Three dimensional models of pore structure and airflow distribution inside grain bulks

谷物冷却或干燥过程由于其对天气的依赖性而总是有失败的风险。不均匀的气流阻力导致在同一仓内的高气流位置处的过干谷物和低气流位置处的湿（变质）谷物。影响气流阻力分布的两个主要因素是谷粒之间的孔隙结构（孔隙的大小、形状、连通性、弯曲度以及孔隙相对于气流方向的取向）和流体的性质（空气速度和粘度）。孔结构受籽粒大小、形状以及堵塞物、细粒、异物和破碎籽粒（DFFB）的量的影响。已有的数学模型主要采用有限元法模拟气流阻力，并假设单元内部为连续体，没有考虑DFFB对孔隙结构的影响。因此，这些模型没有考虑三维孔隙结构的分布和孔隙内的空气流速对气流阻力分布的影响。这导致预测准确度较低。没有模型的孔隙结构内的粮食散装已开发。可以通过使用离散单元法（DEM）来开发孔隙结构模型。为了充分利用有限元法和离散元法的优点，提出了一种联合收割机有限元法和离散元法相结合的方法。在未来5年中，我将致力于通过开发三维孔隙结构DEM和考虑DFFB对孔隙结构和气流阻力的影响的储粮散装内部气流阻力分布有限元模型来填补这一空白。这两种模式将结合在一起。为了验证这些开发的模型，我建议确定松散和压实的粮食在不同的水分含量和DFFB的孔隙率，模拟不同装载高度的仓内DFFB的分布，并测量在不同的空气速度下的粮仓内的气流阻力分布。该实验将使用新技术来表征孔隙结构和测量气流阻力分布。该计划的长期目标是推进散装固体系统的知识，并将其应用于储存谷物生态系统。 因此，本研究的结果将不仅提供一个合理的分析工具，散装固体存储系统的设计和操作，但也有助于通过粮食散装孔隙结构和流动的基础知识。所建立的气流分布模型可帮助设计工程师正确布置通风系统，也可帮助粮商制定合理的通风策略。一个硕士，两个博士和五个本科生将通过这个拟议的计划进行培训。学生获得的知识和技能将有利于他们在工业或学术界工作。*

The grain cooling or drying process is always at risk of failure because of its weather dependency. The non-uniform airflow resistance results in over-dried grain at high airflow locations and wet (spoiled) grain at low airflow locations inside the same bin. The two major factors influencing the airflow resistance distribution are the pore structure among grain kernels (size, shape, connectivity, tortuosity of the pores, and orientation of the pore to the airflow direction) and properties of fluids (air velocity and viscosity). The pore structure is influenced by kernel size, shape, and amount of dockage, fines, foreign materials and broken kernels (DFFB). Published mathematical models mainly used Finite Element Method (FEM) to simulate airflow resistance and assumed continuum inside each element without considering the effect of DFFB on pore structure. Therefore, these developed models did not consider 3D pore structure distribution inside stored grain bulks and the effect of air velocity inside pores on airflow resistance distribution. This results in low prediction accuracy. No model of pore structure inside grain bulks has been developed. A pore structure model can be developed by using Discrete Element Method (DEM). To take advantage of both the FEM and DEM methods, a method to combine FEM and DEM model has been developed for pharmaceutical tableting. In the next 5 years, I will focus on objectives to fill this gap by developing 3D pore structure DEM and airflow resistance distribution FEM models inside stored grain bulks by considering the effect of DFFB on pore structure and airflow resistance. These two models will be coupled together. To validate these developed models, I propose to determine loose and compacted porosity of grains at different moisture contents and DFFB, to model the distribution of DFFB inside bins with different loading heights, and measure airflow resistance distribution inside grain bins under different air velocities. The proposed experiments will use novel technique to characterize pore structures and measure air flow resistance distribution.The long term objective of the proposed program is to advance the knowledge of bulk solid systems with applications to stored grain ecosystems. Therefore, the results from this proposed research will not only provide a rational analysis tool for the design and operation of bulk solid storage systems, but also contribute to the fundamental knowledge of pore structure and flow through grain bulks. The developed airflow distribution model will help design engineers to lay out the aeration system correctly and grain owners to conduct a right ventilation strategy. One MSc, two PhD and five undergraduate students will be trained through this proposed program. The knowledge and skills acquired by students will be beneficial to them in preparing them to work in industry or academia.***