ABSTRACT
Microwave (MW) and radio-frequency (RF) heating are not only highly intensive but also cost-incurred methods of thermal treatment (Sanio, 1989; Sanio and Schmidt, 1989). For these reasons, hybrid technologies involving combinations of various driving forces for heat and mass transfer are preferable. Typical examples are RF-and MW-assisted convective drying, where the high-frequency electromagnetic energy may be applied at different drying stages to supplement thermal energy supplied with drying air. By adjusting the balance among component technologies, it is possible to optimize the hybrid systems in terms of the process effectiveness and cost. Of the various hybrid systems based on MW irradiation, MW vacuum drying and MW freeze-drying (F-D) have found the widest applications in dehydrating fruits, foods, and thermolabile biomaterials such as microbial strains, plasmas, serums, enzymes, and others (Kudra, 1990, 1999; Kudra and Strumillo, 1998). Therefore, this chapter focuses on two prospective but less-common MW-assisted drying technologies.
