Modeling Radio Frequency Assisted Hot Water Heating of Fruits

摘要

Radio frequency (RF) heating of spherical fruits was modeled for a system in which fruits were moving and rotating on their axes in a water bath placed between two RF electrodes. The simulated transient temperature profile of fruits was obtained by solving Fourier's transient heat transfer equation containing internal heat generation source. The internal heat generation rate was numerically determined from the electric field inside a spherical object by solving Maxwell equations using Mie theory. The rotational behavior of fruit was taken into consideration and appropriate modifications were incorporated in calculation of power density inside the fruit. The predicted temperature profiles were obtained by using an infrared imaging camera. The mean temperature difference between experiment and simulation was 1.35 and 3.56℃ for orange and apple, respectively, after RF heating from 21℃ to above 50℃. The model was used to determine salt concentration required in an effort to eliminate differential heating of fruits between the surface and the core. The determined value of salt concentration was 0.007% for orange and 0.025% for apple, which were also in agreement with experimental values of salt concentration. However, for red delicious apples the model was not less accurate because of non-spherical shape. The developed model can be used for assessment of thermal treatment adequacy for control of insect-pests of spherical fresh fruits and design of industrial RF heating process.