| The report of the 20th Party Congress proposed to "strengthen the foundation of food security in all aspects",and the post-production service of grain bears the important function of promoting grain upgrading,promoting grain saving and loss reduction,and improving farmers’ planting income,which plays an important role in guaranteeing national food security and supporting the high-quality development of grain industry.Through numerical simulation,we study the effect of heat and moisture migration pattern inside the grain pile under different tempering and ventilation conditions,which can provide data support for choosing efficiency tempering and ventilation methods and theoretical support for realizing green grain storage.Based on the theory of porous medium flow and heat and mass transfer,this topic establishes the mathematical model of heat and moisture coupling transfer in the process of stored grain ventilation,takes the corn grain pile in a large-span tall cottage silo as the research object,and uses the method of numerical simulation to study the regulation strategy and heat and moisture migration process of grain storage and quality control ventilation under different ventilation systems,and the main research contents and conclusions are as follows:1.Based on the theory of porous media flow and heat and mass transfer,the mathematical model was modified and improved,and the physical model of the experimental chamber was established.The simulation software was used to conduct numerical simulation research on the cooling and precipitation conditions of corn grain pile.Meanwhile,the cooling and precipitation ventilation experiment under the same conditions was carried out on the small experimental chamber,and the experimental data and simulation results were compared and analyzed to verify the accuracy of the mathematical model and the feasibility of the simulation.2.The simulation of four types of tempering ventilation,namely,cooling and cooling,heating and cooling,heating and cooling,and heating and cooling,is carried out for tall cottage silos with full-aperture ventilation system to study the heat and moisture migration law inside the corn grain pile,analyze the degree of cooling/warming corresponding to different tempering types under the same ventilation relative humidity difference,different ventilation relative humidity differences,and different tonnage ventilation conditions for each layer inside the grain pile.The simulation of the temperature and moisture content of the grain can provide data support for the selection of the optimal control strategy.It is found that for the full-aperture plate ventilation system,the temperature and moisture content changes inside the pile are less different along the length direction,so the two-dimensional physical model can be used instead of three-dimensional for numerical simulation,which saves calculation time and ensures the simulation results.Under the condition of poor ventilation relative humidity and the same ventilation volume per ton of grain,at the end of ventilation,the precipitation degree under the condition of heating and precipitation is better than that under the condition of cooling and precipitation,and the water increase degree under the condition of cooling and water increase is better than that under the condition of heating and water increase.3.Four types of conditioning ventilation simulations were conducted for a tall cottage bin with the above-ground ventilation cage ventilation system to study the changes of grain pile temperature and moisture content under different conditioning conditions with a ventilation relative humidity difference of 5%,an upward ventilation method and a ventilation volume of 30 m3/(h·t)ton of grain.It is found that there is a large gradient of temperature and moisture content inside grain piles along the length of grain silo in the ventilation system of ground ventilation cage,so it is not suitable to use two-dimensional physical model instead of three-dimensional model to carry out related research.The variation trend of water content in the ventilation cage system with different conditioning strategies is consistent with that in the ventilation system with full orifice plate.The unit energy consumption of warming precipitation conditioned ventilation is 0.19 kw·h/(1%moisture·t)lower than that of cooling precipitation,and the unit energy consumption of cooling water conditioned ventilation is 0.08 kw·h/(1%moisture· t)lower than that of warming water conditioned ventilation. |
