Fissure Occurrence in Vacuum Drying of Raw Rough Rice

为阐明高水分糙米真空干燥过程中干燥速度与裂纹发生的关系，进行了三年的研究。实验采用了合适的组合：真空压力、温度和相对湿度三个参数。此外，部分粗米被用来将糙米和粗米的结果联系起来。结果如下：1.在真空容器中，当绝对压力为5、40、75和101kPa(表压分别为-96、-61、-26和0 kpa)时，5kPa时的干燥速率显著高于较弱设定压力时的干燥速率。当真空容器在风箱中的温度为25、35和45℃时，尽管25和35℃的干燥速度较低，但在45℃时对干燥速度的影响显著增加。因此，加热和真空压力一起施加是必要的。由于排出潮湿的空气，真空容器内的相对湿度下降。干燥速率随环境湿度的降低和真空度的增加而略有增加。整个裂纹的发生，包括通常在糙米中引起的表面裂纹，随着干燥速度的增加而增加。然而，只发生了轻微的内部裂缝。使用糙米反而减少了表面裂纹的产生，但增加了内部裂纹的发生。糙米由于谷粒表面的薄皮破裂，容易被认为是随气压变化而受伤。然而，真空释放所需的时间与表面裂纹并没有密切的关系。品种间在干燥速率和裂缝发生方面的差异与常压热风干燥的差异程度相同。

To elucidate the relation between drying rate and fissure occurrence in vacuum drying of raw rough rice with high moisture, studies have been done for three years. The experiments were carried out using suitable combinatiouts : three parameters of vacuum pressure, temperature and relative humidity. Also the raw rough rice was partially used to relate the results of brown rice to rough rice. The results were as follows :1. With absolute pressures of 5, 40, 75 and 101 kPa (gauge pressure : -96, -61, -26 and 0 kPa) fixed in a vacuum container, drying rates at 5 kPa were remarkably higher than those at weaker set pressures.2. When the vacuum container was subjected to temperatures of 25, 35 and 45℃ in the air-oven, the effect on drying rate was a notable increase at 45℃ despite lower rates at 25 and 35℃. Thus it is necessary to apply heat together with vacuum pressure.3. Relative humidity inside the vacuum container dropped due to the evacuation of the humid air. Drying rate then increased a little with the lowering of the surrounding humidity and with increasing vacuum pressure.4. Whole fissture occurrence, which included surface cracks typically caused in brown rice, increased with the rise in drying rate. However, only a slight degree of internal fissuring occurred. The use of rough rice resulted in conversely less surface crack but higher internal fissure occurrence.5. Brown rice was easily considered to be injured with air pressure changes because of the rupture of the thin skin film on the grain surface. Nevertheless, the time required for relieving the vacuum was not closely related to surface cracking.6. Varietal differences in drying rate and fissure occurrence were recognized to be of the same degree as that of heated air drying under normal pressure.