MICROWAVE THAWING OF LOSSY DIELECTRIC MATERIALS

Abstract

Microwave thawing of lossy dielectric materials was examined theoretically. A “temperature” approach was used to model the microwave thawing of frozen slabs composed of beef or water and multilayer beef/water slabs. The heat conduction equation and Stefan equation were solved using a finite element front-tracking method and Newton iteration. The microwave power deposition in the slab was determined by an analytical solution to Maxwell's equations. Solutions to the governing equations provided transient temperature and power deposition profiles, and the position of the phase-change interface with respect to time. Dirichlet (essential) and Robin (convection) boundary conditions were investigated and thawing times were calculated for incident power levels up to 2·5 × 10⁴ Wm⁻² and slab thicknesses of 5, 10 and 15 cm. The beef samples thawed more quickly and for all situations there was less of a change in the thawing time as the power increased above 5000 Wm⁻². The thawing time versus sample thickness was found to follow a power law relationship. Thus, given a material's thawing time at a specified incident power, it is possible to estimate the thawing time for different sample thicknesses. In the absence of microwaves, the power law exponent is 2 in the case of the Dirichlet boundary condition. This value decreases below 2 upon microwave illumination.