| Without food security,there is no national security.In order to ensure food security in our country,on the one hand,we must increase food production,on the other hand,we must strengthen food reserves.Most of China’s existing grain storage warehouses have shortcomings such as low land utilization and high energy consumption.The use of underground storage grain can not only effectively save land resources and achieve multi-use in one place,but also effectively use natural ground temperature to achieve long-term low temperature(≤15℃)or quasi-low temperature storage grain(≤20℃)on the basis of low energy consumption or even zero energy consumption.,Reduce the use of drug fumigation,thereby achieving green grain storage.The underground granary is placed underground for a long time.In order to exclude the influence of groundwater and maintain the storage environment dry,two methods of structural waterproofing and additional waterproofing are generally adopted to solve the problem of waterproof and moisture resistance.However,in the two new types of additional waterproofing methods,dew condensation may occur where the inner lining steel plate and the inner lining plastic plate contact the food.Because the grain temperature in the core is high during the grain storage in the underground warehouse,the grain temperature close to the warehouse wall is low.The heat is spontaneously transferred from the high temperature part of the core of the grain pile to the low temperature wall surface,and the relative humidity of the air between grains and grains is changed with the heat transfer.The moisture content of the air next to the silo wall increases,and condensation will occur at the silo wall when the silo wall temperature is lower than the corresponding air dew point.Condensation causes the grains to increase respiration,heat,sprout and then mildew,which poses a hidden danger to the safety of grain storage.Therefore,solving the problem of dew condensation on the wall surface in underground storage grain is the key to guarantee the quality of underground storage grain.When using grain storage in the ground,the temperature of grain during storage is directly affected by the ambient temperature in the warehouse,and the environment in the warehouse is closely related to the outdoor environment.Influence of soil temperature.Compared with air,although the thermal physical properties of the soil have thecharacteristics of large heat capacity and strong thermal inertness,this transmission process through "environmental temperature affects silo temperature and silo temperature affects grain temperature" exists objectively.To explore the change rule of the temperature of the grain pile in the silo after the heat transfer through the wall and the top of the grain pile under the influence of the soil temperature in the underground silo system.The temperature of the underground soil changes with depth.It is of great significance to analyze the affected area and range to make better use of the thermal characteristics of the underground soil and determine the most favorable stratum depth range.In this paper,to solve the problem of grain condensation on the wall of the silo under the condition of non-manual intervention in the storage of the underground grain silo,an underground silo simulation experiment platform was built,and different waterproof materials with the same thickness(lined plastic plate,lined steel plate)were used in the set control experimental silo),Through the multi-channel data recorder to record the change law of the temperature field and humidity field of the wheat grain pile in the experimental warehouse during storage.The experiment time starts from September 24,2019 to ends on January 12,2020,and includes three consecutive changes in the external environment of grain storage in autumn,autumn and winter transition season,and winter;analyze the condensation of different lining waterproof materials on the inner wall of the underground warehouse The experiment shows that the temperature distribution of the upper part of the grain pile is affected by air temperature,and the lower part depends on the temperature level of the constant temperature zone.The overall trend is similar to that of the above-ground storage warehouse.Based on the COMSOL simulation platform,an experimental warehouse model was built to simulate the experimental storage process.The average relative error between the simulation and the experiment was 7.9%.The research was extended based on the design plan of the actual underground warehouse to prevent condensation.The simulation showed that the top of the actual warehouse was 0m above the ground.Determine the most suitable opening depth within the range of 0m-4m.The burial depth has little effect on the grain temperature at the core of the grain pile and near the bottom of the silo.The temperature has the greatest influence on the temperature of the upper layer of the grain pile.The temperature difference between the upper layer and the grain at the depth of 1m and 4m is about 3℃.The influenceof the water is gradually weakened,and it tends to be stable from a burial depth of 3.5m,which is the shallowest burial depth to isolate the influence of outside air temperature;under non-manual intervention conditions(such as mechanical ventilation),the temperature of the grain into the warehouse and the ambient temperature When they are consistent,it is necessary to determine a better time to enter the position.Because the porous medium of the grain pile is a poor conductor of heat,the temperature of the core of the grain pile drops slowly.The lower the grain temperature when entering the warehouse,the more beneficial it is for grain preservation.The simulation results show that the subsequent artificial refrigeration can be reduced under the condition of entering the grain temperature at 28℃.Use,to determine the better time to enter the warehouse is from autumn to spring.If high-temperature and high-moisture grains enter the warehouse,they need to be ventilated and cooled first.When the grain temperature is reduced to 28℃ and the air humidity is below50%,it is safer to use the ground temperature to store grain;in the simulation,the wall-attaching material is changed,and the steel plate and plastic are used Board,red brick.The simulation results show that the material with good thermal conductivity is conducive to the temperature reduction in the warehouse.After 30 days of storage,the grain temperature at the liner steel plate is 0.33℃ lower than the grain temperature at the liner plastic plate.The steel plate is used as the waterproof material for the underground lining.Provide a reference for the anti-condensation design on the inner wall of the actual underground warehouse. |
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