Microwave thawing of slabs

Abstract

Microwave thawing of a semi-infinite one-dimensional slab is examined. The system is governed by the forced heat equation and Maxwell's equations. Both the electrical conductivity and the thermal absorptivity are assumed to depend on temperature. Convective and radiative heating occurs at the leading edge of the slab, while the Stefan condition governs the position of the moving phase boundary. An approximate analytical model is developed using the Galerkin method. Approximate analytical solutions are found for the temperature and the electric-field amplitude in the slab, which when combined with the Stefan condition allows the position of the moving front to be found. It is shown that the model produces accurate results in the limits of no heat-loss (insulated) and large heat-loss (fixed temperature) at the leading edge of the slab when compared with the full numerical solution for a number of different parameter choices. The approximate model is coupled with a feedback control process in order to examine and minimise slab melting times. A thawing strategy is developed which greatly shortens the thawing time whilst avoiding thermal runaway, hence improving the efficiency of the thawing process.