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lecture_12.20080921.48d6fd07111b11.45140595

# lecture_12.20080921.48d6fd07111b11.45140595 - Lecture 12...

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Lecture 12 Properties 9/22/08

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Problem 3.116 A piston-cylinder assembly contains air at a pressure of 30 lbf/in 2 . and a volume of 0.75 ft 3 . The air is heated at constant pressure until its volume is doubled. Assuming the ideal gas behavior with constant specific heat ratio = k = 1.4, determine the work and heat transfer. c p = c v + R; c p / c v = k; c v k = c v + R; hence c v = R/(k-1) c v /R = 1/(k-1) = 1/0.4 = 2.5 pV = mRT; Work = p(V 2 -V 1 ) = 30x144 x (1.5 – 0.75) = 3240 ft. lbf Change in internal energy = c v (T 2 – T 1 ) = c v (pV 2 /R – pV 1 /R) = (c )(p)(V -V )/R = (30 x 144) (0.75) (1/0.4) =
Problem 3.123 Air is confined to one side of a rigid container divided by a partition as shown in Fig. 3.123. The other side is initially evacuated. The air is initially at p 1 = 5 bar. T 1 = 500K, V 1 = 0.2 m 3 . When the partition is removed, the air expands to fill the entire chamber. Measurements show that V 2 = 2 V 1 , p 2 = p 1 /4. Assuming that air behaves as an ideal gas, determine the final temperature and the heat transfer in kJ.

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lecture_12.20080921.48d6fd07111b11.45140595 - Lecture 12...

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