Experimental benchmarking of diffusion and reduced models for convective drying of single rice grains

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Abstract
In this work, the drying behavior of single rice grains at moderate and elevated air temperatures (i.e. 60 °C, 120 °C, and 140 °C) is experimentally investigated by using a magnetic suspension balance system. To describe the experimental drying behavior, a diffusion model is developed. The reference moisture diffusivity of the rice grains is determined by using an inverse method, whereas other thermo-physical properties are measured. Next, the diffusion model is reduced to a semi-empirical model within the frame of reaction engineering approach (REA). Both models are successfully benchmarked against the experimental observations. The results indicate that the moisture diffusivity of rice grains can be represented as a linear function of the moisture content and the drying process at high temperatures is controlled by both intra- and extra-particle mass transfer resistances. In addition to these results, this study favors a practical application of the REA in drying calculations to derive a simple, robust, and extrapolative semi-empirical model since the parameter of this model seems to be insensitive to variations of drying conditions.

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