Direct and indirect determination of the effective thermal diffusivity of granular starch

Abstract

The effective thermal diffusivity ( α eff) of two granular starches was determined directly and indirectly, using the heated probe method of unsteady-state heat conduction. In the direct method, α eff was determined from transient time-temperature data, obtained with a thermocouple placed near the heated line source. In the indirect method, α eff was calculated from the effective thermal conductivity ( λ eff ), the bulk density ( ϱ b ), and the specific heat (C p ) of the granular starch in the moisture range 0–30% (dry basis) and at ϱ b = 700 kg/m 3, T = 25°C. The specific heat of the starches, determined by differential scanning calorimetry, increased linearly from 1260 to 1800 kJ/kg K in the moisture range 0–30% (dry basis). The indirect method yielded more accurate values of α eff (near 1 × 10 −7m 2/s) than the direct measurement, as concluded from the F-test at level of significance 5%.