| Offer the heat resource to freeze drying by microwave energy were considered as changing the heat input method in essence. Reports show that microwave freeze drying has the higher efficiency than the other general method freeze drying. In order to explore the inherent law and predict the variation process the theoretical and experimental studies were conducted on the process of microwave freeze drying. On the aspect of theory, the mass transfer process of microwave freeze drying was studied. The correlative conclusion of low press gas mass transfer in capillaries was inported to the mass transfer process of microwave freeze drying. Introduce the expression of the diffusivity which based on the theory of low press gas mass transfer in capillaries. The model of microwave freeze drying was founded, and programme to simulate the temperature profile and the curve of drying process. Compare the simulate result with the model which based on the experimental diffusivity. Discuss the key manipulative parameter such as intensity of electric field,the pressure in the cavity,the material's thickness etc about the microwave frezze drying. The technics flow of microwave freeze drying was discussed too. The restrict condition in the technics such as general condition,interactional condition,microwave condition was discussed. As to the experimental study, make use of the reported date, the comparison of the experimental drying curves of microwave freeze drying of beef with those predicted by the theory shows a reasonable agreement in the phase of sublimation. It's showed that the maximum difference less than 10 percent in the phase of sublimation. It's showed that according the theory of low pressure gas mass transfer in capillaries using the materiel's microstructure, molecule's mean free path, vapor's state parameter, vapor's physical characteristic to express the diffusivity is a reasonable method. |
