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率与裂缝发生的关系，进行了为期三年的研究。采用合适的真空压力、温度和相对湿度三个参数组合进行实验。此外，还将糙米与糙米的测定结果进行了部分对比。实验结果如下：1.实验结果表明：当真空容器内的绝对压力分别为5、40、75和101 kPa（表压分别为-96、-61、-26和0 kPa）时，5 kPa下的干燥速率明显高于较弱设定压力下的干燥速率。当真空容器在空气烘箱中经受25、35和45℃的温度时，尽管25和35℃的干燥速率较低，但45℃对干燥速率的影响显著增加。因此，在施加真空压力的同时加热是必要的。真空容器内相对湿度下降，因为抽走了潮湿的空气。随着周围湿度的降低和真空压力的增大，干燥速率略有增加。随着干燥速率的增加，糙米的整体裂缝发生率增加，其中包括糙米表面裂缝。然而，只发生了轻微的内裂。相反，粗米的使用减少了表面裂缝的发生，但增加了内部裂缝的发生。糙米容易受到气压变化的伤害，因为糙米表面的薄膜会破裂。然而，消除真空所需的时间与表面裂纹没有密切的关系。干燥速率和裂缝发生的品种差异被认为与常压下加热空气干燥的程度相同。

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.