Determination of the temperature distributions in a paddy rice bed during heat treatment with microwaves

During dielectric heating the electric field distribution inside a cavity occurs as from a multimodal propagation caused by countless reflections coming from the metallic walls of the cavity. These multiple reflections generate regions of greater and lesser intensities of the electric field in the space and, as a consequence, non-uniform product heating. The objective of this study was to determine the temperatures obtained during the microwave treatment of a moist paddy rice bed placed in a sample container inside the application cavity. The cavity had a prismatic geometry with a hexagonal section and was designed such that when operating at 700 W and 5.8 GHz it minimized the heterogeneity of the distribution of the electric field intensities, so as to generate a more uniform product heating. The differences registered by the sensors in the paddy rice bed ranged from 3.2 to 12.5 °C during the thermal treatments studied. No standard behaviour was observed indicating a region with more intense heating with respect to the height and radial directions inside the moist paddy rice bed in the sample container in the prismatic cavity.

Microwaves; Electric field; Temperature difference; Paddy rice