Measuring the Moisture Diffusion Coefficient of Some Grains of an Anomalous Shapes

Abstract

As a consequence of the similar form of the heat-flow and the mass-flow equations, the solutions for both equations must also be similar. Therefore, from the solution of the heat-flow equation, the solution of the mass-transfer equation is obtained when the mass fraction is substituted for the temperature T and the diffusion coefficient D for the thermal diffusivity α.
For this reason, using the Smith's geometry index for the transient heat transfer from anomalous shapes, the mass (moisture) diffusion coefficients of the grains of an anomalous shapes were measured from drying curves. The results were summarized as follows.
1) The equation of the drying curve was determined by Deming's method of the least square. It is believed that the Henderson's method of three points approximation is accurate enough to estimate the equilibrium moisture content.
2) The decreasing order of diffusion coefficient is as follows: wheat>unhulled rice>polished rice>hulled rice.
3) The Arrhenius' equation was generally applicable for relating the diffusion coefficient to temperature and the following results were obtained.
D=5.19×10^-3e^-3.29×103/T
(unhulled rice)
D=7.09×10^-4e^-2.85×103/T
(hulled rice)
D=7.34×10^-3e^-3.58×103/T
(polished rice)
D=5.77×10^-3e^-3.00×103/T
(wheat)