Experimental and numerical investigations on flash evaporation of a sessile droplet under reduced pressure

Abstract

Flash evaporation of droplets under reduced pressures is versatile in industrial applications for its low energy consumption. More vigorous flash explosions may occur by the subsecond expansion of internal bubbles, leading to inefficient heat transfer and facility damage. In this work, we propose using the aerosol with an inherent low thermal conductivity as the substrate to study the flash evaporation of sessile droplets, which reduces the number of nucleate sites and suppresses the flash explosion, in contrast to the pendant one. We experimentally reveal the effect of ambient pressure, initial droplet temperature, and size on droplet temperature evolution and evaporation rate. A revised diffusion coefficient is proposed based on the experimental droplet lifetime with the aid of D2-law, which is utilized in axisymmetric simulations for acquiring the flow field, temperature, and vapor concentration distribution. The analogy between experimental and numerical results has demonstrated the validity of this revision. The interplay of two convection flows aroused by the Marangoni effect and thermal convection is displayed at the early stage of flash evaporation, and the latter is predominant for the rest of evaporation.