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An Experimental Method for Evaluating Heating Uniformity in RF Systems

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  036202,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14157) @2003
Authors:   S. Wang, J. Tang
Keywords:   Heating rate, Insect control, Radio frequency, Temperature uniformity

Temperature uniformity is one of the most important considerations for scaling up of the established treatment protocol for walnuts and for the development of the new protocols for fresh fruits. A water load was designed at WSU to determine the heating uniformity in a 12 kW, 27 MHz pilot scale RF system. A fiber-optic temperature measurement system was used to monitor temperature-time history and 24 thermocouples were used to simultaneously measure final water temperatures both in horizontal and vertical planes. Regulating the air gaps resulted in different power couplings in the water container ranged from 5.5 kW to 10 kW and corresponding heating rates of 5.3 to 9.4 C/min. The hottest spot was always located at the electrode center. The temperature difference between front and back sides was less than 2C, but the difference between right and left sides was as much as 10 C. A relative large zone in the center where the temperature difference was less than 4 C was defined. Symmetric design of inductance positions and feeding strips improved the temperature uniformity. Further research is needed to improve the temperature uniformity with the help of modeling.

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