Numerical investigation on the coupling effect of sessile ethanol droplet evaporation and the induced thermal flow in its pure vapor environment at low pressure

Abstract

In order to reveal the coupling characteristics of sessile ethanol droplet evaporation and induced thermal flow in its pure vapor system at low pressure, a series of three-dimensional numerical simulations were carried out on the ethanol droplet evaporation on a copper substrate. The droplet radius is 2.5 mm. The droplet height ranges from 2.2 to 0.4 mm. To investigate the effect of vapor pressure, two pressure ratios (η) of 0.9 and 0.6 are chosen. The results show that, when η = 0.9, regardless of the droplet height, the surface temperature distribution in most areas is always uniform. However, when η = 0.6, several surface thermal patterns appear. Because of the evaporation, the substrate temperature distribution always has the lowest value near the contact line. The thermal pattern evolution will affect the evaporation rate and the substrate temperature distribution dynamically. When η = 0.6, the evaporation rate shows a non-monotonic variation trend with the decrease of the height. Although the droplet size is larger than the capillary length, buoyancy has little effect on the thermal pattern evolution and evaporation rate.