Water is to be cooled by passing through the tube in an insulated cross-flow heat exchanger, while air flows over the outside surface of the tube. The water enters the 4.0-cm-diameter pipe with a velocity of 15 m/s, a temperature of 150°C, and a quality of 0.10. The water exits as a liquid at 100°C (This can be approximated as a saturated liquid at 100°C.) The air enters the heat exchanger at 15°C.

a. For a mass flow rate of the air of 5.0 kg/s, determine the air exit temperature. You may use specific heats for calculating the enthalpy changes of air. (neglect the differences in potential and kinetic energies).
b. Using your heat exchanger model to acquire the data, plot the exit temperature of the air as the air mass flow rate varies from 4.0 kg/s to 25 kg/s.