Mathematical simulation for non-equilibrium droplet evaporation

Investigations of acute problems of phase transitions in continua mechanics need adequate modeling of evaporation, which is extremely important for the curved surfaces in the presence of strong heat and mass diffusion fluxes. Working cycle of heat pipes is governed by the active fluid evaporation rate. Combustion of most widely spread hydrocarbon fuels takes place in a gas-phase regime. Thus, evaporation of fuel from the surface of droplets turns to be one of the limiting factors of the process as well. In the present paper processes of non-equilibrium evaporation of small droplets in a quiescent air and in streaming gas flows were investigated theoretically. The rate of droplet evaporation is characterized by a dimensionless Peclet number (Pe). A new dimensionless parameter I   characterizing the deviation of phase transition from the equilibrium was introduced, which made it possible to investigate its influence on variations of the Peclet number and to determine the range of applicability for the quasi-equilibrium model. As it follows from the present investigations accounting for non-equilibrium effects in evaporation for many types of widely used liquids is crucial for droplets diameters less than 100μm, while the surface tension effects essentially manifest only for droplets below 0.1μm. The effects of velocity non-equilibrium and droplet atomization were taken into account.