Microwave-assisted drying of composite materials: Modelling and experimental validation.

摘要

Model materials with discretely varying loss factors under microwave fields, were studied with respect to drying characteristics. In the first part numerical simulations were conducted to study the fluid flow and heat transfer in a rectangular microwave cavity where cylindrical samples were heated by microwave. The Reynolds numbers studied in this work were 2800, 5600 and 11200 based on the entrance diameter to the rectangular microwave cavity. Heat transfer results in terms of Nusselt numbers for the Reynolds number ranges studied are presented and discussed.; In the second part of the study a mathematical model was developed to describe heat and mass transfer of a model material under microwave fields. The dynamic temperature and moisture profiles of cylindrical composite samples subjected to microwave and convective energy were determined and validated at microwave power density levels of 0.20 W/g, 0.3 W/g and 0.4 W/g based on initial weight of the sample. Model results were compared with experimental data and found to agree within 1.0–2.6%. Predicted temperature profiles at selected locations within the model material were also showed a good agreement with experimental data. However, a significant discrepancy between the numerical and experimental temperature results occurred after t > 30 minutes. This might have been due to localized overheating, or to mathematical model overestimation.; Lastly, a quality evaluation of the dried samples was also performed. Quality attributes evaluated were surface color, shrinkage and rehydration capacity. Samples dried as a special case of biological material were of better quality when compared to other samples.