Numerical Simulation Of Heat And Moisture Transfer In Stored Grains During The Cooling And Drying Ventilation

China is the most populous country in the world while it is also a large agricultural country. The food quantity, quality and safety are directly related to the development of the national economics and social stability. Statistics show that grain output in China is up to more than 500 million tons annually, but only 80% of the grains can be used as food material. 20% of the grains were lost in the storage process due to the improper storage. The previous study finds that the major factors resulting in the loss of grains in the storage are temperature and moisture content. Therefore, keeping the grain temperature and moisture content at appropriately level during the cooling and drying ventilation can achieve the grain security storage.Based on the theory of heat and mass transfer in porous media, this paper mainly studied the heat and moisture transfer in stored grains during the cooling and drying ventilation by CFD simulation method and experimental method. It was on the basis of mechanical ventilation for grain storage and the theoretical basis of CFD-based numerical simulation. The establishment of physical models and mathematical models of heat and moisture transfer in stored grains during the cooling and drying ventilation were based on a silo and a large warehouse.First of all, this paper analyzed the previous work about mechanical ventilation in grains storage and the research progress in this field at home and abroad. Then this paper introduced the theory of mechanical ventilation in grains storage, heat and mass transfer in porous media and CFD numerical simulation.Secondly, this paper proposed a mathematical model of heat and moisture transfer coupled in stored grains during the cooling and drying ventilation based on the theory of heat and mass transfer in porous media.Finally, two-dimensional physical model and three-dimensional physical models were established with a silo and a large warehouse. This paper researched the changes of grains temperature and moisture content during the cooling and drying ventilation by CFD numerical simulation method and obtained the basic laws of heat transfer and moisture migration in stored grains during the cooling and drying ventilation. The results show that: the simulation results agrees with the data of the temperature and moisture content in stored grains during the actual mechanical ventilation with the theoretical analysis and experimental results verify and the results verify the mathematical model proposed in this paper was accurate. Cooling and drying ventilation have a good effect on cooling and precipitation. Cooling and precipitation exist simultaneously in the cooling and drying ventilation process and the speed of cooling front was much faster than the drying front. It was often manifested in the ventilation process that the cooling has been completed while the drying process was still ongoing. Numerical simulation technology was introduced to this traditional area with the development of computational fluid dynamics. It provided a reliable and comprehensive visual research tools for the mechanical ventilation design and the ventilation system in future.