The non-ideal evaporation behaviors of ethanol/heptane droplets: Impact on diameter, temperature evolution and the light scattering by droplet at the rainbow angle

This paper aims to investigate the influence of non-ideal vapor-liquid equilibrium (VLE) on the heating and evaporation of ethanol/heptane binary droplets. Three correction parameters, the activity coefficient, the Poynting factor, and the fugacity coefficient, are incorporated in the Effective Thermal Conductivity Model (ECM) and Effective Diffusivity Model (EDM) to present the non-ideal behavior at droplet surface. Rainbow theory was used to present the difference between the ideal and non-ideal models by predicting the scattering light patterns with the obtained results. The evaporation process of ethanol/heptane droplet was performed by the ideal and non-ideal VLE methods, with the ambient temperature varying from 473 K to 673 K, ambient pressure of 1 and 10 bar, together with the initial mass fraction of heptane in liquid phase ranging from 0 to 1. The results indicate firstly, the effect of non-ideal behavior on evaporation constant and temperature evolution is more pronounced for the droplets with initial heptane mass fraction of 25% and 50% inside the mixture. This reveals that when the lighter component dominates the mixture, the assumption of an ideal mixture is less accurate. Secondly, for the non-ideal system, the liquid phase composition is an important factor in deciding the evaporation order of different components in the mixture. In some situations, the less volatile fuel evaporates faster than the more volatile part in the mixture. Moreover, the influence of non-ideal behavior is attenuated under high ambient temperature and pressure conditions as presented by the relatively smaller value of separation factor. Lastly, the obtained simulation results were analyzed with the rainbow theory by predicting the scattering light patterns by droplet at the rainbow angle. The difference in the scattering light patterns was analyzed.