Improving microwave heating uniformity of spherical objects by wrapping optimized dielectrics

As a green and efficient heating technology, microwave heating has shown its superiority in many fields. However, hot spots widely exist when heating spherical objects which may lead to overheated damages. In this work, a method of designing dielectrics for wrapping spherical objects is proposed to reduce hot spots in microwave heating. Firstly, a comprehensive model based on the geometrical optics is proposed to analyze the hot spot formation in the spherical object. Secondly, a multi-physics model based on the finite element method is built to simulate the heating process of the spherical object wrapped by the dielectric in an electrically large cavity with moving elements. The optimal shape and relative permittivity of the dielectric are determined by the simulations. Finally, a cuboid alumina ceramic with a dimension of 70 mm x 80 mm x 150 mm and a relative permittivity of 9.2 is customized according to the simulation results to wrap the spherical object. The experiment results measured in a practical microwave heating system are in good agreement with the simulation results. Both the simulation and experiment show that the proposed method can efficiently reduce the hot spot and significantly improve the heating uniformity.