Numerical Simulation Study On Yellowing Of Stored Rice Under Typical Local Climatic Conditions

China is the largest developing country in the world,and it is also the country with the largest population in the world.The food issue is not only an economic issue,but also closely linked to national security and social stability.It is the foundation and guarantee for the people to live and work in peace and contentment.During the grain storage,the quality of grain depends on the temperature and moisture of the bulk grain.If the temperature and moisture content of grain are inappropriately controlled in the stored grain,it will result in local hot spot,mildew and yellowing in the bulk grain,and give rise to the deterioration of the bulk grain.Therefore,it is of great significance to ensure the quality of stored grain and realize the safe storage of grain.This subject takes the concrete squat silo as the research object of rice storage.The squat silo can be used as long-term grain storage.Generally speaking,it takes three years as a storage cycle,and the annual storage environment and process are basically the same.The storage cycle of this research is one year,starting from the warehousing of rice.The storage process is natural seal storage ? mechanical ventilation(or aeration)and cooling ? natural seal storage ? mechanical ventilation(or aeration)and cooling ? natural seal storage successively.The ventilation duration and ventilation times in different grain storage ecological areas are slightly different.In accordance with the actual operation of local grain storage,the mechanical ventilation is separately divided into grain cooling ventilation based on artificial cold source and aeration based on local cold air.In this research,Sanya,Nanchang and Changchun grain depots in three different grain storage ecological regions in the south,middle and north of China were selected as representatives.This study adopted the method of combining numerical simulation and field monitoring investigation to deeply explore the mechanisms of heat and moisture transfer and yellowing of stored rice under local climate conditions,as well as the variation mechanism of the bulk grain temperature and moisture.Firstly,based on the theory of heat and mass transfer in porous media and the principle of local heat balance,a mathematical model of internal flow and coupled heat and moisture transfer in the bulk grain were implemented.Combined with the mathematical model of rice yellowing,the variation laws of temperature,moisture and yellowing during one year of rice storage under typical local climate conditions were simulated by numerical simulation.Secondly,the relevant mathematical models were verified and validation by the monitoring data using the field test method of the actual granary(real granary).The research contents are as follows:1)The mechanism and analysis of airflow,heat,mass transfer and respiration in hygroscopic porous media.2)The implement of mathematical model.The mathematical model includes the mathematical model of heat and moisture coupling transfer in the bulk grain during seal storage and ventilation;The mathematical model of rice yellowing obtained by regression based on relative experimental research data.3)The verification and validation of mathematical model.By the comparative analysis of measured date and numerical simulation results,the conclusion was that the experimental investigation results and numerical simulation results corresponded with each other relatively,and the maximum error was within the acceptable range,which verified the rationality of the relevant mathematical models.4)The numerical simulation and analysis of rice yellowing in typical squat silo under local climate conditions(Taking Sanya,Nanchang and Changchun as examples).Specifically including: Under local climate conditions(Environmental temperature and moisture content outside the silos,solar radiation),the variation laws of temperature,moisture and yellowing when stored rice completely in a seal environment.Under local climate conditions,comparative research on the spatial and temporal distribution of temperature,moisture and yellowing of rice stored in complete seal storage and timely ventilated storage.It's compared and analyzed the changes of temperature,moisture and yellowing of rice stored with or without ventilation through the year.The results indicated that ventilation(or aeration)and cooling effect is significant,the temperature of the bulk grain is significantly lowed,and the moisture of the bulk grain is relatively reduced,which thereby effectively inhibit the yellowing rate of stored rice.5)Under local climate conditions,the numerical simulation and analysis of rice yellowing under different squat silo structures.The distribution of temperature,moisture and yellowness of rice bulk grain was simulated when the ratios of height to diameter were 2.0,1.0and 0.5 for grain storage respectively.The research results showed that when rice was stored for one year,there's little difference in the average moisture of rice under the three silo structures,and the average temperature and yellowness of rice in squat silo with the ratio of height to diameter of 1.0 for grain storage were the lowest.The results showed that the squat silo with the ratio of height to diameter of 1.0 was more suitable for grain storage.The research results are helpful to solve the problem of rice storage quality prediction,so as to provide reference and theoretical basis for practical safe grain storage.