Yuthana Tirawanicahkul, Supawan Tirawanichakul and Elihya Saniso

pp. 347 - 363

Abstract

      The objectives of this research were to study basic physical parameters of three agricultural residues that could be used for prediction of paddy drying kinetics using desiccants, to investigate a suitable method for moisture reduction of fresh paddy using 3 absorbents, and to modify the drying model of Inoue et al. for determining the evolution of moisture transfer during the drying period. Rice husk, sago palm rachis and coconut husk were used as moisture desiccants in these experiments. From the results, it was concluded that the apparent density of all adsorbents was a linear function of moisture content whilst an equilibrium
moisture content equation following Hendersonís model gave the best fit to the experimental results. From studying the relationship between moisture ratio and drying time under the condition of drying temperatures of 30, 50 and 70°C, air flow rate of 1.6 m/s and initial moisture content of absorbents of 15, 20 and
27% dry-basis, it was shown that the moisture ratio decreased when drying time increased. In addition, the thin-layer desiccant drying equation following of the Page model can appropriately explain the evolution of moisture content of paddy over the drying time. The diffusion coefficient of all absorbents, which was in the range of 1x10^-8 to 6x10^-8 m²/h, was relatively dependent on drying temperature and inversely related to drying time. The diffusivity of coconut husk had the highest value compared to the other absorbents.
       The simulating modified mathematical model to determine drying kinetics of paddy using absorption technique and the simulated results had good relation to the experimental results for all adsorbents.

Keywords

• agricultural residues
• drying
• equilibrium moisture content
• diffusion coefficient
• Mathematical model