On the Importance of Kinetic Effects in the Modelling of Droplet Evaporation at High Pressure and Temperature Conditions

Abstract

This work analyses whether the inclusion of interfacial temperature jumps is necessary in the modelling of droplet evaporation at high pressure. The analysis is divided into two parts. First, we revise the major findings from theoretical models and molecular dynamics simulations on the conditions leading to the inception of interfacial jumps and the main parameters affecting them. Second, an evaporation model is considered that includes a diffuse transition layer (Knudsen layer), in the order of a few mean free paths around the droplet, where transport processes are described by kinetic molecular theory. The analysis shows that discontinuities in temperature and chemical potential across the interface are important when molecular collisions control transport processes and result in large heat and mass fluxes. This may occur not only at low pressures, but also at high pressures and temperatures for conditions sufficiently far from global thermodynamic equilibrium and/or for sufficiently small droplets. On a macroscopic scale, the resulting correction to the boundary conditions for classical diffusion-controlled models may be significant at high evaporation rates.