Theoretical analysis on microwave heating of oil–water emulsions supported on ceramic, metallic or composite plates

Abstract

A detailed theoretical analysis has been carried out to study efficient heating due to microwaves for one-dimensional (1D) oil–water emulsion samples placed on various ceramic, metallic (reflective) and ceramic–metallic composite supports. Two typical emulsion systems are considered such as oil-in-water (o/w) and water-in-oil (w/o). A preliminary study has been carried out via average power vs emulsion thickness diagram to estimate microwave power absorption within emulsion samples for various cases. The maxima in average power, also termed as ‘resonances’, are observed for specific emulsion thicknesses and the two consecutive resonances of significant magnitudes are termed as R 1 and R 2 modes. For both o/w and w/o emulsions, it is observed that microwave power absorption is enhanced in presence of metallic and composite supports during both R 1 and R 2 modes. The efficient heating strategies characterized by ‘large heating rates’ with ‘minimal thermal runaway’ i.e. uniform temperature distributions within the sample have been assessed for each type of emulsion. Based on the detailed spatial distributions of power and temperature for various cases, SiC-metallic composite support may be recommended as an optimal heating strategy for o/w samples with higher oil fractions ( ϕ ⩾ 0.45 ) whereas metallic and Alumina-metallic composite supports may be favored for samples with smaller oil fractions ( ϕ = 0.3 ) during R 1 mode. For w/o samples, SiC-metallic composite support may be suitable heating strategy for all ranges of water fractions during R 1 mode. During R 2 mode, metallic and Alumina-metallic composite supports are favored for both o/w and w/o emulsion samples. Current study recommends the efficient way to use microwaves in a single mode waveguide and the heating strategy can be suitably extended for heating of any other emulsions for which dielectric properties are easily measurable or available in the literature.