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A cylinder/piston contains air at 100 kPa and 20°C with a V=0.3 m^3. The air is compressed to 800 kPa in a reversible polytropic process with n = 1.2, after which it is expanded back to 100 kPa in a reversible adiabatic process. Find the net work.

A cylinder/piston contains air at 100 kPa and 20°C with a V=0.3 m^3. The air is compressed to 800 kPa in a reversible polytropic process with n = 1.2, after which it is expanded back to 100 kPa in a reversible adiabatic process. Find the net work. Correct Answer -174.6 kJ/kg

m = P1V1/RT1 = (100 × 0.3)/(0.287 × 293.2) = 0.3565 kg T2/T1 = (P2/P1)^ = 293.2(800/100)^(0.167) = 414.9 K W = (P2 v2 – P1 v1)/(1-n) = R(T2-T1)/(1-n) = 0.287(414.9-293.2)/(1-1.20) = -174.6 kJ/kg.

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