The influence of porosity on the thermal diffusivity of foods

Abstract

Thermal diffusivity is an important parameter in unsteady-state heat transfer processes. Compared to other physical properties, there appears to be very few predictive models for thermal diffusivity in the literature. Most experimental studies have focussed on the influence of moisture content and temperature on thermal diffusivity and there is very little about the influence of porosity. In this study, the effects of porosity on thermal diffusivity are examined for selected foods and thermal diffusivity models from the literature are compared against measured data. The thermal diffusivity model proposed by Choi and Okos based on a weighted arithmetic mean of the components’ thermal diffusivities is not suitable for porous foods, resulting in large prediction errors. Applying a similar approach based on the harmonic mean rather than the arithmetic mean provided closer estimates of thermal diffusivity for both types of porous foods considered, but still produced unacceptable prediction errors (e.g. greater than 100 % when applied to model the thermal diffusivity of rice). Thermal diffusivity predicted from effective thermal conductivity, effective density and effective specific heat capacity data also resulted in unacceptable error. It is clear that there is scope for more work to be done in this area.