Theoretical study of microwave heating patterns on batch fluidized bed drying of porous material

Abstract

The effects of microwave heating patterns were investigated for the case of batch fluidized bed drying by solving numerically a coupled heat and mass transfer model. Three patterns, uniform, sinusoidal and rectangular waves, were examined with the average electric field strength kept constant at 1000 V/m. Properties of apple were used to represent porous materials. The results show that the magnitude and distribution of the moisture, temperature and pressure within a particle can be significantly affected. More importantly, the drying time and microwave energy consumption change with the pattern of how microwave heating is applied. Particularly, intermittent heating with a rectangular wave pattern has the most microwave energy consumption but the shortest drying time. For a particle size of 5 mm, airflow rate of 2 m/s and temperature of 60°C, the bed area factor fA of 100, the drying time is, respectively, 1600, 2000, 2400 s for rectangular, sinusoidal, and constant microwave heating. The values of microwave energy consumed for the three cases are, respectively, 2145, 1980, and 1560 kJ/kg water evaporated. © 2001 Published by Elsevier Science Ltd.