Multiphysics Modeling of Microwave Vacuum Freeze-Drying of Blueberries Based on Saturation-Dependent Dielectric Properties

Microwave vacuum freeze drying (MVFD) is a promising technology for processing heat-sensitive porous materials. However, the non-uniformity of electromagnetic energy distribution often leads to local overheating and quality deterioration. This paper presents a multiphysics numerical model coupling electromagnetic fields, heat transfer in porous media, and mass transport based on Darcy's law. To address the issue of thermal runaway in late-stage drying, a mixture rule for dielectric properties dependent on ice saturation is introduced. The simulation analyzes the electric field distribution, temperature evolution, and pressure-driven vapor migration. Results indicate that the internal pressure gradient is the dominant mechanism for mass transfer, and the proposed variable dielectric model effectively predicts the drying process while maintaining the material temperature below the triple point.