Abstract
Microwave heating of solid stack materials is common but bothered by problems of uneven heating and electric discharge phenomena. In this paper, a method introducing fluid materials with different relative permittivity is proposed to improve the heating uniformity and safety of solid stack materials. Simulations have been computed based on the finite element method (FEM) and validated by experiments. Simulation results show that the introducing of fluid materials with proper relative permittivity does improve the heating uniformity and safety. Fluid materials with the larger real part of relative permittivity could obviously lower the maximum modulus value of the electric field for about 23 times, and will lower the coefficient of variation (COV) in general, although in small ranges that it has fluctuated. Fluid materials with the larger imaginary part of relative permittivity, in a range from 0 to 0.3, can make a more efficient heating and it could lower the maximum modulus value of the electric field by 34 to 55% on the whole studied range. However, the larger imaginary part of relative permittivity will cause worse heating uniformity as the COV rises by 246.9% in the same process. The computed results are discussed and methods to reach uniform and safe heating through introducing fluid materials with proper relative permittivity are proposed.
Highlights
Unlike traditional heating methods that heat materials by radiation, convection and conduction, microwaves heat materials through the direct interaction with the inner polar molecules and charged particles of materials [1]
There are some natural drawbacks of microwave heating: (a) When heating materials by microwave, there exist “hot spots” and thermal runaway problems in the system temperature [7], which will cause degradation of the processing materials [8,9,10,11] and even cause burning and explosion of the microwave reactor and reactants [12,13]. (b) When dealing with numerous solid materials, their stacking in the heating cavity can result in some sharp edges, tips or submicroscopic irregularities, which may lead to electric sparks or electric arcs [14,15]
The silicon carbide spheres are placed in a two-layer structure as shown in
Summary
Unlike traditional heating methods that heat materials by radiation, convection and conduction, microwaves heat materials through the direct interaction with the inner polar molecules and charged particles of materials [1]. (b) When dealing with numerous solid materials, their stacking in the heating cavity can result in some sharp edges, tips or submicroscopic irregularities, which may lead to electric sparks or electric arcs [14,15]. These electric discharges will affect the heating process and the product composition, and lead to safety problems when dealing with materials that have a low flashing point or in high temperature conditions [16,17].
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