Food processes must ensure safety and high-quality products for a growing demand consumer creating needs for its better unit operations knowledge. Computational fluid dynamics (CFD) have been widely used to better understand food thermal processes, one of the safest and most frequently used methods for food preservation. Fluid heating in enclosures is a complex phenomenon, which must be better understood. Although the relative convection importance at thermal liquid food process was recently evaluated trough CFD, viscosity influence as well as critical viscosity when a fluid behaves as a solid, has still not been evaluated. The present work has aimed to assess viscosity influence on thermal process lethality of in-package liquid food Typical thermal in-package process efficiency was compared by temperature profiles and mass average sterilization values (Fm) for model fluids with thermo-physical water properties and viscosities, varying from 0.1 to 106 times the water viscosity. It was evaluated, as well, a hypothetical solid with the same thermo-physical water properties. The sterilization process values have become lower when viscosity is increased until a critical value. From this found value, between 105 to 106 times higher than water viscosity, fluid behaves similar to a solid. Some typical foods whose rheological behavior is similar to those values were presented. Obtained results have confirmed that even fluid food can behave as solids during thermal process, once the heat transfer is carried out by conduction. The obtained results will contribute to thermal process design and evaluation and demonstrate the importance of rheological characterization and convection in fluid food thermal process.
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