Sensitivity analysis of container properties to heating uniformity of soybeans during radio frequency treatment

Abstract

Radio frequency (RF) treatment has been proved to be effective in disinfestation and pasteurization. However, inhomogeneous heating is still the main issue for RF treatment to be applied in large-scale processing industry. In this study, a finite element model was built to analyze the sensitivity of container properties (dielectric constant, loss factor, thermal conductivity, density, heat capacity, and resistivity) to the RF heating uniformity of soybeans in pilot-scale systems and the established model was validated by the experiments, which were conducted by a 6 kW, 27.12 MHz RF system. Temperature profiles of the sample predicted from the model matched the experimented results well because the maximum relative percent error was less than 10 %. The sensitivity indexes of dielectric constant, loss factor, thermal conductivity, density, heat capacity, and resistivity changed from 0.254, 0, 0.059, 0.015, 0.015, and 0, to 0.292, 0, 0.004, 0.151, 0.151, and 0, respectively, when the thickness of the container increased from 2 mm to 5 mm. Since the dielectric constant determines the electric field distribution in sample during RF treatment, it was the most sensitive property in affecting RF heating uniformity of soybeans, followed by the thermal conductivity, density, and heat capacity of the specific container. Loss factor and resistivity of the container had less effect on the RF heating uniformity of sample. These results may provide a theoretical basis for the selection of appropriate container materials to improve RF heating uniformity and promote its applications in large-scale processing industry.