| As a kind of dielectric heating, radio frequency(RF) heating technology has been widely used in the field of food and agricultural product processing because of its rapid and volumetric heating, self-balance of moisture content, differential heating of insects and no chemical residue left. In the process of large-scale industrial application development, in order to overcome the non-uniform heating problem, it is significant to optimize parameters of RF system and heating process. Computer simulation technology is an important method for the research of RF heating technology because it has the advantages of convenient, fast, not limited to experimental conditions and equipment. In the process of modeling, the top electrode voltage is an important input parameter. It has a great significance for the reality of the simulation to determine the real value of the voltage and study the distribution uniformity. This paper focuses on model validation and distribution uniformity of top electrode voltage. The top electrode voltage was studied systematically, new methods and suggestions were proposed to improve the non-uniform of RF heating and promote the application of RF heating.In this paper, the following experiments were conducted: model validation on the top electrode voltage of the RF heating system and study on the distribution uniformity of the top electrode voltage. The detailed research contents were completed as follows:(1)The soybeans with three different moisture contents were heated under 5 electrode gaps, the temperature profile of 3 selected points and temperature distributions of 3 layers were obtained, the current values were recorded during the test.(2)Based on the current value, the voltage of the top electrode was calculated by the voltage estimation model.(3)The top electrode voltage estimated based on the anode current was used for the computer simulation, and the validation of the model was achieved by comparing the matching degree of the experiment and the simulation results under the same conditions.(4)The voltages of five different points on the top electrode were measured to obtained the voltage distribution and the voltage distribution was verified by experiment. The main results were described as follow:(1)Results showed that anode current(Current in radio frequency systems) decreased with increasing electrode gap, but the measured current(Current in measuring device) increased with increasing electrode gap. The voltage increased almost linearly with increasing moisture content or decreasing electrode gap. The maximum difference of the estimated top electrode voltages between the anode current and the measured current in the same conditions reached 111 V, indicating less than 10% relative error. The voltages estimated by the anode currents were applied for simulation and the voltages estimated by the measured currents could be used as reference values for comparison。(2)The temperature distributions in three representative layers from simulation were in good agreement with those from experiment, and the average and maximum root mean square error(RMSE) for temperature profiles in three selected positions were 1.6% and 3.5%, demonstrating that the voltage estimated by the model can be used for computer simulation accurately.(3)The results showed that the output voltage of the RF systems was not influenced by the copper strap shape connected to the measuring device, but increased linearly with increasing the length of the copper strap.(4)The voltages at P4 and P5 were higher than those at P2, P3, and P1. Specifically, the deviations between the minimum and the maximum values among the five voltages were 694.3 and 440.9 V, corresponding to the highest voltage difference of 11.99 and 7.12% without and with load, respectively. The average deviation of voltages over five positions between with load and without load was 6.1%. The results of the validation experiment were consistent with the above voltage distribution. |
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