Coupled heat and moisture transfer during microwave vacuum drying

A general mechanistic model has been developed to describe the coupled heat and moisture transfer during dielectrically-assisted drying of porous materials. The model considers the moisture transfer as the combination of the liquid water and vapor water transfer that takes place simultaneously. The heat transfer is based on the energy conservation of the sensible heat, latent heat and source heat of microwave power. The derived heat and moisture transfer equations are fully coupled. When the temperature gradient induced moisture transfer is sufficiently small, the moisture transfer equation degenerates to the isothermal equation. By using the finite element method, the fully coupled equations have been solved numerically and applied to simulate the heat and moisture transfer during microwave vacuum drying of a concentrated water soluble food paste. The predicted drying rate is in good agreement with the experimental data.