Question #173964

Note: Draw the P-V, T-S diagrams for all problems

13. The work required to compress a gas reversibly according to PV 1.3 =C is 68KJ. if there is no flow

determine the change in internal energy, enthalpy and heat if the gas is CO 2 .

14. Air is compressed polytropically so that the quantity PV 1.4 is constant. If 0.02 m 3 of air at atmospheric pressure of 101.3 KPA and 4C are compressed to a gage pressure of 405KPAg, determine the final temperature of air in C.

Expert's answer

13. pV^{1.3} = C

Q = 0

∆U = Q - W = -W

∆H = ∆U = -68 000 J

14. pV^{1.4} = const

V_{1} = 0.02 m^{3}; p_{1} = 101.3 kPa; T_{1} = 4°C = 4 + 273 = 277 K;

p_{2} = 101.3 + 405 = 506.3 kPa

p_{1}V_{1}^{n} = p_{2}V_{2}^{n}

p_{1}/p_{2} = (V_{2}/V_{1})^{n}

101.3/506.3 = (V_{2}/0.02)^{1.4}

V_{2} = 0.006 m^{3}

Substance is ideal gas pV = RT

T = pV/R = 506.3 x 10^{3} Pa x 0.006 m^{3} / 8.31 m^{3 }Pa K^{-1} = 365 K

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