Numerical Simulation Research On Ventilation Flow And Heat Transfer Law Of Grain Storage Based On Anisotropic Porosity

China is a developing country with a large population.Food security is the basis of rapid economic development and social stability and harmony.In 2020,China’s total grain output will reach 669.49 million tons,According to statistics,the loss of grain due to improper storage after grain harvest is about 5%.The main reason for the loss is that the improper control of temperature and humidity of grain pile in the storage process causes a large number of microorganisms and pests,and leads to the deterioration of grain quality.In order to effectively solve the problem of food safety storage,mechanical ventilation is usually used to cool and dehumidify the grain pile,so as to reduce the loss of grain in the process of storage and transportation.In the process of grain storage,due to the natural grading of grain grains containing impurities,large and small "impurity" accumulation areas will be formed in the grain pile,leading to the anisotropy of porosity in the grain pile,resulting in differences in ventilation resistance and ventilation uniformity in the process of ventilation,resulting in great differences in cooling rates in different ventilation directions,and even leading to the internal air pollution in the grain pile The temperature of the air is not uniform.Therefore,it is of great theoretical and practical significance to study the flow resistance and cooling effect in the process of grain storage ventilation on the basis of anisotropic porosity.This project focuses on the study of the flow and heat transfer law of the static grain pile(rice)under the condition of anisotropic porosity,and the research of the anisotropic porosity,flow and heat transfer law of the static grain pile(rice)based on the coupling method of EDEM and fluent.First of all,EDEM software was used to simulate the actual process of rice grain accumulation in the gravity free falling granary,and the static grain pile accumulation body was established.Combined with image-j software,the porosity in X,Y,Z(horizontal and vertical)directions of the static grain pile was obtained,and the anisotropic characteristics of the grain pile were analyzed.Then,on this basis,DEM-FLUENT coupling algorithm was used to carry out the simulation and prediction of flow and heat transfer law in grain pile under anisotropic porosity ventilation.The tortuosity of grain pile under ventilation was analyzed,and the process parameters such as ventilation resistance and energy consumption,cooling rate and ventilation uniformity under X,Y and Z ventilation directions were obtained At the same time,the ventilation resistance and energy consumption,cooling rate and ventilation uniformity were compared and analyzed under the condition of isotropic porosity.Finally,the temperature variation of grain pile under vertical ventilation was studied by experimental method,and the results were compared with the grain temperature data simulated by DEM-FLUENT coupling algorithm,which verified the DEM-FLUENT coupling model.The innovation of this study is that based on DEM-FLUENT coupling method,the anisotropy characteristics of stored grain pile and the law of air flow and heat transfer in the process of ventilation are simulated and analyzed,which provides a theoretical basis for the ventilation operation of stored grain.