Numerical study on conjugate heat and mass transfer process within porous media with dielectric cores during microwave freeze drying

Microwave freeze drying of porous media with dielectric cores was studied numerically. The sets of transient governing equations developed for the conjugate heat and mass transfer process was derived and solved with variable time-step finite volume method. Numerical results show that two sublimation fronts do exist within the porous media, and this is a new phenomenon associated with dielectric core. The two sublimation fronts model proposed can successfully simulate this drying process of porous media with dielectric cores. A dramatic drying time saving could be obtained with proper selection of dielectric cores. Comparing with that of porous media without dielectric core, the drying time per unit volume decreases by 8%, 19%, 33% and 48%, for the porous media with 1.0, 1.5, 2.0 and 2.5mm dielectric core, respectively. It is found that the drying process is mostly influenced by the core size and the loss factor of the core material. Bigger loss factor results in a shorter drying time under the same electric field strength.