A coupled electromagnetic and heat transfer finite-element model for simulating microwave processing of composite materials in a cylindrical resonant cavity

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Virginia Polytechnic Institute and State University

A coupled electromagnetic/heat transfer model capable of simulating microwave processing of composite materials in a cylindrical resonant cavity was developed. The two-dimensional model simulates processing of axisymmetric material loads in cylindrical resonant cavities operating in the TM₀₁₀ mode. The model consists of an electromagnetic model and a heat transfer model which are coupled by the heat generation term in the heat transfer equation. Heat generation in the process material is due to dielectric loss in the material and is related to the dielectric loss factor ofthe material, the processing frequency, and the magnitude of the electric field. The finite-element method was used to develop both the electromagnetic and heat transfer models. The electromagnetic model, based on Maxwell's equations, allows anisotropic conductivity and permittivity and accounts for resonance. A novel technique for determining resonance was developed for use in the electromagnetic model. The technique can be used to design microwave applicator/material systems. The heat transfer model allows anisotropic thermal conductivity and can be used to simulate heating by microwaves only, by convection only, or by a combination of microwaves and convection. The coupled model can account for the temperature dependence of dielectric properties. The electromagnetic and heat transfer models were verified by comparison to cases for which analytical solutions were available. The coupled model was then used to simulate microwave processing of nylon 66 and composite specimens of S-glass/polycarbonate. Microwave and convective heating were used alone and in combination to heat a thick cylinder of material. Comparisons are made between microwave, convective, and combined processes and the advantages and disadvantages of microwave processing are discussed.