Role of metallic and ceramic supports on enhanced microwave heating processes

Abstract

Analysis has been carried out to study efficient heating due to microwaves (MWs) for the samples placed on metallic and ceramic supports ( Al 2 O 3 , SiC). The analysis is carried out for water which exhibits greater dielectric loss and oil which possesses small dielectric loss. A preliminary analysis on enhanced MW heating of samples has been carried out via average power within a sample vs. sample thickness diagram for various cases. The maxima in power, also termed as ‘resonances’ are observed for specific sample thicknesses and the two consecutive maxima in average power are termed as R 1 and R 2 modes. During both R 1 and R 2 modes, the greater intensity of resonances for power absorption in samples occurs in presence of metallic support. For a specific resonance mode in water samples, the maxima with metallic supports correspond to smaller sample thickness only. In contrast, for oil samples, the metallic support corresponds to greater average power for all sample thicknesses ( > 1 cm). Ceramic supports correspond to lower average power and Al 2 O 3 is a suitable support for water whereas SiC support may cause local runaway heating for oil sample. The spatial distributions of power illustrate that the regime connected with the metallic support is heated at a lower rate specially for oil samples. The efficient and enhanced heating strategy is further exercised with metallic–ceramic composite supports. It is observed that Al 2 O 3 –metallic for water and SiC–metallic for oil are optimal support assemblies for efficient heating. In addition, the optimal SiC–metallic support would avoid the local runaway heating of oil samples. The choice of support may not be trivial due to complex dielectric response of sample–support assembly. Our analysis is carried out for two limiting cases due to water and oil, and we have recommended efficient heating strategy for both water and oil. The heating strategy can be suitably extended for heating of any materials on a support in custom MW ovens.