Optimization of continuous-flow microwave processing with static mixers for enhanced heating uniformity

Abstract

This study addresses the challenge of non-uniform heating in continuous-flow microwave processing of highly viscous liquid foods, a common issue that leads to the formation of hot and cold spots in the food product, leading to reduced product quality. Non-uniform heating is especially problematic for viscous fluids due to their low viscosity, which hinders heat transfer. The objective of this study is to investigate the use of a Kenics static mixer – a device consisting of alternating counterclockwise and clockwise twisted helical elements – designed to improve heat mixing and enhance temperature uniformity in such systems. The Kenics mixer is particularly suitable for handling highly viscous fluids, where effective mixing is critical for achieving uniform temperature profiles. To evaluate the performance of the Kenics static mixer, a numerical model of the continuous-flow microwave processing system equipped with Kenics mixer was developed. The model simulates fluid flow, heat transfer, and electric field distribution within the system using the finite element method. A genetic algorithm was used to optimize the system, with temperature uniformity (quantified by the coefficient of variation in fluid temperature at the outlet) as the objective function. The study explores two Kenics mixer configurations: R-L and R-R, and examines the effects of Kenics mixer design (aspect ratio, thickness, gap between Kenics mixers, and number of Kenics mixers) and fluid velocity on temperature uniformity at the fluid outlet. The results show a 71.04 % and 72.09 % improvement in temperature uniformity at the fluid outlet for the R-L and R-R configurations, respectively, compared to that of a hollow pipe. The R-R configuration also achieved a higher mean outlet temperature without sacrificing temperature uniformity at the fluid outlet. Using lossy materials for Kenics mixer reduces the temperature uniformity at the fluid outlet while increasing mean fluid outlet temperature for both configurations. The study concludes that incorporating the Kenics static mixer can significantly reduce non-uniform heating in continuous-flow microwave processing, enhancing the efficiency and scalability of food processing systems for viscous fluids.