Impact of grain layer thickness on rough rice drying kinetics parameters

The literature revealed a gap in rough rice's drying kinetic parameters data under layer drying and isothermal conditions. Therefore the goal of the present study was to explore the drying kinetics parameters of rough rice under isothermal conditions and layer thicknesses. Rough rice was dried under the drying temperature range of 40–100 °C and grain layer thickness of 2.5–10.0 cm for 6 h. Rough rice moisture content and moisture ratio decreased with the increase of drying temperature, the drying duration, and the shallow grain layer thickness. The maximum drying rate of 4.63%/h was achieved at the drying temperature of 100 °C, the grain height of 2.5 cm, and during the first hour of the drying process. Among the four tested models (Page, Newton, Logarithmic, and Henderson & Pabis), the Page model showed the best fit under thirty-five cases, with R2 ranging between 0.9979 and 0.9021. The highest effective moisture diffusivity of 5.929 × 10−9 m2/s was obtained at the drying temperature of 100 °C and the grain layer thickness of 2.5 cm. The activation energy was 25.40 kJ/mol and 29.46 kJ/mol, corresponding to the grain layer thickness of 2.5 and 10.0 cm, respectively. Accordingly, the present study proved that layer drying would expedite the drying process.