Nonisothermal Droplet Growth in the Free Molecular Regime

The growth rates of nonane and D2O nanodroplets produced in supersonic expansions are characterized using small angle X-ray scattering (SAXS) and pressure trace measurements (PTM). The experimental growth rates are compared to the predictions of a Hertz–Knudsen model that assumes either isothermal or nonisothermal droplet growth in the free molecular regime. For nonane, the predicted growth rates are insensitive to both droplet temperature and the evaporation coefficient, and agree well with the experimentally measured growth rates assuming a condensation coefficient of 1. For D2O, droplet growth rates are quite sensitive to droplet temperature, and the best agreement between experiments and theory are achieved for a condensation coefficient of 1 and an evaporation coefficient in the range from 0.5 to 1. Under our experimental conditions, incorporating coagulation is important to match the measured D2O growth rates but not those of nonane.Copyright 2013 American Association for Aerosol Research