The use of numerical simulation as a cognitive tool for studying the microwave drying of softwood in an over-sized waveguide

A previously developed mathematical model, which uses a comprehensive two-dimensional heat and mass transport code coupled with a three-dimensional code for resolving Maxwell's equations in the time domain, will be used to investigate numerous aspects of the microwave enhanced convective drying of softwood in an over-sized waveguide. At first, in order to highlight the predictive capabilities of the developed model, comparisons will be made between theory and experiment for spruce heartwood. It will be shown that the model is able to identify most of the important heat and mass transfer phenomena that arise throughout the drying process. After validation of the numerical simulation results, the work focuses on using the model as a cognitive tool for investigating important issues for closed microwave systems which include the effect of varying the sample dimensions and changing the location of the material within the applicator. Finally, a study will be presented that compares the overall drying kinetics generated within two different types of applicator designs. The first design uses a wave-trap located at the end of the waveguide to prevent reflected energy from back-propagating into the over-sized section of the guide, while the second design uses a short-circuit plane to ensure that this reflected energy is back – propagated towards the material. The advantages and disadvantages of these two designs will be deliberated. Received 25 May 1997