Question

You are offered an opportunity to invest in a device that will split high pressure feed air stream (p₁ = 1.5 bar, T₁ = 30^oC) into two streams, each with ½ the molar flowrate as the inlet stream. One of these is at –150^oC and the other stream consists of hot air at 210^oC. Assume that pressure of both exit streams is 1 bar. No other input from the surroundings is required, and there is no other impact on the surroundings. Assume air is an ideal gas and has C_p = 7/2 R and C_v = 5/2 R.

Determine if this device is thermodynamically possible. Explain why or why not.

Answer 1

FOR ANY PROCESS TO BE THERMODYNMICALLY FEASIBLE, TOTAL ENTROPY CHANGE ASSOCIATED WITH IT SHOULD BE GREATER THAN OR EQUAL TO ZERO. SINCE CALCULATED TOTAL ENTROPY CHANGE IS LESS THAN ZERO THEREFORE PROCESS IS NOT THERMODYNAMICALLY POSSIBLE.

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