Evaporation of stationary droplets in high temperature surroundings

An experimental study of the rate of evaporation of stationary droplets of water, methanol, cumene, pentane and benzene was carried out in an electrically‐heated 9‐inch stainless steel sphere. The gaseous environment consisted of the superheated vapor of the liquid under investigation and, in all cases, the wall and gas temperatures were the same. Drop diameters ranged from 0.4 to 1.4 mm., and temperatures from 100°C. to 550°C. The evaporation rate of stationary droplets in high temperature surroundings does not appear to be governed by the rate of heat transfer by natural convection, since no dependency of the Nusselt Number on the Grashof Number was found. Attempts to correlate the results on the basis of Godsave's model (conduction across the boundary layer controlling) or Spalding's modified approach to the latter were equally unsuccessful. The experimental evaporation rates could, however, be very satisfactorily correlated in terms of Spalding's Transfer Number B. The correlation obtained indicates that the mechanism of the evaporation process is governed by the effect of the evolved vapors on the boundary layer flow.