Experimental Study on Flash Evaporation Characteristics of Saline Droplet in Vacuum

Flash evaporation of saline (aqueous Na Cl solution) droplet in vacuum was experimentally studied with the lab-built test platform.The influence of the pressure, Na Cl concentration and initial temperature on the flash-evaporation behavior and phase transition of the droplets was investigated.The results show that the pressure, Na Cl-concentration and initial temperature of saline droplet all had a major impact.To be specific, depending on the Na Cl-concentration and pressure, the vacuum flash evaporation of saline-droplet, much more complicated than that of water-droplet, displayed five distinctive phenomena, including the steady water-evaporation, bubble growth-evaporation, steady evaporation-solidification; bubble growth-solidification and salt precipitation.At the eutectic concentration (22.4%), Na Cl precipitation occurred, lasting longer than solidification and continuously releasing some heat; whereas at the brine concentration (< 5%), droplet solidification happened.Salt can be much more rapidly extracted from saline droplets at a higher initial temperature and a lower pressure (< 1000 Pa).