The effect of dielectric properties on microwave drying kinetics

The question of when to apply microwaves during the drying of porous media has created much interest over the past decade and still remains largely unanswered. To assist with the elucidation of this question, a model for the drying process has been constructed in which the dielectric properties are dependant on moisture and temperature. The complexity and costs involved in measuring the distribution of such quantities as moisture content, temperature, pressure, and power generated during a combined microwave/convective drying experiment highlight the need for mathematical modelling as an essential ingredient in the research of the topic. Numerical simulations can aid in the design and understanding of dryers and can indicate the effectiveness of the microwave energy during the drying process. The developed mathematical model can demonstrate not only the effects of the different functional relationships for the dielectric properties on the drying kinetics, but more importantly help in the decision of when to apply microwaves during the drying process. Simulation results are presented for the combined microwave/convective drying of a homogeneous, isotropic, porous material in which the permittivities depend on saturation alone, temperature alone, and on a combination of saturation and temperature.