Drying of Rough Rice Using Heated Husk for Heat Transfer and Moisture Adsorption

Abstract

Abstract. Drying of small size samples usually represents a challenge to rice researchers. Using natural air drying to dry these samples exposes them to the fluctuations of ambient air conditions. Therefore, the goal of this research was to evaluate the suitability of drying small size rough rice samples using heated husk as a heat transfer and moisture adsorbent medium. The proposed drying technique could be an attainable process, particularly because it represents conduction heat and moisture transfer rather than natural air drying. The required amounts of rice husk were placed in aluminum containers and kept in an oven overnight to reach the desired temperature. Heated husk samples were mixed with rough rice and maintained for the desired drying duration; following which, the husk and rough rice mixtures were separated pneumatically. The separated rough rice samples were collected to determine moisture content, drying rate, and rice quality. The highest mixture temperature of 34.0°C was achieved at the highest husk to rough rice ratio of 1:2 and the highest husk temperature of 110°C after 4 minutes. A maximum of 6.4% moisture reduction points was achieved by mixing the rice husk to rough rice by 1:2 on a weight basis and employing heated rice husk at 100°C. The highest drying rate of 5.99%/h was achieved during the first hour of drying with the husk-to-rough rice ratio of 1:2 and the husk temperature of 100°C. Milled rice yield ranged between 63.4% and 72.0% while the head rice yield ranged between 39.9% and 67.9%. An empirical correlation was developed to calculate the normalized moisture content as a function of the husk to rough rice ratio, the husk temperature and drying duration with a coefficient of determination of 0.775 under the studied conditions. Keywords: Conduction drying, Heat transfer medium, Moisture absorbent, Rice husk, Rough rice.