Heating and evaporation of a two-component droplet: hydrodynamic and kinetic models

A previously developed kinetic model for two-component vapour and background gas (air) is applied to the analysis of droplet heating and evaporation in Diesel engine-like conditions. The model used in the analysis is based on the introduction of the kinetic region in the immediate vicinity of the droplets and the hydrodynamic region. The presence of two components in the vapour, finite thermal conductivity and finite species diffusivity in droplets are taken into account. It is pointed out that for parameters which are typical of Diesel engine-like conditions, the heat flux in the kinetic region is a linear function of the temperature at the outer boundary of this region, but is almost independent of the density of the components at this boundary. Mass fluxes of both components in the kinetic region are shown to decrease almost linearly with increasing vapour density at the outer boundary of this region, but are almost independent of the temperature drop in the kinetic region. The model is tested for the analysis of heating and evaporation of a droplet with initial radius and temperature equal to 5 μm and 300 K, respectively, immersed into gas with temperatures 1000 K and 700 K for several mixtures of n-dodecane and p-dipropylbenzene. It is pointed out that an increase in the mass fraction of p-dipropylbenzene and kinetic effects lead to an increase in the predicted droplet evaporation time. The kinetic effects ∗Corresponding author. Tel. +44(0)1273642677; fax +44(0)1273642330; e-mail [email protected] Preprint submitted to International J Heat and Mass Transfer June 25, 2014 are shown to increase with increasing gas temperature and molar fraction of p-dipropylbenzene.