Application of numerical simulation techniques for modeling pulsed electric field processing

Abstract

The application of numerical simulation techniques is becoming more and more popular with the progress of computational capabilities. It finds use in the context of pulsed electric field (PEF) research in various ways, especially to predict treatment efficacy and homogeneity. This contribution aims to be an orientation guideline for numerical investigations. It provides a mathematical framework as well as an understanding of the interrelations of fluid dynamic, thermal, and electric fields that are important to investigate PEF processes. Emphasis is put on the versatility of numerical models: modeling of permeabilization and inactivation of enzymes and spoiling agents, prediction of treatment homogeneity, modeling of particulate fluids, modeling of microscopic aspects of the permeabilization process, and geometry and process optimization are described exemplary for the broad range of possible applications to motivate novel approaches. The presented theory is used for a case study: the flow fields, temperature fields, and electric field strengths are simulated for three different coaxial treatment chamber geometries. They vary in the shape of the central insulator. The geometry with an arc-shaped insulator provides the highest treatment intensity with regard to the electric field strength and treatment times but also has the largest coefficient of variation of the electric field strength in the treatment area. The results suggest that a trade-off between treatment effect and homogeneity is necessary. However, the fields can be used to compute the residual activity of the enzyme pectinesterase (PE) with a balance equation in a second simulation. A sink term in the balance equation is used to couple in the effect the treatment has on the enzyme to predict its inactivation spatially. The approach offers a more quantitative basis for process evaluation. Comparing the residual activities, the arc insulator indeed provides the largest treatment effect. It also reveals that the differences in treatment homogeneity are smaller than the electric field strength distributions suggest. Balancing the residual activity increases the conclusiveness of the numerical investigation.