Glass Transition Behavior of Rice Grain in Hot Air Drying Based on Acoustic Emission Method
The glass transition behavior during hot air drying of rice will lead to changes in the internal micro-structure and physical properties of the grains,which will lead to drying stress and internal cracks and even crack.In this paper,the rice drying mathematical model was used to simulate the glass transition process of grains.An experi-mental platform for real-time acoustic emission detection of cracks in rice grains was established to monitor the rup-ture sound waves during grain drying.The results indicated that the glass transition time of rice grain was advanced with the decrease of drying temperature during hot air drying.When the isothermal drying temperature was between 35 ℃ and 45℃,the grains changed rapidly from glassy state to rubbery state in the heating stage and gradually from rubbery state to glassy state in the drying stage.And the lower the drying temperature,the faster the grain glass tran-sition rate.When the drying temperature was greater than 44℃,the grains would remain rubbery until the end of drying.When the isothermal drying temperature was 37-41 ℃,the acoustic emission signal of the grain was rela-tively rich.The glass transition behavior of grains in the main drying stage would promote the generation of cracks.At about 39 ℃,the acoustic signal generated by the grain rupture was the strongest.At the drying temperature of 37-41 ℃,the glass transition behavior of rice grains had a time sequence and the time period of the fracture acoustic e-mission signal concentration area coincided with the glass transition time period.
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