Study On Heat And Moisture Transfer And Pipe Network Optimization Of Different Aeration Modes In Squat Silo

Grain storage mechanical aeration technology is the main technology to regulate the temperature and humidity of grain pile and maintain the quality of stored grain,but there are problems such as difficulty in cooling,excessive water loss and high energy consumption in the aeration process of squat silo.Understanding the heat and moisture transfer law in the grain storage aeration process is the premise of optimizing the grain storage mechanical aeration system and process.Therefore,this dissertation established a mathematical model of grain aeration cooling,used numerical simulation method to study the heat and moisture transfer law in the aeration process of squat silo.A comparative study of three commonly used geosyncline aeration system was conducted.A new radial aeration system was designed to address the shortcomings of the geosyncline aeration system and was compared with the geosyncline aeration system to evaluate its feasibility and application value.The specific research contents and conclusions are as follows:(1)The establishment of mathematical model for grain aeration cooling.The aeration and cooling process of grain storage was studied by combining theory with experiment.According to the characteristics of wheat grain pile containing wet unsaturated porous media,the key parameters of grain pile and wet air were determined.The characteristics of heat and mass transfer in the process of grain aeration cooling were analyzed,and the heat and moisture transfer model of grain aeration cooling was established by using the local heat non-equilibrium method.The accuracy of the model was verified by the aeration cooling experiment on the selfbuilt small experimental silo.(2)Numerical simulation of heat and moisture transfer in geosyncline aeration system.According to different types of geosyncline(radial,comb and Gui),the model of geosyncline aeration system was established,and the aeration and cooling characteristics of each geosyncline aeration system under positive pressure upward aeration and negative pressure downward aeration were compared and analyzed.The results showed that the cooling effect,water uniformity and water retention of the negative pressure downward aeration were better than that of the positive pressure upward aeration.Among the three types of geosyncline,the Gui-shaped geosyncline had the best comprehensive performance of aeration cooling.(3)Heat and moisture transfer law and pipe network optimization of radial aeration system.The heat and moisture transfer law of the radial aeration system was studied by numerical simulation,and the height of the branch air duct in the aeration pipe network was optimized.The results showed that the airflow distribution of the radial aeration system was complex and there were local aeration dead angles.After aeration,most areas of the grain pile cooled well,but there were local high temperatures.Negative pressure downward aeration had better cooling effect,temperature uniformity and water retention,but there was water stratification.After optimizing the pipe network for the squat silo with a diameter of 25 m and a grain loading height of 20 m,the optimal height of the branch air duct was 8.5 m.The cooling effect and temperature uniformity of the grain pile had little change,but the air flow uniformity,water retention,water uniformity and energy saving effect had been effectively improved.(4)Comparative study of geosyncline aeration and radial aeration.The cooling effects of the Gui-shaped geosyncline aeration system and the radial aeration system with the branch duct height of 8.5 m under different air volume were compared and studied.The results showed that the cooling effect and aeration uniformity of the radial aeration system were worse than that of the geosyncline aeration system at low air volume,but at high air volume,its aeration uniformity was effectively improved,the cooling effect and water retention performance had obvious advantages,and the system had outstanding advantages of low aeration resistance and low energy consumption.