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An insulated cylinder fitted with a piston contains R-12 at 25°C with a quality of 90% and V=45 L. The piston moves and the R-12 expands until it exists as saturated vapour. During this, R-12 does 7kJ of work against the piston. Determine the final temperature, assuming that the process is adiabatic.

An insulated cylinder fitted with a piston contains R-12 at 25°C with a quality of 90% and V=45 L. The piston moves and the R-12 expands until it exists as saturated vapour. During this, R-12 does 7kJ of work against the piston. Determine the final temperature, assuming that the process is adiabatic. Correct Answer -15°C

Energy Eq.: m(u2 − u1) = 1Q2 – 1W2 State 1: (T, x) => v1 = 0.000763 + 0.9 × 0.02609 = 0.024244 m3/kg m = V1/v1 = 0.045/0.024244 = 1.856 kg and u1 = 59.21 + 0.9 × 121.03 = 168.137 kJ/kg Q = 0 = m(u2 – u1) + 1W2 = 1.856 × (u2 – 168.137) + 7.0 => u2 = 164.365 kJ/kg = ug at T2 and T2 comes out to be -15°C.

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