Simulation Study On The Heat And Moisture Transfer Law Of Cooling And Ventilation Of Grain Storage In Shallow Circular Silos And The Growth Rate Of Pest

Food crops are one of basic means of subsistence for people’s survival and development,and they are strategic means of production related to the national economy and people’s livelihood.In the process of grain storage,it is often attacked by pests,molds and other harmful organisms,resulting in loss of weight and quality.The survival activities of biological components such as pests and molds in the grain piles are related to the temperature and moisture of the grain piles.In order to control the reproduction and growth of insects and molds in the grain piles and ensure the original quality and quantity of grains to the greatest extent,mechanical ventilation is usually adopted to rapidly reduce the temperature of the grain piles to a reasonable range.In the process of mechanical ventilation,cooling will also cause the loss of moisture content in the grain pile,which will cause economic losses to grain storage enterprises,so the importance of cooling and water retention cannot be ignored.As a new type of granary,the shallow round silo has the advantages of better grain storage stability and more convenient way of entering and leaving the silo,which makes the shallow round silo develop in an irreversible trend.Therefore,it is of great practical significance to study the variation law of the internal temperature and water content of the grain pile under different ventilation conditions and the influence on the growth rate of pests,and to explore the optimal ventilation process.In this dissertation,the theory of porous media flow and heat-moisture coupling is firstly adopted,and the coordinate transformation is used to obtain the momentum,mass and energy conservation equations in the shallow circular silo grain heap under the cylindrical coordinate system,and the prediction of the ventilation process of the shallow circular silo grain is constructed.Mathematical model for changes in parameters such as temperature,moisture,and pest succession.Secondly,using Fortran language programming and finite difference method to solve the constructed mathematical model,and then simulate the air flow velocity,temperature field,moisture field and pest growth rate inside the grain pile during the ventilation process.The main contents of this dissertation are as follows:1.the theoretical basis of ventilation for grain storage is systematically introduced,and the characteristics of shallow-circle grain storage are analyzed and studied.Based on the theory of porous media flow and heat-moisture coupled heat transfer,combined with the geometric and physical model of the shallow circular warehouse,a ventilation mathematical model of the shallow circular warehouse with cone bottom and flat bottom is constructed.2.The numerical calculation method based on Fortran language has been improved,and the grid is divided into shallow circular bins with typical domestic structural dimensions,and the grid spacing and the difference operator of internal nodes and boundary nodes are defined.Based on the finite difference method,the partial differential equations of the multi-field coupling models such as the internal velocity,temperature,moisture and insect population density of the grain pile during the ventilation process were solved,and the computer program and post-processing program for cooling the shallow circular silo and keeping water and ventilating were written.3.Numerical simulation research was carried out on the condition of unventilated air,and the effect of ventilation on the cooling and water retention of grain piles and the influence on the growth rate of pests under the conditions of different warehouse types,various types of ventilation channels,and three types of ton of grain ventilation were analyzed.By analyzing the distribution of airflow velocity field,cooling rate,water retention effect,inhibition of pest growth and ventilation energy consumption,the optimal process parameters for cooling water,water retention and ventilation in shallow round warehouse are obtained,which provides a theoretical basis for shallow round warehouse cooling,water retention and ventilation.At the same time,the research results are also beneficial to improve the design of granary ventilation process equipment.4.Finally,use the commercial CFD(Computational Fluid Dynamics)software to numerically simulate the ventilation situation of the shallow circular warehouse,and analyze and compare the agreement between the prediction results of the CFD software and the selfprogrammed results.At the same time,through the self-built small experimental warehouse,the experimental data collection and analysis are completed.The CFD numerical simulation results and measured data are compared with the simulation results of the self-compiled computer program respectively to verify and verify the correctness of the self-compiled program simulation.The conclusions of this study are beneficial to formulate a reasonable ventilation plan,reduce the loss in the process of grain storage,save the cost of grain storage,and improve economic benefits,and have guiding significance.