Numerical simulation on freeze drying with dielectric material assisted microwave heating

The effects of the dielectric material on the microwave freeze-drying process were theoretically studied by mathematically solving the heat and mass transfer model considering the hygroscopic effect with a moving boundary in the porous media. Sintered silicon carbide (SiC) was used as the dielectric material, and the mannitol, a typical pharmaceutical excipient, was selected as the solute in aqueous solution. Simulation results show that the dielectric material can significantly enhance the microwave freeze drying rate under the experimental operating conditions, especially when the solid content in the freeze dried solution is very low or the solid product has a very small dielectric loss factor. Comparisons of the drying curves display good agreements between experimental measurements and model predictions. Based on the profiles of ice saturation and temperature, mechanisms of heat and mass transfer inside the material were analyzed, and the drying rate-controlling factor was discussed.