Theoretical analysis on efficient microwave heating of materials with various square cross sections in the presence of lateral and radial irradiation

A theoretical analysis has been carried out to analyse the efficient heating process of long rectangular samples with various orientations of square cross sections in the presence of lateral and radial irradiation. Lateral irradiation represents the sample incident at one direction with the source at infinity whereas radial irradiation represents the situation where the sample is incident with microwave radiation from the coaxial cylindrical cavity at infinity. Electric field equations have been solved with a hypothetical circular domain which surrounds the square cross sections and facilitates the solution of field equations with the radiation boundary condition. The electric field and temperature have been solved using the finite element method for the composite domain. Generalized characteristics on power absorption and temperature distribution as functions of the wave number (Nw) and the penetration number (Np) have been obtained. Radial irradiation gives a larger power absorption for Nw ≤ 0.56 and either lateral or radial irradiation is favoured for Nw ≥ 0.56 based on various Np values. The aligned square cross section is found to give larger heating rates in the presence of dominant lateral irradiation. The detailed spatial distributions of power and temperature are extensively studied and the suitability of either radial or lateral irradiation for a specific cross section has been recommended. The large heating rate as well as minimal thermal runaway become the competing factors for the selection of a specific heating strategy. The case studies are demonstrated for high and low lossy substances (beef and bread)