ABSTRACT
Mathematical modeling of dielectrically-enhanced drying is generally more difficult than modeling of conventional drying. The microwave and radiofrequency field intensity is not uniformly distributed, and the heating effects of the field differ between various species and phases within a wet material. Elevation of internal temperatures, often to the boiling point of water, can produce significant internal pressure gradients. However, these phenomena combine to produce the unique production benefits of dielectrically-enhanced drying.
A general description of dielectric heating is presented. The dielectric properties of wet materials and their dependence on moisture, temperature, and composition are considered in the context of their behavior during dielectricallyenhanced drying. The effects of the dielectric heating on the transport mechanisms of moisture in nonhygroscopic and hygroscopic materials are highlighted. Heat and mass transfer in drying wet porous media are discussed with special consideration to the effects of internal heat generation due to dielectric heating in microwave and radio-frequency fields. Several fundamental physical models for dielectrically-enhanced drying are introduced and reviewed here with a view toward achieving better understanding of the physical nature of this process and providing a more rational basis for process design.
