Transient Stefan flow and thermophoresis around an evaporating droplet

The transient transfer of mass and heat from an evaporating supercooled water droplet is investigated theoretically, and the results of numerical computations are applied to the scavenging of atmospheric particles by vapor-grown ice particles falling from mixed clouds. The problem is simplified to a classical heat-transfer problem, and the relative velocities of Stefan flow away from the supercooled droplets and the opposing thermophoresis are determined for a range of droplet radii and time intervals (from the onset of evaporation). The thermophoresis effect is found to be practically negligible for droplets of radius 8 microns or more during the 10-100-microsec residence of a supercooled droplet in the vicinity of an ice crystal. The Stefan-flow/Brownian-motion model of particle scavenging proposed by Vittori and Prodi (1967) is thus supported.