HW2 - (b Determine whether this cycle is a power cycle or...

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Department of Mechanical Science and Engineering ME 300 Thermodynamics Section D Fall 2010 Homework #2 due Friday, September 10 th Problem 2.1 Complete each line of the table below by applying the first law of thermodynamics (conservation of energy principle) for a closed system. Q W U 1 U 2 m u 2 -u 1 kJ kJ kJ kJ kg kJ/kg 180 850 750 2 250 -150 325 5 400 150 2 -150 -300 750 950 4 -150 200 650 100 Problem 2.2* A piston-cylinder device initially contains 0.1 m 3 of air at 400 kPa and 20 C. The piston is allowed to move slowly until the pressure inside the piston is 100 kPa. The temperature inside the cylinder remains constant (this is called an isothermal expansion). The relationship between pressure and volume is given as p · V = constant . (a) Calculate the final volume, in m 3 . (b) Calculate the work for this process, in kJ. Is the work done by the system or on the system? Problem 2.3 A closed system undergoes a thermodynamic cycle consisting of four processes. Process Δ U Δ KE Δ PE Δ E Q W kJ kJ kJ kJ kJ kJ 1-2 30 -10 -10 0 2-3 80 5 0 100 3-4 0 10 -60 60 4-1 -40 0 -35 0 (a) Determine the missing entries in the above table.
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Unformatted text preview: (b) Determine whether this cycle is a power cycle or refrigeration cycle. Determine the thermal efficiency. Problem 2.4* A gas within a piston-cylinder assembly undergoes a thermodynamic cycle consisting of three processes: Process 1-2: Constant Volume, V=0.01m 3 , U 2-U 1 = 25 kJ Process 2-3: Expansion with pV 1 . 2 = constant , U 2 = U 3 Process 3-1: Constant pressure, p=3.5 bar, W 31 =-25kJ The changes in kinetic and potential energy can be neglected for this process. (a) Sketch the cycle on a p-V diagram. (b) Calculate the net work of the cycle, in kJ. (c) Calculate the heat transfer for process 2-3, in kJ. (d) Calculate the heat transfer for process 3-1, in kJ. (e) Is this a power or refrigeration cycle? Problem 2.29 from the textbook* For problems marked with * you need to use the Five Step methodology as outline in the homework policy. 1...
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