OPTIMAL NUMBER OF STIRRINGS IN RADIO FREQUENCY TREATMENTS FOR IN-SHELL WALNUTS TO ASSURE INSECT MORTALITY CONTROL QUALITY

摘要

Due to orientation and location variation of in-shell walnuts during treatment, nonuniform heating is a major problem in developing a large-scale RF treatment for postharvest phytosanitary and quarantine regulations in international trade. Experiments show that rise in standard deviation of walnut temperatures increases linearly with the rise in mean temperature. This ratio, defined as uniformity index, depends on the design of an RF unit and can significantly influence the heating temperature uniformity. One possible solution is to design a serial RF system with intermittent stirring units placed in-between. For any combination of target mean temperature and desired insect mortality rate, a mathematical model is developed to determine the optimal number of RF and intermittent stirring units. This model is validated by experiments to be highly accurate.