Question: Air, saturated with water vapor, at 1 atm and 77°C, flows downward along a flat, smooth plate at a velocity of 3 m/s. The plate is 30 cm high (flow direction) and 1.8 m wide. It is cooled by circulating water on its back side. The cooling water is circulated so that its average temperature is effectively 18°C over the entire back surfaces. The heat-transfer coefficient between the coolant and the back surface is estimated to be 1100W/(m2 . K).
The wall is 1.3 mm thick and has a thermal conductivity of 26W/(m· K). Estimate the total rate of condensation of water and the total heat-transfer rate to the coolant, assuming that the condensate on the plate surface runs off fast enough that its heat-transfer resistance may be neglected. Is B a constant along the surface? What are the necessary conditions for B to be a constant? Describe how you would propose to analyze the problem, taking into consideration the liquid condensate film on the plate surface.