Notes_10_Control_Volume_Mass_Conservation0

Notes_10_Control_Volume_Mass_Conservation0 - Meeting...

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1 Meeting 10--Section 5-1
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Announcements Exam 1 Monday June 27th. 10 AM. Zach 104B. Chapters 1 – 4. Same format as previous semester exams posted on e-learning. Make sure to work the current HW 10. 2
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What we covered Monday Examples of First Law analysis for closed systems. Specific Heats. 3
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Example: 4-73 Argon is compressed in a polytropic process with n = 1.2 from 120 kPa and 10 ºC to 800 kPa in a piston-cylinder device. Determine the work produced and heat transferred during this compression process, in kJ/kg. 4
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5 Argon is compressed in a polytropic process. The work done and the heat transfer are to be determined. Assumptions 1 Argon is an ideal gas since it is at a high temperature and low pressure relative to its critical point values of 151 K and 4.86 MPa. 2 The kinetic and potential energy changes are negligible, 0 pe ke 2245 2245 . Properties The properties of argon are R = 0.2081kJ/kg K and c v = 0.3122 kJ/kg K (Table A-2 a ). Analysis We take argon as the system. This is a closed system since no mass crosses the boundaries of the system. The energy balance for this system can be expressed as ) ( 1 2 out , in energies etc. potential, kinetic, internal, in Change system mass and work, heat, by nsfer energy tra Net out in T T mc U W Q E E E b - = = - = - v        Using the boundary work relation for the polytropic process of an ideal gas gives kJ/kg 109.5 1 120 800 1.2 - 1 K) 283 )( K kJ/kg 2081 . 0 ( 1 1 2 . 1 / 2 . 0 / ) 1 ( 1 2 1 out , - = - = - - = - n n b P P n RT w Thus, kJ/kg 109.5 = in , b w The temperature at the final state is K .2 388 kPa 120 kPa 800 K) 283 ( 2 . 1 / 2 . 0 1 ( 1 2 1 2 = = = )/n n- P P T T From the energy balance equation, kJ/kg 6 . 76 K ) 283 K)(388.2 kJ/kg 3122 . 0 ( kJ/kg 5 . 109 ) ( 1 2 out , in - = - + - = - + = T T c w q b v Thus, kJ/kg 76.6 = out q Q Argon 120 kPa 10°C P v n = constant
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Teamplay: Problem 4-81 Air is contained in a cylinder device fitted with a piston-cylinder. The piston initially rests on a set of stops, and a pressure of 300 kPa is required to move the piston. Initially, the air is at 100 kPa and 27 ºC and occupies a
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This note was uploaded on 10/04/2011 for the course MEEN 315 taught by Professor Ramussen during the Summer '07 term at Texas A&M.

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Notes_10_Control_Volume_Mass_Conservation0 - Meeting...

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