09:45
Modeling of microwave and RF power applications (1)
09:45
15 mins
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Mild pasteurisation of packaged foods with Water immersed radio-frequency heating
Erik Esveld, Rian Timmermans, Ariette Matser
Abstract: Conventional pasteurisation of packed foods in an autoclaves requires a long time to reach a sufficient temperature in the centre. With RF pasteurisation, the time at high temperature (> 72°C) is significantly reduced with respect to conventional autoclave processing, while achieving the same microbial stability for the product. The result is that the colour, texture and taste of the vegetables in ready-to-heat meals is minimally affected and kept during prolonged chilled retail.
The homogeneity of heating that must be achieved with immersed RF technology is crucial. This was achieved with the aid of a hot water surrounding during the radio-frequency heating and a careful balancing of the displacement currents. The non-conducting water surrounding does not absorb the RF energy, but instead increases the efficiency and robustness of the process. It ensures both a minimal thermal treatment everywhere and prevents over processing of the outside and corners.
As the maximum internal temperatures stays well below the boiling point, the hermitically sealed packages can be pasteurised under ambient pressure conditions without the need of a vent.
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10:00
15 mins
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SEMI-ANALYTICAL MODEL FOR NON-UNIFORM MICROWAVE HEATING OPTIMIZATION IN A 1-D MULTI-MODE CAVITY
Eli Jerby
Abstract: A semi-analytical model for microwave heating in a 1-D multi longitudinal-mode cavity [1] is further developed and implemented in this study. The current source region is separated here from the non-uniform dielectric load, and no symmetry is presumed. A transfer-matrix equation, derived in the frequency domain for the electromagnetic radiation pattern evolved in the cavity, is coupled to the heat equation in a two-time-scale approximation [2]. This model demonstrates effects of non-uniform heating, temperature-dependent parameters, thermal-runaway instability, and hotspot formation in the cavity. For a variable frequency excitation (e.g. by a solid-state microwave generator), this model enables feasibility studies of real-time process-control strategies, including impedance matching by frequency tuning, power spreading and electronic turn-table-like features, and various optimization techniques.
References
1. Jerby E., Chem. Eng. Proc., In Press, https://doi.org/10.1016/j.cep.2017.02.008.
2. Jerby E., O. Aktushev, V. Dikhtyar, J. Appl. Phys., 2005, 97, 034909.
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10:15
15 mins
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MODE STIRRER BASED ON MULTI-MATERIAL TURNTABLE FOR MICROWAVE HEATING
Jinghua Ye, Huacheng Zhu, Kama Huang
Abstract: Microwave non-uniform heating has been a main drawback of the microwave heating, many methods were proposal to solve the non-uniformity heating[1]. In this paper, a novel multi-material turntable structure is creatively proposed to improve the temperature uniformity in microwave ovens. Polyethylene (PE) and alumina are selected as the material composition of turntable. During the heating process, the processed material is placed on a fixed Teflon bracket which is over the constantly rotating turntable. By using COMSOL Multiphysics, we built the multi-physics models and simulated the heating process with a constantly rotating multi-material turntable. From Fig.1, we can clearly see that the electric field distribution in the microwave oven vary significantly with time, because of the rotation of the multi-material turntable. The position of a strong electric field at a certain moment is likely to shift largely at the very next moment. The coefficient of variation (COV), calculated as the ratio of the standard deviation to the mean, is adopted to quantify the non-uniformity of temperature in different heating process, as shown in Table 1. Table 1 shows that the multi-material turntable can improve the heating efficiency (up to 113%) and the heating uniformity (up to 51%) effectively.
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