基于孔隙尺度的大豆粮堆热湿耦合传递的研究

Study on coupled heat and moisture transfer in soybean grain pile based on pore scale

开展通风干燥过程中粮堆孔隙结构分布以及热湿耦合传递规律的研究,可为安全储粮以及干燥系统的设计提供理论依据。以大豆填充床为研究对象,基于局部质量和热量的非平衡原理,建立了大豆填充床通风干燥过程双扩散热湿传递模型。采用离散元法-有限容积法数值模拟了干燥条件下填充床内孔隙率、气流路径分布以及温度和水分耦合传递规律。结果表明:填充床的径向孔隙率呈振荡分布,近壁面孔隙率较大而填充床中轴线附近孔隙率较小,会使气流路径迂曲度呈现不规则分布;填充床的干燥速率主要受干燥空气温度和大豆颗粒含水量的影响;在干燥空气的相对湿度为17%及温度分别为35、45、55和65℃的条件下,前20 min填充床的干燥速率分别为0.077%/min、0.083%/min、0.089%/min和0.096%/min。

Studying the pore structure distribution of grain piles and heat-moisture coupling transfer in the process of drying can provide a theoretical basis for the design of safe grain storage and drying systems.In this study,the soybean packed bed is taken as the research object,and based on the principle of Local Mass and Thermal Non-Equilibrium(LMTNE),a double-diffusion heat and moisture transfer model is established during the drying process of the packed bed.Discrete element method and finite volume method are used to simulate and analyze the porosity and airflow path distribution of the packed bed,as well as the coupling transfer of temperature and moisture.The results indicate that the radial porosity of the packed bed exhibits an oscillating distribution.Due to the wall effect,the porosity near the wall is large but near the central axis is small,which resulted in the tortuosity of the airflow path present an irregular distribution.The double-diffusion heat and moisture transfer model is verified by using the experimental data.The drying rate of the soybean packed bed is mainly affected by the drying air temperature and the moisture content of soybean particles.At drying air temperature of 35,45,55 and 65℃,and relative humidity of 17%,the drying rates of the packed bed are 0.077%/min,0.083%/min,0.089%/min and 0.096%/min(within the first 20 minutes),respectively.