Studies on Sun Drying of Raw Rough Rice (Part 3)

Drying Characteristics and Heat Balance in Plane Surface Bed

Abstract

Solar radiant energy incident on the plane surface of 10, 7.5 and 5cm thick beds of rough rice intermittently stirred once every hour resulted in drying rates of 0.18, 0.28 and 0.35 percent per hour, respectively. As the bed was made thicker, total hours required for drying down to storage moisture content increased, while there was little difference in hourly drying capacity. When 5cm thick beds were intermittently stirred once every 2, 1 and 0.5 hour, a corresponding increase in drying rate was noted, but the rise in surface temperature and the level of grain crack remained low. Consumptive distribution of solar radiant energy on a fine day was almost constant and no more than 10 to 15% of the total incident radiation was used for evaporation of the moisture in rough rice. On such fine days, lowest values of reflectance (albedo) occurred about noon when the solar elevation angle approached maximum. The daily mean albedo was 0.38.