To investigate the enhanced effect of wave-absorbing material assisted microwave heating on traditional freeze-drying

a multiphase transport mathematical model conjugating temperature field

concentration field and electromagnetic field was developed and numerically solved. The sintered silicon carbide (SiC) was used as the absorbing material and the mannitol aqueous solution was used. Microwave freeze-drying experiments of mannitol aqueous solution were carried out

and dielectric properties of mannitol solid powder were measured. Both numerical and experimental results show that using wave-absorbing material as the supporting pad of sample can effectively enhance the microwave freeze-drying process. Under the typical operating conditions

microwave freeze-drying time of the initially unsaturated material can be 18% and 30%

respectively

shorter than the traditional freeze-drying process of the initially unsaturated and conventionally saturated samples. Excellent agreements were received between experimental measurements and model predictions. This indicates that the proposed freeze-drying method can achieve the simultaneous enhancement of heat and mass transfer. Based on the profiles of temperature

ice saturation and electrical field strength

mechanisms of heat and mass transfer

as well as electromagnetic wave propagation and dissipation inside a sample were analyzed during drying. The accumulatively absorbed energy of radiation and microwave during drying was almost the same as those of traditional freeze-drying of the initially saturated and unsaturated samples. This demonstrates that the proposed method only increases the energy utilization so as to largely reduce the freeze-drying time.