Modeling of radio frequency heating of packed fluid foods moving on a conveyor belt: A case study for tomato puree

Abstract

Computer simulation models were used to study radiofrequency heating of liquid foods moving on a conveyor belt between staggered-through field electrodes of non-uniform electric field distribution. Voltage across the electrodes was estimated using a finite-element model and a one-dimensional model, and these were utilized to simulate heating of tomato puree mixtures of varying dielectric and thermal properties, at various nominal voltages and electrode gaps. The experimental results for volume average temperatures showed good agreement with the outcome of both simulation models. Although the temperature profiles indicate a concentration of heat at the bottom and edges of the bottle, natural convection and the shape of the container helped mitigate heat localization. It was determined that, while simple models could provide accurate volume average temperatures, incorporating convectively enhanced conductivity was necessary to accurately predict temperature distribution. The heating rate was found to decrease with an increase in salt concentration. Industrial relevanceIn-package tunnel pasteurization is preferred over continuous-flow pasteurization for certain commercial products such as carbonated beverages or semi-solid foods of high viscosity. Dielectric heating can be applied in these cases with much lower requirements of floor space, water, and energy, while reducing heat losses and localized overheating. However, the radiofrequency heating of liquid foods has not been extensively studied, especially for in-package thermal treatments. A better understanding of the effect of various processing parameters on temperature distribution and heating rates could support a wider adoption of this technology in industrial processes.