MONO- AND MULTI-COMPONENT DROPLET COOLING/HEATING AND EVAPORATION: COMPARATIVE ANALYSIS OF NUMERICAL MODELS

The results of a comparative analysis of the predictions of various models for mono- and multi-component droplet cooling/heating and evaporation in ambient air are presented. The finite thermal conductivity and species diffusivity inside droplets are taken into account along with the effects of recirculation inside droplets. The effect of the deviation from the Raoult law (non-ideal mixtures) is taken into account. It is pointed out that the predictions of the models based on the analytical and numerical solutions to the heat transfer and species diffusion equations inside droplets (the location of the droplet surface was fixed during the timestep in both models) are almost identical for the one-way solution, which gives confidence in both solutions. At the initial stage of droplet cooling/heating and evaporation, the coupled solution predicts visibly lower droplet temperatures, compared with the predictions of the one-way solution. At the later stage of droplet cooling/heating and evaporation, the coupled solution predicts higher droplet temperatures, compared with the predictions of the one-way solution. At the initial stage of droplet evaporation, the predictions of the models, taking and not taking into account the effects of the moving boundary during the timesteps on the solutions to the heat transfer and species diffusion equations, are very close. At the same time, the difference in the predictions of these models needs to be taken into account when the whole period of droplet evaporation up to the complete evaporation of droplets is considered. The effect of the moving boundary is shown to be much stronger for the solution to the species diffusion equations than for the solution to the heat conduction equation. The effect of the choice of the approximation of the binary diffusion coefficient for the ethanol/acetone mixture in air is shown to be small and can be ignored in most engineering applications. The modeling results are compared with experimental observations of acetone/ethanol mono- and multi-component droplet cooling/heating and evaporation where appropriate.