Study Of Subcooled Solidification Process Of A Droplet During Depressurization

When the ambient pressure drops rapidly,the droplet evaporates quickly,the temperature drops,and the droplet is solidified after the drop of temperature in the low pressure environment.This process is widely used in many fields in recent years,including vacuum cooling,ice slurry preparation,food preservation etc..In this paper,experimental and theoretical studies are used to study the solidification process of a single droplet in a fast buck.In the experimental study,the liquid drop suspension method was used to carry out the experiment on a variety of working fluids,including distilled water,acetic acid and sucrose solution.The initial environmental pressure is 1atmosheric,the final ambient pressure range is 200~9000Pa,the initial temperature of droplet is 10~50 C,the initial droplet diameter range is 0.8~3mm.The experimental results show that the droplet temperature during the subcooled solidification process experiences“decrease-jump-maintain near the freezing point-rapid decline-stable” five stages,which correspond to the five physical processes “evaporation-latent heat of solidification-sublimation and solidification interaction-sublimation heat-sublimation with the convective heat transfer on the surface” of five heat and mass transfer process.Sucrose solution droplets due to its high viscosity,better show the relationship between liquid droplet temperature and bubble growth process,burst the bubble burst inside the droplets will take some of the heat,causing rapid decrease in droplet temperature.In the aspect of theory,a mathematical model was developed to simulate the subcooled solidification process within a single droplet during flash evaporation.The model was based on droplet flash model,solidification and solidification,and coupled the kinematical condition of the solidification interface and the the energy equation of solidification and sublimation.The calculated results agree well with the experimental data,which shows the variation of droplet temperature and the movement of the solidification interface.The results show that the Environmental pressure is lower,the smaller the droplet size,the surface temperature decreases faster,faster solidification,solidification time is shorter,the temperature drops increases quickly.