which is apparently same as Eq.( ). As stated earlier, the air temperature T 1 is ruled by the thermodynamics of expansion, whereas the droplet surface temperature T L is dependent on heat transfer on droplet surface. The heat transfer consists of three process : 1) Heat conduction due to the temperature difference between T L and T 1 , 2) Release of heat by condensation, and absorption of heat by evaporation, 3) Heat transfer corresponding to temperature variation of droplets. Using the boundary layer theory [10], the temperature gradient in the vicinity of droplet surface is (T 1 -T L )/r. Therefore, the rate of heat transfer toward the surface of a droplet due to the first process is given by