Experimental Study On The Development And Control Of Stress Cracks Of Rough Rice In Drying

1)The stress cracks of rice kernel during drying were originated along lateral axis of rice kernel. The sequence of its formation was one crack first, then twocracks, and checked cracks at last. New cracks were formed after drying. Thecracks were decreased under low air temperature and high air flow rate, low initial moisture content and high final moisture content, slow cooling and lowtemperature storage.2)The morphosis of endosperm tissue and the micro-structure of stress cracks of rice kernel after drying were studied by Scanning Electronic Microscope. The structure of endosperm tissue was damaged slightly in sun drying. The structure of endosperm tissue was damaged seriously during drying with heated air. There was a lot of stress cracks in the endosperm tissue of rice kernel.3)The generation of stress cracks was due to the change of chemicalcomponent and the complexity of structure of rough rice kernel in drying. The temperature gradient and moisture gradient were the important factors for the formation of stress cracks. The stress cracks of rice kernel belong to brittlerupture.4)The mechanical properties of rough rice kernel were studied. The ultimate strength of rice kernel was greater with low moisture content and low dryingtemperature. The mathematical equation was developed on the strength of ricekernel which was a function of drying temperature, and moisture content of rice kernel.5)The glass transition theory was applied on the drying of rough rice kernel. A glass transition will occur in the temperature range typically encountered during rough rice drying. The mathematical equation was developed on the glass transition temperature and the moisture content of rough rice kernel. The glass transition theory was used to explain the mechanism of crack formation.6)The initiation and propagation of stress cracks of rice kernel were studied by the fractal theory. The stress cracks of rice kernel were observed by Scanning Electronic Microscope. The stress cracks of rice kernel possessed a fractal character. Four types of propagating models of stress cracks were established. The propagating kinetics of stress cracks was studied.7)A flat-bed counter flow rice drier was developed successfully. Test results showed that the drying capacity was large~ the energy consumption was small, and the quality of rice was good. The higher drying rate of this drier was due to low air temperature and high air flow rate.