Numerical modelling of an innovative microwave assisted freezing process

This study aimed to model an innovative process of pulsed microwave assisted freezing (MAF), which was expected to improve frozen product quality. The phase change model was based on spherical ice crystal growth and an original enthalpy formulation. The objective was to understand better the thermal interactions between microwaves and a product being frozen in a TE10 waveguide in which nitrogen gas and microwaves reach the product on the top surface. The 2D model was validated against the literature data and used to perform numerical simulations. The freezing front location and the reflection at air-product interfaces have a large impact on microwave behaviour in the product, especially on hot-spot displacement. As in some experimental works, temperature oscillations were observed. It is shown that their amplitude is related to the pulse duration. These results will help in designing experimental procedures to study the interest of using low energy pulsed microwaves during freezing.