Study On Prediction And Control Methods Of Residual Moisture Content Of Freeze Drying Process

Compared with the traditional hot drying methods, freeze drying method is conducive to maintain the original chemical composition and physical properties of materials and the substances are loose and porous after drying, easy to dissolve and rehydration and so on. So freeze drying technology has become more and more widely used in food industry, pharmaceutical industry and biological products. Residual moisture content is one of the most important factors that affect the freeze drying effect.Based on the analysis of the basic principle of freeze drying and physical mechanism,studies on modeling and simulation method of the freeze drying process are carried out,so as to achieve the effective prediction and control of residual moisture content during freeze drying. The concrete work includes:(1) study on the simulation method of freeze drying process. The simulation method of freeze-drying process is proposed based on finite element theory and the dynamic meshing technology, the simulation model of sublimation drying process and desorption drying process of freeze drying is established and researched based on multidimensional dynamic model. Through the study of the distribution and variation of temperature, pressure and residual moisture content in the process of freeze drying, the validity and reliability of the simulation method is confirmed.(2) The prediction method of residual moisture content in freeze drying process is studied. The calculation methods of residual moisture is proposed based on the present simulation method of freeze drying process. The simulation study of the residual moisture content of sublimation drying process and desorption drying process. The results showed that the shelf temperature, pressure, material thickness and drying time during freeze drying will be of influence to the residual moisture content of freeze drying process. The study on residual moisture of lyophilized red blood cells is carried out using nuclear magnetic resonance method, and it is found that the simulation resluts and experimental resluts are in good agreement by comparison. Finally, the prediction method of residual moisture content is put forward based on the simulation and experimental results of freeze drying.(3) The control method of the residual moisture content during the freeze drying process is studied. Through analyze the level that the shelf temperature, pressure and thedrying time of freeze drying process influence the residual moisture content and the difficulty level that the different drying conditions during freeze drying process are carried out, the control method of freeze drying process parameters is put forward to control the residual water content.