Introduction: Dielectric Heating Is a Widely Used Electromagnetic Heating Technology. Vibrational Energy (Heat) Is Induced in Th
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Modeling Dielectric Heating: A First Principles Approach R. W. Pryor, Ph.D. Pryor Knowledge Systems, Inc., Bloomfield Hills, MI, USA Introduction: Dielectric heating is a widely The model uses the Electric Currents used electromagnetic heating technology. (ec) and the Heat Transfer in Solids (ht) Vibrational energy (heat) is induced in the Modules to determine the voltage material by the application of an RF field. needed to heat the whey gel to the This model explores the physical effects pasteurization range (71.7 C for 15 when different frequencies within the sec.). Solving this model required a internationally allocated bands[1] are utilized two-step process: 1) Electric currents to pasteurize whey gel (≈gelled milk) in order using the Frequency domain solver and to determine the most efficient parameters. 2) Heat transfer using the Stationary Solver. Table 1 and Figure 4 show the resulting voltage values and fit curve. Figure 1. Whey gel pasteurization channels ’ Figure 2. Permittivity Figure 3. Permittivity Imag- Computational Methods: A material s Real Data and Fit Curve inary Data and Fit Curve electronic heating behavior is represented by its relative permittivity (dielectric constant), i.e. the difference between the material ’ s permittivity relative to that of free space, a fundamental constant whose value is: Table 1. Input Voltage to Figure 4. Input Voltage vs. The permittivity of a material is: Reach Pasteurization T Frequency at a constant T For complex materials that have intrinsic phase delays and energy losses, the relative Conclusions: The results confirm that in permittivity is represented by a complex materials with a large volumetric fraction of number, such as: water, the required input voltage decreases as a function of frequency. The As whey gel is essentially water, the basic modeling process also demonstrated that physical properties of water from the the results are sensitive to the specific COMSOL Multiphysics Materials Library were behavior of the material being modeled. modified by adding the measured complex permittivity values for whey gel [2]. Figures 2 References: and 3 show the power series polynomial 1. Radio Regulations, ITU-R (2012). curves generated by the author from the 2. Yifen Wang, et al., J. Food Eng., 57, measured permittivity at four individual 257-268 (2003). frequencies. Excerpt from the Proceedings of the 2015 COMSOL Conference in Boston.