Question

Air undergoes a polytropic process in a piston–cylinder assembly from p₁ = 1 bar, T₁ = 295 K to p₂ = 9 bar. The air is modeled as an ideal gas and kinetic and potential energy effects are negligible.

For a polytropic exponent of 1.2, determine the work and heat transfer, each in kJ per kg of air,
(1) assuming constant c_v evaluated at 300 K.
(2) assuming variable specific heats.

W/m = -187.211 kJ/kg

Q/m= -93.563 kJ/kG

Determine the heat transfer, in kJ per kg of air, assuming variable specific heats.

Answer 1

In this problem, we simply apply the ideal gas equation for the polytropic process to calculate the work and then the heat required at constant specific heat and variable specific heat.

for constant specific heat, we use specific heat at constant volume at 300K to calculate internal energy for its application in first law.

for variable heat we directly calculate the inernal energy by properties table and then apply the first law.

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