. If no heat transfer takes place during the process, determine the final temperature inside the balloon. b. If the work done due to the stretching of the material of the balloon is also considered in the analysis, how is it going to affect the final temperature in the balloon? Discuss qualitatively only. [12+3] 4. In a power plant, feedwater is heated by steam extracted from; the turbine in a heat ' exchanger as shown in the figure. Steam enters the heat exchanger a]: 10 bar and 200°C and ' leaves as saturated liquid at the same pressure. Feedwater enters the heat exchanger at 25 bar and 50°C and leaves at 170°C which is about ' 10°C below the exit temperature of the CD . . . Steam ‘ steam. Neglect changes in /kinetic and from + potential energy terms and assume a steady “Hume . . gamma! flow system. Neglecting any heat transfer +® with the ambient, determine: a. the ratio of the mass flow rates of the extracted steam and the feedwater b. total entropy generation for this process per unit mass flow rate of I ' . + feedwater. c. if the heat exchanger experiences heat . sathamd loss to the ambient, how would that affect the answer in part (b). Only a qualitative explanation is required. [5+7+3] 5. A mass of 5 kg of saturated liquid-vapour mixture of water is contained in a piston-cylinder device at 1.2 bar. Initially, 2 kg of the water is in liquid phase and the rest is in vapour phase. Heat is now transferred to the water, and the piston, which is resting on a set of stops, starts moving when the pressure inside reaches 3 bar. Heat transfer continues until the total volume increases by 20 percent. Show the process on a P—v diagram. Determine: (a) the initial and final temperatures (b) the mass of liquid water when the piston first starts moving, and (c) the work done during this process. - [2+5+2+§J End of Paper ...
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