Question: At a particular region in a steam condenser the fluid is a mixture of 80 percent steam (by mass) and 20 percent air. The total pressure is 6.75 kPa, and the temperature is that of saturated steam at that pressure. What is the necessary condition at the surface of the tubes for condensation to take place? In simple condensation the resistance to heat transfer is usually considered to be entirely that of the liquid film that forms on the surface. How does the present problem differ? Suppose the liquid filin has an average thickness of 0.1 mm; investigate the, effect of the air on the overall resistance to heat transfer between the tube metal surfaces and the free-stream mixture.