| The problem of grain storage is a major issue related to our people's livelihood,in order to ensure the quality of the stored food,it is very important to ensure the safety of grain storage.There are many factors that affect the stability of grain storage ecosystem,the mechanical ventilation is one of important methods for change of grain storage environment.However,the research of ventilated grain pile only focus on cooling ventilation in China,and the importance of quality control and water ventilation is ignored.In view of the existing problems at the present stage,a cooling and water conservation ventilation system is built to control the temperature and moisture of grain simultaneously,so as to avoid the decline of grain quality and serious economic losses caused by water loss.As the main type of grain storage,the large warehouse has the characteristics of large span and storage volume.In order to promote the heat and moisture transfer between the area of grain storage and the air,the cross ventilation technology with long ventilation path is designed for grain storage.Based on the theory of heat and moisture balance and fluid flow in porous media,the mathematical model of heat and mass transfer in the process of grain storage ventilation is established.The process of constant temperature and humidity air entering the grain pile is simulated by the finite element difference method,and the heat and moisture exchange process of grain pile was studied.In order to explore the principles of temperature field and water distribution field of the ventilated grain pile,by the method of simulation prediction and experimental research,the influence of temperature and humidity of the air inlet on the cooling and water retention effect of the grain pile was analyzed.The specific research contents are as follows:1.Based on the geometric and physical model of the large-scale storehouse,the cross ventilation technology suitable for the large-span storehouse is constructed,and the perfecttheoretical basis for the cross ventilation of the large-scale storehouse is put forward.2.The static grain pile is regarded as a porous medium with hygroscopicity,and the convective heat transfer process between grain and intergranular fluidis studied.The cooling effect and water retention ventilation system of large warehouse is designed.Through the comparison of simulation prediction and experimental data,it is found that the trend of temperature and moisture of ventilated paddy has the same results,which can verify the correctness of mathematical model and the feasibility of numerical simulation method.3.The experimental study of cross ventilation with different process parameters was completed,and the cooling effect and water retention effects of the grain pile with different relative humidity of the air inlet were compared.It is found that when the relative humidity of the air inlet is too low,there is obvious water loss and the quality of grain is seriously damaged;when the relative humidity of the air inlet is too high,a large amount of water will gather in the grain layer near the air inlet,and mildew will occur in the local area;when the relative humidity difference between the air inlet and the initial grain pile is 0,the water drop of the grain pile at the end of ventilation is small and local moisture is recovered within the safe range.4.The mathematical and physical model of the cross ventilation of the large warehouse was established.The numerical analysis and prediction method was used to optimize the cooling and water retention ventilation process.The influence of the air temperature and the ventilation quantity of per ton grain on the temperature field and water distribution field of the grain storage was analyzed and compared,and the optimal process parameters of the cooling and water retention ventilation of the paddy in the large warehouse were obtained at the same time,it provides the basis for the operation of cross cooling and water retention ventilation. |
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