Consider the two-stage air compressor with inter-stage cooling described in Problem 3.23. For this thermal system determine the following,

a. The exergy destruction rate in each component (kW)

b. The exergetic efficiency of each component.
The dead state can be considered as atmospheric conditions; 1 atm, 25°C.

Problem 3.23

A two-stage air compressor with inter-stage cooling is shown in Figure P3.23. The dry air enters the first compressor stage at 1 atm, 25°C, a volumetric flow rate of 3500 cfm, and is compressed to 5 bar. The air then passes through a heat exchanger with no appreciable drop in pressure, after which, it is compressed in the second stage to 10 bar. The isentropic efficiency of both compression stages is 83%. The heat exchanger is a counter flow heat exchanger where the air is being cooled by water. The water enters the heat exchanger at 20°C and exits at 75°C. The pinch point temperature difference of the heat exchanger is 4 K and the pinch point occurs on the cold end.

Transcribed Image Text:

1 T = 75C Compressor 1 6 2+ P =5 bar P = 1 atm -T = 25C ATHX = 4 K www www = 3500 cfm nct=7=0.83 FIGURE P3.23 Two-stage air compressor with inter-stage cooling. Cooling water 5+ T = 25C Pinch point 3 P = P Compressor 2 + P = 10 bar