Study On Gas Liquid Mass Transfer Of Wiped-film Molecular Distillation

Molecular distillation (MD) is a special liquid-liquid separation technology, it has a lot of applications in various fields because of its unique separation mechanism. It is based on the difference of mean free path of light and heavy components. Molecular distillation is accepted more and more attention since the middle of last century, and has already been widely used in petrochemical industry, food industry, cosmetic industry, pharmaceutical industry and other industries in recent years.The gas-liquid mass transfer in wiped-film molecular distillation is investigated by desorption experiment of oxygen-enriched water. The performance of different operating parameters including the temperature, feeding speed, the rotate speed is investigated here.We computed the gas-liquid mass transfer coefficient in wiped-film molecular distillation by the empirical correlation of convective mass transfer GA=NAS=kcS(cAb-cAs). And we've also summarized the special rules of kc: temperature and feeding speed have obvious influences on kc, kc is in direct proportion to temperature and feeding speed; the rotate speed has little influence on kc. We modified the empirical correlation of kc by mathematical methods and obtained a new correlation of kc which is more applicable to wiped-film molecular distillation. And the mathematical modification is dimensionless. The influence of gas-liquid interface which is decided by both rotate rate and feeding speed is considered in the new correlation of kc. And we also built an empirical mass transfer representation of wiped-film molecular distillation by dimensionless parameters Sh,Sc and Re.At last we built a two-dimension wiped-film molecular distillation physical model to simulate the liquid-gas mass transfer by using the software FLUENT, according to double-film theory. We achieved two phases mass transfer simulation successfully by compiling UDS function and UDF function. First we inspected and verified the independency of the grid, and chose 40000 as the final grid number. This method can not only make the simulation very precise, but also save the computating time.Through the simulation we can know that the oxygen mole fraction of liquid bulk decreases along the flow direction. And the simulation results and the experimental results are very close to some extent. We simplified the physical model because of limitation of time and other factors, and did not consider the influence of rotate rate to gas-liquid mass transfer.