Numerical simulation on the influence of gravity on binary droplet evaporation under different conditions

• Evaporation behaviors for sessile, pendant and zero-gravity BMD are conducted. • Influence of substrate temperature and droplet concentration is investigated. • Difference in droplet life is determined by internal and external flow. • Higher temperature and concentration increase the evaporation rate disparity. Droplet evaporation is a common physical phenomenon in daily life and industrial production. It is of great significance to understand its evaporation characteristics. This study employs the finite element method coupled with moving mesh technology to investigate the influence of gravity on the evaporation dynamics of ethanol–water binary mixture droplets (BMD) under different substrate temperatures and initial ethanol mass fractions. The results indicate that the evaporation rate of BMD is the slowest under zero-gravity condition and the fastest for the sessile droplet. The zero-gravity BMD exhibits a 27.6% longer lifespan compared with the sessile BMD. As the substrate temperature increases, the lifespan difference between sessile and pendant BMDs becomes more pronounced. With the increasing initial ethanol mass fraction, the volume difference between sessile and pendant droplets decreases in the later stages. This research promotes a deeper understanding of the mass and heat transfer mechanisms in the evaporation process of BMD.