Heat and Mass Transfer in Microwave Processing

This chapter focuses on the heat and mass transfer in microwave processing. The heat and mass transfer characteristics of microwave processing systems are of considerable interest for materials development and process engineering. The ability of microwave radiation to penetrate and couple with materials provides an attractive means of obtaining controlled and precise heating. Microwave appliances have three major components—a microwave generator, a waveguide, and an applicator. It is important to appreciate the role of each component to understand how microwave ovens operate. Electrical properties dictate the nature of microwave-material interactions. Metals (electrical conductors) are excellent reflectors and are not, in general, heated significantly by microwaves. Electromagnetic field intensity and distribution are prime factors that determine microwave absorption. The unique character of heating in microwave processing can be understood only by appreciating how electromagnetic radiation propagates and is absorbed by materials. During microwave heating of porous materials, temperature gradients and internal evaporation can promote transport of mobile components (liquids and gases). As compared with conventional surface heating, microwaves can generally provide faster, selective, and more uniform heating. Microwaves offer many potential benefits for processing materials—time and energy savings, improved product quality, better process control, and new process applications.