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Microwave power is seen as a promising alternative to conventional methods for drying freshly harvested grains to safe storage moisture levels. In an attempt to elaborate a continuous flow microwave dryer, the optimum operating characteristics of a prototype microwave antenna were investigated during a low power microwave drying simulation with corn at three different moisture content levels (15%, 23% and 30% w.b.). The antenna consisted of a slotted waveguide with the orientation and width of the slots being the main points of investigation. / The optimum angle of the slots with respect to the direction of propagation of the travelling wave was found to be in the neighbourhood of 55° at all moisture contents. Slots 13 mm wide gave better results than the 6 mm ones which are often suggested in literature.

Microwave drying of corn was investigated at selected levels of initial moisture content, absorbed power by grain, and temperature and superficial velocity of air at inlet. A surface-wave applicator was used to couple microwaves with the corn. / The drying rate curves indicated that the microwave drying of corn took place in the falling rate period. It was hypothesized that diffusion is the controlling mechanism for moisture transfer from within the kernel in microwave drying of corn. / A mathematical model was developed to describe the change in moisture content at the surface as a function of the free moisture content of corn. The diffusion model employing varying surface conditions was used to describe the microwave drying process. An Arrhenius type equation was developed to describe the relationship between the diffusion coefficient and the outlet air temperature. The diffusion coefficient values varied from 0.0008 to 0.0082 cm$ sp2$/h when constant levels of microwave power were applied continuously for drying corn. Equilibrium moisture content was determined and regression equations were developed to describe the EMC with microwave power and air velocity. / The diffusion coefficient increased with the levels of absorbed power, decreased with increasing air velocity but remained insensitive to the inlet air temperature when microwaves were applied continuously for drying corn. The increased drying rates at higher power levels reduced the drying time considerably but at the cost of energy loss through the passing air and reduced germination and bulk density of dried corn. Application of absorbed microwave power at 0.25 W/g resulted in greater than 92% germination of dried corn. Deleterious effects on product quality was observed when the applied power exceeded 0.75 W/g. / Pulsed and variable microwave power effects were investigated in order to optimize the drying process. Time for drying corn increased but the effective duration for which microwaves were applied and the energy requirement in the pulsed mode was lower compared to both continuous and variable microwave operation.

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The potential of granular zeolites as a heating medium for drying corn was evaluated in a batch type experimental dryer. At temperatures from 150-250$ sp circ$C and residence times of 3-8 minutes, synthetic zeolites (4A and 13X) removed 9-18 percentage points from the initial moisture of corn. These values were about double those of sand, the most commonly used particulate medium. / Using an adiabatic dryer, the kinetics of moisture sorption in corn-zeolite mixtures was investigated. The heating medium in this part of the study was a natural zeolite (chabazite) and the corn was yellow dent type. Diffusivity values for corn were 1.012 $ times$ 10$ sp{-5}$ $-$ 3.127 $ times$ 10$ sp{-5}$ cm$ sp2$/s with zeolite at temperatures of 140-220$ sp circ$C. These values are much smaller than those for zeolite. Therefore, it is believed that the diffusion of moisture in corn itself is the main resistance to the transfer of moisture. The heat transfer coefficient between corn and zeolite was found to be in the range of 50-312 W/m$ sp2 cdot$K. Luikov's model for simultaneous heat and mass transfer was applied to corn-zeolite mixtures and the equations were solved by the Numerical Method of Lines (NMOL). These numerical solutions agreed closely with the experimental data. / The processed corn was subjected to in vivo and chemical analyses. Results of feeding experiments using laboratory rats did not indicate that the nutritive quality of the processed corn was adversely affected. Similarly, the acid detergent fibre analysis did not show a significant reduction in the availability of corn protein.

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