Effects of Air Temperature and Humidity on Hygroscopic Cracking in Rice
The generation of rice moisture cracks is largely due to the temperature and humidity in the air. Specifically, how much impact it has, we need to obtain some experimental data. So this article mainly uses some mature technology, scientific instruments such as self-reporting temperature and humidity meter and corresponding data to analyze the influence of air temperature and humidity on moisture absorption crack of rice.
Grain dynamics believes that the cause of cracks in the grain is that the stress somewhere inside exceeds the tensile strength limit at that location. For rice grain, its ultimate tensile strength is affected by many factors such as variety, maturity, ambient temperature, humidity, and its own moisture content. Among them, the effects of soil moisture, ambient temperature and environmental humidity are more obvious. Nowadays, we often try to use temperature and humidity self-recording devices to measure the changes in temperature and humidity in the environment. When we understand the environment, we can respond in time and make adjustments. The soil moisture is also measured by a soil moisture analyzer. Even in the cross section of the same grain, the grain tensile strength of the grain layers is different due to the significant difference in the composition of the grains from the inside to the outside. At a certain moisture content and temperature, rice grains will undergo glass transition, the material properties will become brittle, and the ability to tolerate deformation will become smaller. Even if the deformation is small, the stress that exceeds the ultimate tensile strength of rice will be generated. When the initial water content of rice is between 10% and 25%, the glass transition temperature fluctuates within the range of 30 to 45°C. In actual production, the initial moisture content of rice during the conditioning of rice is generally about 11% to 12%, and the quenching and tempering temperature is usually room temperature, ie, 25 to 35° C., and the temperature is controlled by a self-reporting temperature and humidity meter. Less than the glass transition temperature of rice, the glass transition does not occur during the humidification process. According to the theory of stress, with the absorption of moisture, the volume inside and outside the grain will undergo different degrees of expansion and contraction, resulting in a change in the internal stress balance relationship. The surface of the grain is under pressure and the heart is in tension.
The results showed that under certain relative humidity, if the temperature decreases or the relative humidity decreases, the pressure difference between the water vapor partial pressure on the capillary meniscus and the water vapor partial pressure on the capillary wall decreases, and the capillary condensation in the grain decreases. The phenomenon will be correspondingly weakened, the tendency of water vapor in the grain to form liquid water will slow down, and the imbalance of stress caused by differences in the degree of expansion inside and outside the grain will be relieved, thus slowing down the process of moisture cracking in rice to some extent. At a certain relative humidity, when the temperature is increased, or when the relative humidity is increased at a certain temperature, the pressure difference between the water vapor partial pressure on the capillary meniscus and the water vapor partial pressure on the capillary wall increases, and the capillary condensation of rice grains will be correspondingly increased. Intensified, and to a certain extent, accelerated the development of moisture-absorbing cracks in rice.
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