仓储粮堆三维非规则孔道网络模型的优化研究

Construction and optimization of 3D pore network model in bulk grain pile

为了更详尽地反映仓储粮堆内部粮食颗粒与孔喉之间、孔隙与孔隙之间的位置关系,更合理地描述仓储粮堆内部在机械通风过程中的湿热传递规律,利用三维CT扫描设备与Avizo软件对颗粒堆积样件的孔喉进行提取,获得颗粒堆积样件实际三维孔道网络模型。其中喉道长度主要分布在6.0~14.0 mm之间,大约占喉道总数的96%,喉道长度分布大致为Poisson分布;孔隙半径多在2.0~10.0mm之间。通过EDEM软件模拟粮食颗粒堆积状态,基于泰森多边形原理,通过voro++软件处理堆积体中的颗粒坐标及半径等参数,结合孔隙划分规则对不合理孔隙进行处理,获得仓储粮堆三维非规则孔道网络模型。其中孔隙配位数主要集中在3、4、5和6,喉道长度主要分布在3.0~13.0 mm之间,孔隙半径分布大致在2.0~10.0 mm之间,三者均大致呈Poisson分布;颗粒配孔数在7~18之间,颗粒配喉数在4~20之间,其中大部分配孔数集中在8~16之间。软件构建所得的三维孔道网络模型可以描述仓储粮堆内部孔隙结构,且构建所得结构参数较Avizo软件提取获得的结构参数更加全面,更能准确地描述仓储粮堆内部颗粒、孔隙以及喉道之间的关系。

Grain pile is a kind of non-consolidated hygroscopic porous medium and its internal pore structure is complex and diverse.During the drying and storage of grain pile,the heat and mass transfer inside the grain pile mainly occurs in the pore space surrounding grain particles and the interface between pores and particles.The simulation results of traditional model based on the "continuous medium hypothesis" can reflect a general trend of heat and mass transfer rather than the transfer phenomenon between particles and pores.In fact,the simulation results of heat and mass transfer between particles is far from the actual drying conditions.In detail,no difference is found between the state parameters of pores and particles,which is inconsistent with the actual situation during the drying process of grain pile.In order to determine the positional relationship of skeletons and pores in the unconsolidated porous medium more accurately,and describe the heat and mass transfer of unconsolidated porous medium during the ventilation process more reasonably,an irregular pore network model was constructed to describe the internal structure of grain pile.First of all,3 D CT scanning equipment and Avizo software was used to extract the pore throat of the particle accumulation sample.It was found that the length of the throat is mainly distributed between 6.0 and 14.0 mm,accounting for about 96% of the total throats,and the distribution of throat length roughly fits Poisson distribution;the pore radius is mostly between 2.0 and 10.0 mm.Secondly,according to the principle of Tyson polygonal structure,the natural accumulation process of grain particles was simulated by EDEM software.The particle information was processed by voro++software.Combined with the pore division rules,some obtained pores were merged to optimize the pore network.The three-dimensional irregular pore network physical model was built to describe the pore structure of grain pile.The pore coordination number is mainly concentrated in 3,4,5 and 6,the throat length is mainly between 3.0 mm and13.0 mm,the pore radius is roughly between 2.0 mm and 10.0 mm,and the three parameters roughly fit Poisson distribution.The results also showed that the obtained structural parameters are more exhaustive than that of Avizo software.The three-dimensional irregular pore network physical model is able to describe the relationship between particles,pores and throats in the storage grain pile more precisely.