Air at 1200 kPa and 250°C fills a balloon with a volume of 2.85 m3. The balloon cools and expands until the pressure is 400 kPa. The pressure and volume follow a relationship given by PV1.3 = constant. Determine the work done by the air as it expands, and the final temperature of the air.
Given: P1 = 1200 kPa; T1 = 250°C = 523 K; V1 = 2.85 m3; P2 = 400 kPa; PV1.3 = constant
What will be an ideal response?
From the ideal gas law, m = P1V1/RT1
For air, R = 0.287 kJ/kg-K, so m = 22.78 kg
The moving boundary work for a polytropic process with n ? 1:
From the ideal gas law:
T2 = P2V2/mR = 406 K = 133oC
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