Study On Formation And Development Of Rice Cracks Durying Storage With Ventilation

Nowadays the problem that broken rice is on the high side limites application of the technique of green grain storage severely. In this paper the mechnism of rice crack formation and propagation had been researched, which can be taken as theoretic foundation for the intelligent precision contol of rice cracks in storage systems. The details are as follows:1)Multiple molecular absorption theory, heat and mass transfer theory through porous media and stress theory were used to analyze the effect of temperature and humidity on rice hygroscopicity process and explain the reason for fissure formation. Results showed that during a long period of mositure adsorption, air relative humidity affected the whole hygroscopicity process, however, air temperature may only exhibited an obvious effect on hygroscopicity on the surface of rice. Meanwhile, both air temperature and relative humidity were positively correlated to the cracking rate of rice, due to moisture distributions at different distance of rough rice re-wetting.2)Change of mechanism of crack formation with time was studied, and the effect of chalkiness on fissuring of milled rice, under various environments of humid atmosphere thermodynamics, was also determined. The result showed that at the early stage of the process of crack formation, the mechanism of tensile stresss was in the leading position, while the mechanism of micro-cracks became dominate later; there was a transition phase between them, which the role of all factors would be weakened.3)The potential of resistance to rice cracks was studied by fractal theory. Four types of propagating models of stress cracks were established ; under moisture-adsorption condition, criterion for fissure propagation was given and surface energe of fractures was also deduced; the propagating kinetics of stress cracks was investigated. The results showed the propagating movement of rice moisture-adsorption crack was influenced by fractal effect and the potential of resistance to cracks depends on Mr of starch, which was not in glass state.4)The model of particulate packing was applied to figure out the relationship among rice fissuring, compression behavior and re-wetting of rice bulk. The particles were divided into thin layers horizontally to predict additional crack percentage for rough rice in a thin layer. The particulate packing was considered as pore network of unconsolidated porous media and its static charecteristic was analysis. Together with theory of mass and heat transfer of porous media, the particulate system may be simulated. Finally, it concerned moisture re-distribution in rough rice and air heating caused by fans.5)According to the quantitative analysis of rice cracked kernel, the paper classified researches on rice cracked kernel, discussed the damage stress and energy consumption of grain storage technology facilities, which related to rice cracked kernel occurance.