Question 1

You find an interesting expression for entropy generation during an irreversible compression in terms of efficiency (η), the ratio of pressures, and γ. The expression is valid for ideal gases with constant, temperature independent, 

• For rp = 5, plot Sgen for an ideal monoatomic, diatomic, and polyatomic gas versus efficiency (0.5 ≤ η ≤ 1). You can draw a rough sketch of your plot in your answers. At a given efficiency, which gas has the lowest entropy generated?
• Simply by observing the terms in the equation for Sgen, can you rationalize which monoatomic, diatomic, or polyatomic gases will have the lowest entropy generation at a given efficiency and rp? Explain in 2-4 sentences.
• An adiabatic compressor having efficiency η, operates at a steady state between an inlet condition of T1, P1, and an outlet condition of P2. Derive the relationship between Sgen (entropy generated) and η shown above. The fluid behaves like an ideal gas with temperature-independent heat capacities Cp, and Cv.