A slotted waveguide antenna for grain drying

Convection drying using fossil fuel combustion is the most widely used method for drying freshly harvested grains to safe storage levels. When hot air is used to dry grains, a slow conduction heat transfer takes place from the grain surface towards the inside. The outer layers of the kernel arc dried first and become less permeable, creating case hardening (Fanslow et al., 1971). The mass transfer of the moisture however, goes from the inside of the kernel to the suface and is slowed down by the counter current heat transfer. Microwave energy can be used to dry grains in a volumetric process and thus eliminate the use of fossil fuels in regions where hydro power is available (Raghavan et al., 1993). When microwaves are used to dry grams, both heat and mass transfer are instantaneous and emerge out of the kernel. Researchers have studied the drying behavior of particulate food materials in a microwave field (Hall. 1963; Fanslow and Saul, 1971; Bhartia et al., 1973; Shivhare et al., 1991). Slotted waveguides have been successfully used to couple electromagnetic energy to materials for heating and drying purposes (Rueggeberg, 1980; Metaxas and Meredith. 1983) and for plasma applications (Ji and Gerling, 1988; Sauvé et al., 1993). The present study was aimed at determining the optimal operating parameters of a slotted waveguide applicator for continuous flow grain drying.