OHMIC HEATING OF SOLID‐LIQUID MIXTURES: A COMPARISON OF MATHEMATICAL MODELS UNDER WORST‐CASE HEATING CONDITIONS¹

Abstract

A critical issue in the modeling of ohmic heating of solid-liquid mixtures is the understanding of worst-case scenarios, and in particular, the reliability of mathematical models under such conditions. This study involves examination of two alternative published formulations, one involving the use of circuit theory and a well-mixed fluid assumption, against another formulation, involving the solution to Laplace's equation, but without convective effects. As apected, the models (and an analytical solution) yield identical results under situations where solid andfluid electrical conductivity are equal. However, when the solid is of lower electrical conductivity than the fluid, the Circuit Analogy, Mixed Fluid ( C M F ) approach is shown to be more conservative than the Laplace Equation,No Convection (LENC) approach. This prediction is borne out by experimental studies, which confirm that the worst-case scenario in ohmic heating is not necessarily associated with a stationary fluid situation. Under the less likely conditions where the solid is more conductive than the fluid, the LENC approach is more conservative than the CAMF approach. Models are also compared with respect to other features, such as practicality of use, and computational cost.

Electrical conductivity of particle–fluid mixtures in ohmic heating: Measurement and simulation

“…4). Sastry and Salengke (1998) used a Circuit Analogy, Mixed Fluid (CAMF) model for a simulation study on the ohmic heating of solid-liquid mixtures. As shown in Fig.…”

“…Sastry and Palaniappan (1992) developed a three-dimensional finite element model for the ohmic heating of particle-liquid mixtures and found that the EC and volume fraction of each phase were the critical parameters affecting the heating rate. Sastry and Salengke (1998) compared two mathematical models (the Circuit Analogy, Mixed Fluid model and the Laplace Equation, No-convection model) for the ohmic heating of solid-liquid mixtures (with single particle only) under worst-case heating scenarios (solid and liquid with very different EC). Using finite element software, Fu and Hsieh (1999) performed a simulation of a two-dimensional static ohmic heating system containing one single rectangular particle.…”

Temperature dependent electrical conductivities of fruit purees during ohmic heating

“…12 and 13 different voltage gradients were applied for apricot and peach purees, respectively. Electrical conductivities of samples were calculated from voltage and current data using the following equation (Sastry & Salengke, 1998;Wang & Sastry, 1993):…”

Ohmic Heating of Liquid Whole Egg: Rheological Behaviour and Fluid Dynamics

“…Although conventional thermal pasteurisation still represents the most available and best understood technique, it may affect functional properties of egg products: the coagulation, the foaming and the emulsifying properties and the degradation of quality (Góngora-Nieto et al 2003;Hermawan et al 2004;Nolsoe and Undeland 2009). Ohmic heating is an alternative heating system for pumpable foods which is based on the passage of electrical current through a food product which serves as an electrical resistance (Reznick 1996;Sastry and Salengke 1998;Icier 2003). Ohmic heating yields better products, clearly superior in quality than those processed by conventional heating (Allali et al 2008).…”