Modeling of Combined Microwave and Convective Drying of Wood: Prediction of Mechanical Behavior via Internal Gas Pressure

Abstract

The impact of microwave drying on the quality of dried wood remains unclear. Particular attention should be paid in order to optimize the combined microwave and convective drying process. In this study, a comprehensive internal heat and mass transfer model was developed and numerically implemented in order to simulate and understand the physical phenomena occurring inside Jack pine wood during a combined microwave and convective drying process. The model was validated on the basis of the average moisture content curves for drying scenarios at various microwave power levels. According to the simulations results, an increase in microwave power significantly decreases the drying time of Jack pine wood and increases its internal gas pressure, which increases the risk of cracking. However, compared to purely conventional convective drying, combined microwave and convective drying at medium microwave power and air temperature significantly reduces the drying time and maintains the internal gas pressure at reasonable values. At these conditions, the risk of cracking will be diminished. This last result was checked via experimental measurements of the sample strength dried at different microwave power levels. From this study, we can consider that for Jack pine wood, combined microwave and convective drying is a more efficient technology compared to classical convective drying.

Keywords:

• Combined microwave and convective drying
• Internal gas pressure
• Jack pine wood
• Modeling and simulation
• Strength

ACKNOWLEDGMENTS

Our thanks go to Gilles Villeneuve, from the University of Quebec in Abitibi-Témiscamingue, and Abderrazak Zaaraoui, from the University of Tunis El Manar, for their technical assistance and help in carrying out the experiments.