A co-flowing heat exchanger receives air at 800K and 15 MPa and water at 15C and 100 kPa. The two flows exchange energy as they flow alongside each other to the exit, where the air should be cooled to 350K. Investigate the range of water flows necessary per kilogram per second of air flow and the possible water exit temperatures, with the restriction that the minimum temperature difference between the water and air should be 25C. Include an estimation for the overall entropy generation in the process per kilogram of air flow.