A mathematical model was developed to simulate the heat and mass transfer of evaporation and salt crystallization process of a saline (aqueous NaCl solution) droplet during depressurization. The model considered the formation of porous salt crust at the droplet surface

the air flow around the droplet caused by pressure drop

the mass diffusion of vapor through porous medium and the heat transfers due to evaporation and convection at the droplet surface. By comparing the numerical results with the experimental data

the validity of the present model was verified. Through numerical calculations

the variations of droplet surface temperature and droplet mass with time were obtained

and the different characteristics of droplet evaporation and crystallization process under low pressure environment and atmospheric environment were analyzed. The results showed that the temperature variation of a saline droplet during evaporation and salt crystallization process under reduced pressure can be divided into four stages: the stage of temperature drop

the temperature recover stage

the equilibrium temperature stage

and the temperature rising stage. During the equilibrium temperature stage

the movement of salt crust interface was slower

with the evaporation process

the size of liquid core decreased continuously

and then the movement of salt crust interface was quicker. The effect of ambient pressure on evaporation and salt crystallization process of a brine droplet was theoretically analyzed. With a lower ambient pressure

the equilibrium temperature was lower and the time for salt completely precipitated was shorter.