A Numerical Investigation of Combined Microwave and Convective Drying of a Hygroscopic Porous Material: A Study Based on Pine Wood

Abstract

In this paper a numerical investigation of the combined microwave and convective drying of a hygroscopic porous material is undertaken. A comprehensive mathematical model has been developed and a numerical code known as Wood1 D implemented so that the impact of dielectric heating on the overall drying kinetics can be analysed. The code, which provides the analysis of the time evolution of moisture content, temperature, pressure and microwave power distributions, is an effective tool which can be used to obtain a better understanding of the underlying physics of the drying process at a fundamental level. Furthermore, the simulations can be used to identify key model parameters so that a subsequent sensitivity study can be carried out in order to establish the effects that these parameters have on the performance of combined microwave and convective drying. Once the model has been fine tuned to the drying engineer's specifications, the code can be used to assist with the optimization of a given dryer design. In this work the model is tested and validated against experimental data for both convective drying and combined microwave and convective drying of pine wood. The drying times, drying rates and efficiencies, together with the related moisture, temperature, pressure and power profiles will be compared and analysed for a number of combinations of convective and microwave energy. It is hoped that the knowledge gained from this study can be used to assist with the evaluation of the overall economic feasibility of using combined microwave and convective drying processes.