Numerical Simulation Of Glass Transition Process In Rice Kernel Drying

Aiming at the problem of fissuring in the drying process of rice,this paper reconstructed the three-dimensional aptamer model of rice by image method,and used COMSOL Muiltiphysics multi-physics coupling software to simulate the heat and mass transfer of rice during drying process.Further research on the drying process of rice based on the theory of glass transition and the following results are as follows:1)Study the rice drying-tempering process.Simulated isothermal drying-tempering and temperature-drying-tempering found that tempering can redistribute moisture and the moisture gradient is greatly reduced.The larger drying/tempering ratio is,the larger the moisture gradient decreases in the tempering stage;Isothermal drying-tempering same drying/tempering ratio can effectively reduce the fissuring rate of rice at 20min.In order to better reduce the moisture gradient,an optimization isothermal drying-tempering process was proposed.When the temperature was 60?,the drying/tempering ratio of 1:1 tempering time was 10 min in the first 40 min,and then the tempering time was 20min to effectively reduce the moisture gradient inside the rice.The variable temperature drying-tempering process can effectively reduce the rice fissuring rate when the tempering temperature is higher than the drying temperature of 10?15?.2)The cooling methods of extreme cooling,square wave cooling,linear cooling and cosine cooling were studied.The glass transition of rice cooling process after drying was completed.It was found that the glass transition is no significant difference of the rice after drying at different temperatures were vitrified at extreme cooling and cosine cooling.Square wave cooling has a significant effect on the glass transition of rice,and it was found that the glass transition process occurs at a temperature range.Square wave cooling and linear cooling process cooling have significant effects on glass transition at different cooling times.Linear cooling for 40 min completes the glass transition time of up to 612 s,the shortest 153 s;there is no significant difference in cooling for 20 min.At the same time,it was found that the rice has different the glass transition modes under different cooling modes,and the square wave cooling is particularly prominent.3)The study simulates the completion of drying at 60?,and after cooling for the same time in the same cooling mode,it was found that there is almost no difference in the completion of the glass transition time.It can be seen that the tempering time has little effect on the glass transition phenomenon under the same cooling mode.;After the drying at 60? was completed,the glass transition time was 348s and 144s in the square wave cooling and the extreme cooling mode,respectively.After the tempering same time,the different cooling methods had significant effects on the glass transition phenomenon.