Hygroscopic growth and evaporation in an aerosol with boundary heat and mass transfer

This study demonstrates an experimental method for using temperature measurements as a means for validating computations of particle size distribution in a growing or evaporating high-concentration aerosol flowing in a tube with wall heat and mass transfer. The method is based on the premise that aggregate growth or condensation from an ensemble of aerosol droplets can be inferred by comparing temperature evolution of an aerosol-laden and aerosol-free flow through a heated or cooled tube. The difference in bulk temperature is used as an indicator of latent heat effect which is directly related to condensational and evaporative particle size changes. Dimensional analysis is used to derive the conditions under which such an approach can be used. Two parameters, the “coupling number” and the dimensionless mass concentration are found to govern the sensitivity of continuous phase temperature to aggregate evaporation or condensation of the droplet ensemble, and the sensitivity of temperature to droplet diameter changes, respectively. Experimental data for an aqueous saline aerosol flowing through a heated, constant wall temperature tube are presented and compared to predictions derived using a Lagrangian plug-flow model with a fully moving particle bin structure. Measured and predicted bulk phase temperatures agree to within 3%. Using sensitivity analysis, it is shown that hygroscopic particle diameter changes will be at least as accurate.