Numerical Simulation Of Heat And Mass Transfer Process Of Multicomponent Droplet During Depressurization

The evaporation characteristics of multicomponent droplet and the bubble growth within water droplet during flash evaporation under rapid reduced pressure were studied. The evaporation characteristics of multicomponent droplet during depressurization can be applied in seawater desalination, aerospace liquid discharging and other fields,the research is helpful for understanding the heat and mass transfer of multicomponent phase transition. Multicomponent droplet evaporation involves the transient heat transfer at droplet surface, multicomponent phase transition,and the mass diffusion between the components during evaporation process. Also, the change of droplet internal component concentration increase the complexity of the problem。This paper adopts the theoretical research methods, and the evaporation model of multicompoment droplet during depressurization was established. By comparing the numerical results with experimental data, the validity of the present model was verified. And then, through numerical calculations, the main factors affecting the evaporation characteristics of multicomponent droplets were analyzed. The main research contents are:(1) Theoretical study of evaporation process of a salined droplet during depressurization. The evaporation model of a saline droplet during depressurization was developed based on energy conservation equation and mass diffusion equation to describe the temperature distribution and the concentration distribution within droplet. The main influencing factors of evaporation process were analyzed by numerical calculations.(2) Theoretical study of salt crystallization process of a saline droplet during depressurized evaporation. With the evaporation process,when the concentration of saline droplet is higher than the saturation concentration under corresponding temperature,salt crystallization occurs at the droplet surface. The ‘four stage model’ was used to investigate the temperature variation of a saline droplet during depressurized evaporation, which considered the formation process of salt shell at the droplet surface, the heat release of salt crystallization, and the influence of salinity on droplet evaporation characteristics during salt precipitation.(3) Theoretical study of evaporation process of a bicomponent t alcohol solution droplet during depressurization. Alcohol solution droplet contains two kinds of volatile components, two components influence each other during evaporation process. The ‘bicomponent droplet evaporation model’ was applied, which introduced active fators of different components to consider the quality of droplet evaporation rate at droplet surface. Through numerical calculation, the droplet internal temperature distribution, concentration distribution and the variation of droplet dimensionless size with time were obtained. The main foctors affecting the droplet temperation variation and the droplet size variation were analyzed.(4) The droplet flash evaporation accompanying with bubble growth process under rapid decompression environment is an important part of falsh spray. The bubble growth during flash evaporation of a water droplet was theoretically studied. The model was based on Schrage’s droplet flash model, and the bubble growth dynamic equation(the Rayleigh equation) was introduced. Through numerical calculation, the main influencing factors of bubble growth were analyzed.