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Unformatted text preview: Chapter 4 # 65E o A rigid tank contains 20lbm of air at 50 psia and 80°F. The air is now heated until its pressure doubles. Determine (a) the volume of the tank and (b) the amount of heat transfer Closed system Substance: Assuming that air acts as an ideal gas Process: constant volume First law for a stationary system • (Q in – Q out ) + (w in – w out ) • Q net,in – w net,out = mΔu • w b = ∫pdv = 0 o shaft work = 0 no shaft o electrical work = 0 no electrical connections Q in = mΔu Q in = mc v ΔT p 2 v 2 /T 2 = p 1 v 1 /T 1 p 2 /T 2 = p 1 /T 1 2p 1 /T 2 = p 1 /T 1 T 2 = 1080 R = 620°F Q in = mΔu Q in = mc v ΔT Q in = 20 lbm (.175) (540 btu/lbm) Q in = 1890 AIR TABLE • At 80 = 540 R u 1 = 92.04 • At 1080R u 2 = 186.93 • Δu = 94.89 • ΔU = mΔu = 1897.8 Btu • Q = Δu = 1897.8 Btu o pV = mRT...
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 Fall '08
 knisley
 Heat Transfer, blah blah blah, Qin, Assume constant cp, electrical connections Qin

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