The effect of modifying the geometrical configuration of a co-linear chamber to improve its performance and to increase the microbial inactivation was investigated numerically and validated experimentally. In non-thermal radio frequency electric fields (RFEF) processing, co-linear chambers exhibit low tendency to dielectric breakdown and arcing, especially in liquid food products with high electrical conductivities, but they show low energy efficiency and poor uniformity of processing conditions. Accordingly, a standard co-linear chamber (C1) with 1 mm of length and 3 mm of diameter was selected. The chamber included a gap between the end of electrodes and the treatment zone, as well as a diameter contraction at that zone. The geometry of the standard co-linear chamber was modified by removing the recirculation/stagnation zones adding stainless steel tubes (C2), as well as through the additional insertion of stainless steel mesh to contain the electric field within the treatment zone (C3). These configurations were evaluated numerically using COMSOL Multiphysics modelling. The model was validated by comparing experimental measurements of outlet temperature and power consumption with the model predictions. The numerical study showed that C3 exhibited a more uniformly distributed electric field and temperature profiles as well as higher velocities and turbulent kinetic energy that were also more evenly distributed within the treatment zone, compared to other configurations. In experimental studies, C3 achieved the highest microbial inactivation at constant values of peak voltage, electric field strength, and energy levels. Furthermore, C3 showed the most energy efficiency among the three geometrical configurations.

Industrial relevance

As an alternative to thermal processing, radio frequency electric fields (RFEF) processing needs to ensure the microbial safety of the food products in an energy-efficient manner due to the challenges on controlling Joule heating, which can lead to arcing and the dielectric breakdown of the treatment chamber. This can be achieved by designing treatment chambers that can enclose the electric field within the treatment zone while providing a more evenly distributed electric field, hydrodynamic and temperature profiles within that zone. This study proves that the geometrical configuration of co-linear chambers can be altered to minimize the energy consumption while maximizing the microbial inactivation. The findings can be used for scaling up and advancing the industrial application of RFEF technology for food processing.

中文翻译：

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几何修改对用于非热射频电场处理的共线腔室性能的影响：带有实验验证的数值研究

数值研究了修改共线室的几何构型以改善其性能并增加微生物灭活的效果，并进行了实验验证。在非热射频电场（RFEF）处理中，共线腔室显示出低的电介质击穿和电弧放电趋势，特别是在具有高电导率的液体食品中，但是它们显示的能量效率低且处理条件的均匀性差。因此，选择了长度为1mm，直径为3mm的标准共线室（C1）。腔室包括电极末端和处理区域之间的间隙，以及该区域的直径收缩。通过移除添加不锈钢管的再循环/停滞区（C2），以及通过额外插入不锈钢网以将电场包含在处理区（C3）中，可以修改标准共线室的几何形状。使用COMSOL Multiphysics模型对这些配置进行了数值评估。通过将出口温度和功耗的实验测量结果与模型预测值进行比较来验证模型。数值研究表明，与其他配置相比，C3的电场和温度分布更均匀，速度和湍动能更高，在处理区域内分布更均匀。在实验研究中 C3在恒定的峰值电压，电场强度和能级值下实现了最高的微生物灭活。此外，C3在三种几何构型中显示出最高的能效。

行业相关性

作为热处理的替代方法，由于在控制焦耳加热方面存在挑战，射频电场（RFEF）处理需要以节能的方式确保食品的微生物安全，这可能导致电弧和电弧的介电击穿治疗室。这可以通过设计处理室来实现，该处理室可以在处理区内封闭电场，同时在该区内提供更均匀分布的电场，流体动力学和温度曲线。这项研究证明，可以改变共线腔室的几何构型，以在最大程度降低微生物灭活的同时最大程度地减少能耗。这些发现可用于扩大和促进RFEF技术在食品加工中的工业应用。