Liquid phase model and its coupling interaction with the ambient gas for the droplet heating and evaporation of highly volatile R134a

Abstract

Droplet evaporation plays a decisive role in determining the evolutions of droplet temperature, diameter, and velocity in sprays with low saturation temperature and high volatile mediums. This study conducts a comparative analysis of liquid phase models for single droplet heating and evaporation of high volatile R134a. Three traditional liquid phase models based on the assumption of infinitely large liquid thermal conductivity (lumped), limited thermal conductivity, and effective thermal conductivity and a recently proposed third-order polynomial temperature profile (third-order) liquid phase model based on the presentation of the temperature profile inside the droplet in cubic polynomial form without solving the heat conduction equation are introduced to predict the temporal evolutions of droplet temperature, diameter, and velocity, and the spatial evolution of temperature within the droplet. The coupling of heat and mass transfer between the droplet and its surrounding gas is incorporated into the liquid phase models to investigate its effect on droplet evaporation. The droplet temperature first undergoes a rapid decrease at the transient stage of evaporation and then decreases slowly to the minimum temperature (Tmin). The droplet temperature in the transient stage depends highly on the choice of liquid phase models. Tmin is mostly unaffected by the liquid phase models. The dependence of the droplet diameter at the transient stage of evaporation on the choice of the liquid phase model is stronger compared with the following steady stage. The droplet velocity is rarely influenced in the whole evaporation. The liquid phase models incorporating the coupling weaken the evaporation intensity, resulting in a high droplet temperature and large droplet diameter. The third-order liquid phase model incorporating the coupling model predicts Tmin and agrees with the experimental data. This model can reflect reasonably the heat transfer enhancement by the recirculation inside the droplet for moving droplet.