Numerical Simulation And Verification On Freeze Drying Of Initially Unsaturated Porous Material

In today’s production, freeze-drying technology plays a very important role especially in the field of food, medicine, biological products. The quality of the samples treated by freeze-drying process is the best in all the drying technologies. However, the character of high energy consumption has been restricting the development of freeze-drying. Therefore,How to improve the economy of the process, reduce energy consumption has become the priority among the research.This paper established a two-dimensional mathematical model of freeze drying process and put it into the multiphysics simulation software COMSOL Multiphysics 4.3a for its numerical solution. Put forward two new adsorption-desorption equilibrium relationship and analyzes its application conditions. Compared the simulation data and experimental data of different initial saturation material in the same conditions with experiment process. Analyze the mechanism of heat and mass transfer in porous media. Explore the effect of environmental radiation temperature, chamber pressure and material pre-freezing temperature on freeze-drying process.The results show that:the initial unsaturated materials can significantly shorten the drying time and the simulated curves also can agree with the experimental data. At low initial saturation conditions, Kelvin equation is superior to Readhead adsorption relationship,but at high initial saturation condition, Readhead adsorption relationship is better than Kelvin equation. By analyzing the distribution of material temperature and saturation we can know that:sublimation process happened not only in the sublimation surface but also in the frozen region of the sample. Along with the drying process the sublimation interface move to the material internal gradually.By changing the typical operating conditions of the material we can know that:Appropriately increase of environmental radiation temperature, reduce the drying chamber pressure can improve the freeze drying rate, shorten the freeze-drying time, reduce energy consumption, improve the economy of the whole freeze-drying process.