Numerical simulation of heat and mass transient behavior of single hexadecane droplet under forced convective conditions

A droplet evaporation model based on the direct numerical method and the high-fidelity interface capturing methodology is developed to simulate the evaporation process of liquid droplets under a high-temperature convective environment. The coupled Level-set and Volume of Fluid method is applied to describe the droplet interface. The phase change rate is derived directly from the mass fraction gradient at the droplet interface. After verifying the accuracy of our model with the experimental results and the analytical solution, the evaporation process of droplet under high temperature and forced convective condition is examined. The results revealed that convection breaks the uniform distribution of temperature and concentration. The temporal behaviors of Nusselt and Sherwood number under convective environment are similar, as classified by two stages, i.e. the transient variation period and steady-state stage. In addition, increasing ambient temperature from 500 K to 800 K promotes the reduction rate of droplet volume by around 5 times. However, it restrains the convective heat and mass transfer rates as a result of the reduction in Reynolds number and the intensity of surface blowing. It is deduced that high temperature is beneficial for conductive heat transfer but unfavorable to the convective heat and mass transportation. By contrast, enhancing free-stream velocity is exceedingly beneficial to the convective heat and mass transfer rates as the convective heat and mass transfer rates in steady-state are promoted by 25% and 27%, respectively, when the free-stream velocity grows from 0.5 to 2.0 m/s. Finally, the variation of Sh and Nu with the Reynolds number obtained in this work is compared with the results of empirical correlations proposed by Ranz-Marshall [1] and Clift et al. [2]. It is concluded that, in the present research range of 1.5 <= Re <= 12.8 and 500 K <= T-infinity <= 800 K, the modified Ranz-Marshall correlation has a better capability in predicting the Sh and Nu. This reveals that when droplets expose to a high-temperature free-stream with a low Reynolds number, the dynamical effects induced by evaporation is active and cannot be neglected. (C) 2020 Published by Elsevier Ltd.

Automated summary

A droplet evaporation model was developed based on the direct numerical method and high-fidelity interface capturing methodology to simulate the evaporation process under high-temperature convective conditions. Convection was found to disrupt the uniform distribution of temperature and concentration. Increasing ambient temperature promoted droplet volume reduction rate but restrained convective heat and mass transfer rates.