1. A heat exchanger brings 10 kg/s water from 100?C up to 500?C at 2000 kPa using air coming in at 1400 K and leaving at 460 K. What is the second law efficiency?
2. Calculate the second-law efficiency of the counter- flowing heat exchanger in Problem 7.105 with an ambient at 20?C.
Problem 7.105
A counter flowing heat exchanger has one line with 2 kg/s at 125 kPa, 1000 K entering, and the air is leaving at 100 kPa, 400 K. The other line has 0.5 kg/s water coming in at 200 kPa, 20?C and leaving at 200 kPa. What is the exit temperature of the water and the total rate of entropy generation?
