Analysis of the Heat Transfer Properties of a Dispersion System With Rice Grain Particles

ABSTRACT We investigated steady heat transfer in rice grains at various temperatures to evaluate the heat transfer properties of food solid–liquid dispersions and their particle size dependence. The two dispersion systems, comprising homogeneously dispersed and heterogeneously precipitated solutions with various volumetric solid–liquid fractions and diameters of rice grain particles, were prepared using media with different specific gravities. The thermal conductivity of both dispersion solutions depended on the solid–liquid fraction and particle diameter, and the effective interfacial area between the dispersion phase and the medium was suggested to contribute to thermal conductivity. That is, reducing the effective interfacial area was indicated to make heat transfer in the dispersion solution more efficient. In addition, the thermal conductivity of the dispersion phase was estimated using a model equation, and it was suggested that the thermal conductivity at the temperature above the gelatinization temperature might reflect the effect of water sorption by rice grains and gelatinization. The experimental and analytical methods used in this study could potentially provide useful information for simulations of thermal manipulation in the manufacturing and processing not only of rice grains but also other granular foods, especially food materials containing a large quantity of starch, such as beans.