Experimental and numerical study of intermittent drying of rough rice in a combined FIR-dryer

Abstract

Moisture variation and fissure formation of rice kernels during multi-stage intermittent drying (MSID) were simulated and analyzed based on the experimental data obtained in a laboratory-scale infrared-assisted vibratory bed dryer. The variations of drying parameters included far-infrared radiation (FIR) intensity (0, 1000 and 2000 W m−2), inlet drying air temperature (30, 40 and 50 °C), drying duration (15, 30 and 40 min), and tempering ratio (0, 2, 4 and 6). Two-dimensional moisture distribution within individual kernel was predicted. Drying rate, percentage of the cracked kernel (PCK), and specific energy consumption (SEC) were also determined, experimentally. By assessing PCK and SEC and simulation results, it was found that the magnitude of 10% d.b. mm−1 was considered as an index for the critical value for moisture content gradient (MCG) to achieve the suitable drying and tempering duration. It was further recommended that the intermittent drying duration at each stage should be selected in such a way that the MCG value does not exceed the critical level and the shortest possible tempering duration should be chosen in a manner that at least 40% of critical level of MCG be eliminated. The suitable treatment for intermittent drying was selected at FIR intensity of 1000 W m−2, inlet air temperature in 40 °C, drying duration in 30 min, and tempering ratio in 4.