Drying Characteristics of a Single Grain of Rough Rice

Abstract

The authors constructed an apparatus for measuring drying characteristics of a single grain of rough rice, which was showed in Fig. 1.
The performance of the apparatus was as follows:
1. The temperature, the relative humidity and the velocity of air were controlled within a range of (20-60)±0.5°C (0∼90)±1% R. H., 1.5±0.05m/s, 0.05±0.005m/s, respectively.
2. The glass beam to measure the grain weight had the senesibility of 2μg and an accuracy of 1/20, 000. The air current could be maintained around the rice while reading the weight of it was measured. The experimental results under the conditions shown in Table 1 were as follows.
1. The drying curves of unhulled rice obtained were shown in Figs. 4-1, 4-2, 4-3.
2. The drying curve of one grain of unhulled rice showed three stages distinctly, viz, the initial rapid drying period, the constant rate period and the falling rate period, except for the drying curves with 80% relative humidity for any air temperatures.
3. The initial short rapid drying period seemed a constant rate period, but its true nature could not be determined.
4. The constant rate period was in the range of 15.5-5.7% db/h and was influenced by both the temperature and the relative humidity of air.
5. The heigher the temperature and the lower the relative humidity of the air, the greater was the falling rate. when the air temperature was the same, the slope of falling rate curves was the same regardless of the humidify of air. Fig. 5-1. When the relative humidity was kept constant, the slope of falling rate curves depended upon the temperature of the air stream, Fig. 5-2. Therefore the slope of falling rate curves was little influenced by the rleative humidity. This tendency was also shown in Figs. 6-1 and 6-2 whose abscisae were time and the ordinate the moisture content ratio.
6. At a constant relative humidity, the equi librium moisture contents became almost the same in spite of difference in air temperatures.