Investigation of radio frequency heating uniformity of wheat kernels by using the developed computer simulation model

To explore the potential of using radio frequency (RF) energy to control insects or microorganisms in low-moisture granular food crops, wheat kernels were selected as a sample product, and a computer simulation model was developed to study the influence of sample size (wheat kernels filled in plastic container in cuboid shape) and vertical position on RF heating uniformity and to determine the cold and hot spots in the samples. The simulated temperature profile of RF heating was compared with the experimental results to validate the computer model. Temperature uniformity index (TUI) was selected as a criterion to evaluate RF heating uniformity. Results suggested that temperature uniformity of sample depended on sample size and location, where for small sample size, sample placed on either bottom electrode or closed to top electrode would achieve better RF heating uniformity: while for sample in large size, placed in the middle or slightly lower than middle position between the two parallel electrodes achieved better temperature uniformity. Also, a larger sample size had better RF heating uniformity, especially when sample size equaled to the size of the top electrode, indicating that RF energy is more suitable for treating bulk materials. Corner heating was also observed where hot spots located at the corner of samples in cuboid shape, and cold spots depended on sample vertical position. In this study, cold spots were at the center of the top and bottom layers when the sample was placed at the middle position between the two parallel electrodes, at the center of top layer when sample was placed on the bottom electrode, and at the center of bottom layer when sample was placed close to top electrode. Information generated from this study would be essential for developing RF treatment protocol to control insects or microorganisms in low-moisture granular agricultural products. (C) 2015 Elsevier Ltd. All rights reserved.