Résumé
Microwave-material interactions and electromagnetic propagation phenomena are important to optimize the microwave heating process of food samples. In this study, a 3D numerical modelling of a TE10 rectangular waveguide including microwave antenna and impedance matching elements is proposed. The microwave applicator is aimed to process both solid and liquid food samples. The model illustrates the standing wave patterns and microwave absorbed power within the cavity by taking into account the influence of the screw tuner, quartz windows, shorting plunger, and additional dielectric support plates. The results reveal the importance to consider the real cavity design and the precise dielectric characterization to predict accurate temperature profiles within the food product during the microwave heating. Such a model can be now be used to optimize the food sample geometry to achieve minimum reflected power and better heating uniformity. Introduction Microwave heating processes for food products are used industrially for various unit operations such as tempering, drying, pasteurization 1. During a microwave heating process, the energy contained into an electromagnetic wave is converted into heat within dielectric materials. This selective volumetric heating mechanism allows a considerable reduction in processing time and increases the energy efficiency of the process 2. However, one of the main challenges is the heterogeneous electric field distribution within the food matrix which could result in hot and cold spots 3. Since electromagnetic field measurements within a microwave cavity are particularly difficult to perform, the numerical modeling and simulation appear as a promising tool to understand, predict and control the process, as well as, to optimize the design of equipment and packaging 4. As many factors influence the degree of interaction between the microwaves and the material, the model needs to take into account both geometrical details of the microwave cavity and the physical properties of the materials under consideration. These include dielectric, thermal and physical properties of the product and the dielectric materials (volume, geometry and location) and the design of the microwave cavity 5. The purpose of this study is to investigate the influence of the cavity design and dielectric properties during the microwave processing of solid and liquid food products.