A stream of air flows steadily through a device, entering at temperature T1 and exiting at T2. The air pressure remains approximately constant. The device interacts with the atmosphere which is at temperature To and no work is produced. Although the device could be a heat exchanger, we are interested in finding the minimum possible T2. Therefore, treat the process in the device as reversible and find T2 as a function of T1 and To (for T1>To).