Microwave penetration depth modeling in the dehydration of capillary-porous media

Abstract

Drying is a widely utilized technique for food preservation, typically involving the transfer of thermal energy to the product's surface via convection, conduction, or radiation. Among these methods, microwave drying has emerged as a particularly effective alternative. The physics behind microwave drying is sophisticated, as energy absorption occurs through two primary mechanisms: ionic conductivity and dipole relaxation. For high-moisture substances, dipole relaxation is the dominant process. When a dielectric material is subjected to an electric field, its ions, atoms, and molecules become excited; the resulting motion and subsequent collisions convert kinetic energy into thermal energy. Developing a mathematical model for the microwave heating of capillary-porous bodies allows for new analytical solutions. These solutions make it possible to precisely determine how various parameters-such as electric field strength, processing duration, and wave penetration depth-impact drying intensity. Penetration depth is a decisive factor in ensuring heating uniformity and efficiency. Our modeling and calculations for a product with 40% moisture content situated this parameter between 2 and 6 cm. The numerical solution derived for penetration depth is a critical factor in the dehydration of capillary-porous materials. Furthermore, it provides a necessary benchmark for evaluating the accuracy and reliability of other theoretical models. Acknowledgments: Institutional Project 020405 “Optimizing food processing technologies in the context of the circular bioeconomy and climate change”, Bio-OpTehPAS, being implemented at the Technical University of Moldova.