15D-28 |
A computer simulation of heating uniformity in a pressurized RF sterilization and pasteurization system |
Y. WANG1, T. D. Wig1, J. Tang1, and L. M. Hallberg2. (1) Dept. of Biological Systems Engineering, Washington State Univ., 213 L.J. Smith Hall, PO Box 646120, Pullman, WA 99164-6120, (2) Combat Feeding Program/ Soldier Systems Center, U.S. Army Soldier & Biological Chemical Command, Advanced Processing and Packaging Team, Kansas St., Natick, MA 01760-5018 Dielectric heating can overcome the limits of uneven and slow heating inherent in conventional retorting. Electromagnetic energy in the radio frequency (RF) range has long penetration depths in foods and can volumetrically heat institutional size food packages. Dielectric loss factors of foods in the RF range often increase with temperature, which may cause localized thermal run-away. It is therefore crucial that RF systems are properly designed to provide uniform electric fields in the treated foods during pasteurization or sterilization. The goal of this work was to use electromagnetic modeling to aid in the design of an RF heating apparatus and pressure vessel to impose a uniform energy distribution in a packaged product in pasteurization and sterilization processes. Dielectric properties of selected foods were measured in the RF range using an impedance analyzer and an open-ended coaxial probe. The Finite-Difference Time-Domain (FDTD) method was used to simulate electric field intensity and specific absorption rates in a pilot-scale pressured RF sterilization system developed at Washington State University. These data were used to predict the effects of modifications to the system and pressure vessel on heating uniformity and to determine areas that might be prone to arcing. Chemical markers and fiber-optic temperature sensors were employed to measure the heating effect imparted to a large package of model food. Simulation results led to improved designs of both the tuning structures and the pressure vessel. Chemical marker yields and measured temperatures confirmed that a very uniform field can be applied to a packaged model food. The results of this work suggest that computer simulation can be a suitable tool for studying thermal treatments of packaged foods in pressurized RF sterilization systems. Modeling software may be of further use in improving the design of RF compatible packages and processes.
Session 15D, Food Engineering: Processing Technologies
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