Drying Rates of Thin Layer Rough Rice Drying Using Infrared Radiation

Rice drying with infrared radiation has been investigated during recent years and showed promising potential with improved quality and energy efficiency. However, due to limited penetration capability of infrared radiation, thin layer drying may be used in infrared dryer design. The objective of this study was to study the moisture removal characteristics of thin layer rough rice heated by infrared radiation and cooled with various methods, including natural cooling, forced air cooling and vacuum cooling. The rewetted rough rice samples with four different moisture contents, 16.7, 20.5, 23.6 and 25.7 % (wb), were dried with four different radiation intensities, 3616, 4023, 4685, and 5348 W/m, for four exposure times, 30, 60, 90, and120 s. The achieved grain temperatures ranged from 35.1oC to 68.4oC under the tested heating conditions. The vacuum and forced air cooling methods had more moisture removal than the natural cooling. The total moisture removal reached to 3.2, 3.5, and 3.8 percentage points for the rice heated to the temperature of 63.5 oC achieved with the infrared intensity of 5348 W/m and heating time of 120 s and followed by the natural cooling for 40 min, forced air cooling for 5 min and vacuum cooling for 10 min, respectively. It was concluded that infrared radiation thin layer drying of rough rice followed by cooling could be an effective approach to design infrared rice dryer for improving the drying rates and reducing energy consumption.