Study on mechanism and key parameters of sessile droplets flash evaporation under reduced pressure

Droplet flash evaporation is widely used in waste heat recovery, artificial ice making and other industrial fields. The vigorous flash evaporation leads to the flash explosion, which might cause damage to the internal structure of the flash evaporation chamber. Therefore, how to suppress flash explosions for industrial production safety is imperatively studied. With a high-speed camera system, the flash evaporation process of sessile droplets (deionized water and desulfurization slurry) is experimentally investigated and the duration of the flash explosion is recorded. The finite element method establishes the droplet flash evaporation model, and the internal flow and heat transfer process of single/multiple droplets are numerically simulated. The results show that the initial diameter of the droplet can directly affect its internal temperature change rate, thus controlling the internal phase transition process and the occurrence of droplet flash explosion. In this paper, the critical diameter of droplet flash explosion under different conditions and effective methods to suppress flash explosion are pinpointed, including increasing ambient air pressure, reducing the initial temperature of the droplet, reducing droplet size, and using a low thermal conductivity substrate. In addition, the numerical results show that the internal flow of droplets is dominated by thermal convection in the flash evaporation. The three-dimensional simulation of a multi-droplet array shows that the decrease in flash evaporation rate is the low vapor concentration gradient near droplets.