MODELING THE THERMAL-CONDUCTIVITY OF STARCH-WATER GELS

The thermal conductivity of starch gels, ranging in water content from 51 to 97% by mass, was measured using the thermal probe method and th e thermal conductivity of starch itself was determined using a revised analysis of the null point method of Sakiyama et al. (1993), taking i nto account the effect of hydration. The thermal conductivity of hydra ted starch (mass fraction of water = 0.22) was found to be 0.364, 0.38 6 and 0.388 W m(-1) K-1 at 10, 50 and 80 degrees C, respectively, and its density at 20 degrees C was estimated to be 1.38x10-(3)kgm(-3). Th e corresponding effective thermal conductivities and density of dry st arch were estimated as: 0.293, 0.305 and 0.301 Wm(-1) K-1 and 1.54kgm( -3), respectively. The measured thermal conductivities of starch gels followed quite closely intermediate models such as the Maxwell model o r the parallel-series model, but were inconsistent with either the par allel or series models alone. (C) 1997 Elsevier Science Limited.