Applying the Exergy Balance: Closed Systems As shown in Fig. P7.48,...

Applying the Exergy Balance: Closed Systems

As shown in Fig. P7.48, one-half pound of nitrogen (N₂), in a piston–cylinder assembly, initially at 80^oF, 20 lbf/in.², is compressed isothermally to a final pressure of 100 lbf/in.² During compression, the nitrogen rejects energy by heat transfer through the cylinder’s end wall, which has inner and outer temperatures of 80^oF and 70^oF, respectively.

(a) For the nitrogen as the system, evaluate the work, heat transfer, exergy transfers accompanying work and heat transfer, and amount of exergy destruction, each in Btu.

(b) Evaluate the amount of exergy destruction, in Btu, for an enlarged system that includes the nitrogen and the wall, assuming the state of the wall remains unchanged. Comment.

Use the ideal gas model for the nitrogen and let T₀ = 70^oF, p₀ = 14.7 lbf/in.²