Dry air at 35°C and a velocity of 15 m/s flows over a long cylinder of 20-mm diameter, the cylinder is covered with a thin porous coating saturated with water, and an imbedded electrical heater supplies power to maintain the coating surface temperature at 20°C.

(a) What is the evaporation rate of water from the cylinder per unit length (kg/h ∙ m)? What electrical power per unit length of the cylinder (W/m) is required to maintain steady-state conditions?

(b) After a long period of operation, all the water is evaporated from the coating and its surface is dry. For the same free stream conditions and heater power of part (a), estimate the temperature of the surface.