Air is compressed from 1 bar, 27C, to 3.5 bars, 127C, in a steady-flow device. A

Question

Air is compressed from 1 bar, 27C, to 3.5 bars, 127C, in a steady-flow device. Any heat transfer occurs between the air and the environment at 27C, and actual shaft work input is 170.0 kJ/kg (Assuming constant specific heats, and list your assumptions). Use the ideal gas model for air. a. Determine the heat transfer, in kJ/kg, for the air flowing through the compressor. b. Determine the entropy generation, in kJ/(Kg.K), for the control volume which includes the air flow and the immediate surroundings where heat transfer occurs.

Explanation / Answer

a) ideal work done = Cp.dT = 1.005 x (127 - 27) = 100.5 KJ/Kg

heat transfer = 170 - 100.5 = 69.5 KJ/Kg

b) entropy generated = Q/T

here T = 27 C = 300 K

S = 69.5/300 = 0.23 KJ/Kg.K

c)

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