Estimation of temperature profile at Ohmic heating by finite element method

The heating process of foods, in general, depends on the heat transfer such as heat conduction, heat convection and thermal radiation that are derived by the temperature difference between foods and that sources. The homogeneous and quick heating of foods is not expectable for these heat transfers because of the poor heat transfer coefficient of foods and the avoidance of overcooking on the food surface. On the other hand, the Ohmic heating will depend its heating on the generated heat when the electricity passes through the foods. According to its principle, the homogeneity of foods will result in the homogeneous and quick heating. However, it is often observed that a homogeneous paste food such as ''Miso'', fermented soybean food, show the bigger temperature deviation than expected between its center and outer surface even under the consideration of its heat diffusion. In this paper, Mise was used and measured its temperature change at 5 mm intervals from the center to the surface during the Ohmic heating at 20 kHz of alternating current. Finite Element Method (FEM) was examined to the mathematical corresponding model to the obtained temperature changes. The model that the electric conductance of Mise was changeable depending on the temperature and the voltage drop was changeable depending on the electric conductance showed good agreement with the actual result of temperature changes. The model also indicated that the crosswise temperature change of Mise to the applied electrical field, was enhanced and the longwise one was suppressed as its Ohmic heating progressed. The model will be very effective to design the electrode for Ohmic heating to achieve the real homogeneous and quick heating of foods.