Numerical Simulation Of Rough Rice Drying Process In A Deep Bed Under Angular Air Ducts

China is a large grain producing country,often ranking first in the world in grain production.In order to ensure safe storage of harvested grain,it must be dried to a safe moisture content before storage.Grain dryers are widely used in large production grain drying operations,and the core component of their heating section is the angular box of the drying section.At present,when the angular air ducts drying section is analyzed with finite element analysis,most of them only analyze its air flow field,and do not analyze the temperature and humidity field of the grain in combination with the deep bed drying model,and the physical field changes inside the grain are not analyzed in the deep bed drying analysis.Therefore,In this paper,a multi-physical field coupling simulation analysis of flow field,temperature field and humidity field is carried out for deep bed drying of rough rice under the angular air ducts as the research object.Based on this,the temperature,humidity and stress distribution inside the rough rice grain seeds during the drying process are investigated.After comparing and verifying the finite element simulation and experimental test data,the influence law of the angular box structure on the drying effect and the change law of temperature,moisture and stress during the drying process of rough rice seeds were investigated,which provide useful reference for optimizing the drying process and designing new grain dryers.The main research contents and conclusions of the whole paper are as follows:(1)The Ergun equation was used to calculate the pressure drop of rough rice grain pile,the local thermal non-equilibrium method to describe the heat transfer between the porous medium grain pile and air,and the thin layer equation to predict the moisture drop rate of rough rice seeds,based on which a mathematical model of deep bed drying in angular box was established.An angular box deep-bed drying device was built and drying tests were conducted.The reliability of the simulation results was verified by comparing the test with the simulation.And it was observed that the moisture content of paddy at the inlet and outlet after the drying was finished differed greatly,and the moisture content of paddy at the outlet hardly decreased,while the moisture content of paddy at the inlet was already close to the equilibrium moisture content.In the numerical simulation results of deep bed drying in the angular air ducts,it was found that the internal temperature change frontier of the grain pile reached the surrounding walls first,indicating that the conduction rate of temperature of the rough rice grain pile was greater than that of moisture.In addition,the temperature rise of rough rice grain and air with the slowest moisture drop at the corners.(2)The effects of different temperatures,different angular box arrangements,different angular box widths and whether the side walls of the angular boxes are open or not on the drying of grains were investigated.Under the condition of vertical arrangement of angular air ducts,the drying process was compared under the condition of 40℃,50℃,60℃ and 70℃ hot air,and the increase of hot air temperature can significantly increase the drying rate,but also significantly increase the temperature inhomogeneity coefficient.And the use of vertical arrangement of angular air ducts compared with parallel arrangement of angular air ducts,the use of hot air heat more fully,more rapid drying.The smaller width of the angular air ducts heats the top and bottom a little better,and the maximum temperature difference is smaller than the larger width of the angular air ducts.The hole on the side of the angular air ducts can improve the drying speed perpendicular to the side wall direction and reduce the drying speed below the side wall position.(3)In order to investigate the drying state inside the rough rice seeds during drying,the rough rice seeds were modeled as a three-layer ellipsoid consisting of rough rice husk,rough rice bran and endosperm,and a unidirectional hot air rough rice seed drying model was established and compared with the experimental results in the literature to verify the accuracy of the simulation model.The drying process of the rough rice seeds under the middle of the incoming air angular air ducts in the angular air ducts model was simulated under the unidirectional flowing hot air.The moisture distribution is symmetric along the short axis,while the temperature distribution is shifted along the wind direction.Although the hot air is variable temperature,the rough rice grain temperature always rises to a temperature close to the hot air temperature.Rough rice grain seed stress is closely related to the moisture gradient,and its maximum value increases and then decreases.