Levitation Diffusion Chamber Measurements of the Mass Growth of Small Ice Crystals from Vapor

Abstract

levitation diffusion chamber designed to examine the mass growth from the vapor of small ice particles (diameter < 100 ?m) at ambient pressure (?970 hPa) and low temperature (T < ?30°C) is presented. The diffusion chamber is unique in that charged ice particles are levitated by an opposing voltage on the lower copper plate with lateral stability provided by button quadrupole electrodes attached to the upper copper plate. The button electrodes are far from the ice particle growth region, allowing ice particles to grow free of substrate influences. Experiments have been conducted for temperatures from ?30° to ?35.7°C, ice supersaturations from 2.5% to 28.6%, and over growth times ranging from 5 to 15 min. The experiments indicate that mass varies nonlinearly in time and exhibits a dependence on initial particle radius and ice supersaturation in accord with expectations from theory. In contrast to expectations from spherical capacitance theory, the derived mass growth rates do not scale linearly with radius, and derived effective shape factors (capacitance normalized with radius) are approximately 0.5. Fitting the growth data with a theoretical model indicates that growth is limited by surface kinetics with deposition coefficients ranging from 0.003 to 0.02.