Predicting the effective thermal conductivity of unfrozen, porous foods

In this study, it was shown that effective thermal conductivity models that are functions only of the components’ thermal conductivities and volume fractions could not be accurate for both granular-type porous foods (“external porosity”) and foam-type porous foods (“internal porosity”). An extra parameter is needed to make the model sufficiently flexible to allow it to be applied to porous foods with a range of different structures. A number of effective thermal conductivity models contain the required extra parameter, and of these, Krischer’s model appears to have received the greatest use in the food engineering literature; however, for isotropic materials it is recommended that a modified Maxwell model be used instead, because it assumes an isotropic physical structure, unlike Krischer’s model, and because the numerical value of the extra parameter may be estimated based on whether the food has internal or external porosity. A new procedure for predicting the effective thermal conductivity of non-frozen porous foods is presented as a flowchart.