Study On Heat And Moisture Coupling Law Of Bulk Wheat Stack During Ventilation

Food security affects national economic development and social stability.In the process of grain storage,the grain pile is affected by many factors,such as the change of external environment,the self-respiration of grain,microorganisms and so on,which leads to the local high temperature and humidity of grain pile,causing grain fever,mildew,diseases and pests,and damaging grain quality.The temperature and humidity of grain pile are important factors affecting the safety of grain storage.Mechanical ventilation is an important method to control the temperature and humidity of grain pile.In this paper,the distribution of temperature and humidity in the model warehouse of wheat grain pile under mechanical ventilation is studied by combining numerical simulation and experimental verification,and then the temperature and humidity variation of grain pile under different ventilation conditions in grain warehouse is studied,the main contents of this paper are as follows:(1)The main parameters describing porous medium and wet air in bulk wheat grain pile are determined,including porosity,permeability,thermal conductivity and specific heat capacity,Through grain slicing and image processing technology,the porosity of wheat grain pile under different vertical pressure is studied,and compared with the theoretical value of porosity,the relationship between pressure and porosity of grain pile is established,which is used for numerical simulation of mechanical ventilation process of bulk wheat grain pile.(2)According to the interaction of various fields in the grain pile,the heat and humidity coupling transfer law of wheat grain pile during ventilation is studied and the experimental research of wheat grain pile model warehouse under mechanical ventilation is carried out,which provided data support for the construction of heat and moisture coupling mathematical model under the ventilation state of grain pile.(3)According to the laws of conservation of momentum,mass and energy,and considering the natural respiration,hygroscopic and desorptive efficieney of grain pile,the coupled heat and humidity model of grain pile in the ventilation process is established.On this basis,the numerical simulation of mechanical ventilation of wheat grain pile model warehouse was carried out,and the results were compared with the experimental data.The results show that the change trend of temperature and humidity at each measuring point is basically consistent with the simulation value during the ventilation process,and the simulation results can better reflect the experimental law,and verify the accuracy of the numerical simulation method.(4)According to the mathematical model of grain pile ventilation,the numerical simulation of mechanical ventilation process of wheat grain pile in grain warehouse is carried out.In this paper,the temperature and humidity variation of wheat grain pile under different ventilation conditions was studied,the results show that the relative humidity transfer is relatively slow compared with the heat transfer speed in the process of storage ventilation;the distribution of temperature and humidity in grain pile has obvious stratified distribution.Keeping other ventilation conditions unchanged,with the increase of ventilation temperature of grain pile,the cooling rate slows down and the dehumidification rate speeds up;when only the ventilation relative humidity is changed,the cooling and dehumidification rate of grain pile slows down with the increase of ventilation relative humidity;when only the ventilation speed is considered,the cooling and dehumidification rate of grain pile speeds up with the increase of ventilation speed.