1947 Volume 25 Issue 1-3 Pages 1-11
The author intended to get a formula expressing the rate of evaporation of falling rain drops theoretically. Applying the theory of boundary layer on the falling rain drop we obtained a formula for the evaporation from the region between the forward point (i.e. stagnant point dynamically, point A in Fig. 2) and the separation point (point B in Fig. 2) of the drop: viz. where k: diffusion coef. of the water vapour through air, a: radius of the drop; R: Raynolds no. of the drop for the rate of fall; Co, C_??_: water vapour density (g/cm3) on the surface of the drop and in the air respectively.
The flow in the wake of the drop is so complicated that we could not get the rate of evaporation from this region. So comparing with Fr_??_ssling's experimental formula we gave the formula M=0.233×4πka_??_R(Co-C_??_) for the rate of evaporation of falling rain drops. Comparing this with the result for cloud and fog particles which was obtained by the present author (Studies on Evaporation II and III) the rate of evaporation of water drops in the case of Co-C_??_=1 was illustrated diagrammatically in Fig. 4.