Microwave thawing of cylinders

Microwave thawing of a cylinder is examined. The electromagnetic field is governed by Maxwell's equations, where the electrical conductivity and the thermal absorptivity are both assumed to depend on temperature. The forced heat equation governs the absorption and diffusion of heat where convective heating occurs at the surface of the cylinder, while the Stefan condition governs the position of the moving phase boundary. A semi-analytical model, which consists of ordinary differential equations, is developed using the Galerkin method. Semi-analytical solutions are found for the temperature, the electric-field amplitude in the cylinder and the position of the moving boundary. Two examples, consisting of the no heat-loss (insulated) and large heat-loss (fixed temperature) limits, are considered, and a good comparison is obtained with the numerical solution of the governing equations. The semi-analytical model is coupled with a feedback control process in order to minimise thawing times. A strategy is developed which greatly shortens the thawing time whilst avoiding thermal runaway, hence improving the efficiency of the thawing process. (C) 2004 Elsevier Inc. All rights reserved.