Coupled electromagnetic thermal and kinetic modeling for microwave processing of polymers with temperature- and cure-dependent permittivity using 3D FEM.

摘要

Polymer processing is an important application of microwave heating in industry. Microwave assisted curing of thermoset polymers has the advantage of heating the polymer precursor materials volumetrically and hence can lead to superior cure with efficiency not available with conventional convection heating. However, due to the complex interactions between the electromagnetic fields and the material, achieving the promise of microwave assisted curing is challenging. This is due to the fact that electrical properties (e.g. the complex permittivity) of the material change non-linearly with temperature and composition during the curing process. Hence, the field distribution within the cavity applicator changes as a function of the extent-of-cure and local temperature of the materials being processed. It is vital in modeling the curing process that the microwave power deposition, heat transfer, and polymer curing kinetics be coupled together.; In this work, we develop a self-consistent 3D marching-in-time multiphysics model, which includes electromagnetic field distribution, microwave power absorption, heat transfer, and polymer curing kinetics. Temperature- and cure-dependent permittivity and curing kinetics for DGEBA/DDS based on experimental data are explicitly included in the model. An edge-based finite element method (FEM) is implemented as an electromagnetic model to ensure the tangential continuity of electric field and divergence-free condition for source free region, while node-based FEM is used in thermal model to solve for the temperature distribution. The numerical results can be used to determine the time-dependent temperature distribution and curing profile across the polymer sample, as well as the electromagnetic field distribution within the cavity applicator. With the help of this numerical model, robust control strategies can be developed for the polymer curing process. The numerical results are compared with the measured data and a good agreement is achieved.; In this research, the electromagnetic modeling of a novel adaptable multi-feed multimode cylindrical cavity applicator is performed, where the spatial distribution of the electric field can be specified a priori to accomplish a desired processing task. The electric field intensity inside the cavity can be tailored by varying the power delivered to each port, and mode-switching can be realized without mechanically adjusting the cavity dimensions. An orthogonal feeding mechanism is developed to reduce the cross coupling between the ports. Numerical simulations are performed for the cavity applicator to verify the theoretical analysis.