Research On Coupled Heat And Moisture Transfer In The Warehouse During Natural Storage And Mechanical Ventilation Process

In the process of the grain natural storage,milde00 wing occurs when thetemperature and moisture increase in the local area of grain bulks due to the influence of the external environment and internal grain respiration,which decreases the food quality and endangers the safety of grain storage,thus the temperature and moisture of grain bulk are two important parameters which should be paid attention to during the natural storage.With the purpose of having a safe food storage,the warehousing mechanical ventilation is the main technical means to reduce internal temperature and moisture of the grain.By combining the numerical simulation with experiment method and taking the grain bulk stored in the warehouse as the research object,the research focuses on the heat and moisture transfer of the grain in warehouse storage(grain bulk)during the process of natural storage and mechanical ventilation under local climate conditions,exploring the law of internal temperature and moisture change effected by multi-field coupling with moisture absorption and desorption as well as the respiration,providing a theoretical basis for preventing local mildew and applying mechanical ventilation in grain warehouse.From the perspective of biological porous medium grain fluid with the natural convection,the research initially uses the macro volume method and local thermal equilibrium principle to analyze the internal flow field,temperature field,moisture field of coupling mechanism in grain bulk,meanwhile,makes an analysis of grain temperature and moisture changes in the mechanical ventilation process,establishing a mathematical model of internal air flow and coupled heat and moisture transfer ingrain bulk.The experimental research of grain storage in small-scale test-warehouse within 1m~3 has been carried out,which makes a comparative analysis of numerical simulation and experimental results,verifying the rationality of mathematical model.Then,the grain stored in two selected warehouses in different areas has been taken as the object of study to carry out the numerical simulation and experimental research.The numerical simulation selects the atmosphere temperature and humidity and the daily local average of solar radiation as the boundary conditions,and selects the test temperature of real warehouse grain-feeling system and water condition as the initial condition,making a research on variation law of temperature and moisture in the process of natural storage and mechanical ventilation.At the same time,the temperature and humidity sensor in a barn is used to determine grain temperature in the process of grain natural storage and the mechanical ventilation.The numerical simulation and the measured results have been compared and analyzed through an in-depth analysis of the heat and moisture transfer law as well as the change law of temperature and moisture in grain bulk during the natural storage and mechanical ventilation process.The research has found: in the natural storage process,the external environment mainly affects the temperature of grain warehouse near the wall and the grain surface area in a slow and long way.As a result,the temperature in the grain bulk fluctuates with the environment temperature,but it will produce the temperature hysteresis due to the heat is transferred through the retaining structure of the warehouse.The internal temperature of grain bulk rises slowly because of the respiration of grain.In summer,the mildew is easily to occur because the temperature and moisture content are much higher at the surface of grain bulk.In winter,the temperature singularity is caused near the surface of the grain bulk at the south side of the wall,endangering the safety of grain storage.The warehouse mechanical ventilation can effectively reduce the grain temperature and the temperature gradient inside the grain bulk,thereby reducing the internal moisture migration rate of grain,in the meantime,during the grain mechanical ventilation process,there is severe coupled heat and moisture effect which will create temperature and water front in the grainbulk。Therefore,the numerical simulation research on a storage cycle of warehouse could effectively predict the change of temperature and moisture in grain bulk during the natural storage process to prevent mildew and offer a guidance for mechanical ventilation,ensuring the safety of grain storage.