Influence of ambient vapor concentration on droplet evaporation in a perspective of comparison between diffusion controlled model and kinetic model

Abstract

A comparative study of purely diffusion controlled, kinetic, and empirical models has been executed on the predictions of evaporation characteristics of water droplet in a quiescent ambience of air with varying vapor concentrations at different pressures and temperatures. A significant increase in droplet lifetime with free stream vapor concentration has been observed at lower values of the free stream temperature, as predicted by all the models. An increase in ambient pressure increases the droplet lifetime at low temperature, while it does the opposite at higher ambient temperature. The droplet lifetime predicted by the kinetic model is always greater than that predicted by the purely diffusion controlled model. For a droplet of initial radius 20 μm, the purely diffusion controlled and kinetic models underpredict the droplet lifetime as compared to that obtained from the empirical model. For a droplet of initial radius of 5 μm, the purely diffusion controlled model underpredicts the droplet lifetime while the kinetic model overpredicts the same as compared to empirical values. The predictions of lifetime by kinetic models are closer to those obtained from empirical ones in case of evaporation in vapor rich ambience.