| Understanding of the interactions between microwaves and dielectric materials is of great importance in food applications. Such interactions lead to complex variations in heating patterns that are of critical importance in food product and process development. The focus of this research is to study these interactions between food and oven parameters and develop useful relationships between the parameters for practical applications.; The approach combines comprehensive numerical modeling with experimentation. Maxwell's equations are solved numerically using a finite element method for a microwave oven system (such as the domestic oven) that includes excitation, waveguide, and cavity and food materials of various size, shape and properties. Temperature effects are included by developing detailed methodology for coupled solution of the Maxwell's equation with energy equation for a solid. Experimental measurements include the use of infrared camera for surface temperature measurements, marker chemicals for time-temperature history effects, and power absorptions obtained indirectly from rate of temperature rise.; Heating pattern changes significantly with shape, size and dielectric properties of the food and its placement in the oven. Even more importantly, the heating pattern changes qualitatively with time, due to changes in properties with temperature. Thus, temperatures monitored at a few locations often may not be representative of the overall heating patterns in microwave oven heating. Only comprehensive modeling and/or appropriate experimentation can provide a complete picture. This is critical in applications involving food safety, such as sterilization.; Coupled solutions of electromagnetics and heat transfer are found necessary when dielectric properties increase significantly with temperature, as in meats. In applications such as sterilization, where large changes in temperature are needed, coupled models are necessary.; Heating non-uniformities due to the effect of focusing of the microwaves incident on a curved surface were studied for spheres and cylinders. Criterion for focusing was developed that includes wavelength of the microwaves in food, in addition to properties and size. Also, results from plane wave heating are shown to be applicable to cavity heating.; Power absorption in materials showed strong dependence on its volume and properties. When two materials of different properties are heated simultaneously, their relative power absorption follows the same trend as when heated separately. |
