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

谷物冷却或干燥过程总是面临失败的风险，因为它依赖于天气。气流阻力不均匀会导致谷物在同一仓内的高气流位置过干，而在低气流位置过湿(变质)。影响气流阻力分布的两个主要因素是颗粒之间的孔结构(大小、形状、连通性、孔的曲折性和孔与气流方向的取向)和流体的性质(空气速度和粘度)。孔结构受籽粒大小、形状和对接数量、细小颗粒、异物和破碎籽粒(DFFB)的影响。已有的数学模型主要采用有限元方法来模拟空气流动阻力，并假定单元内部为连续介质，没有考虑DFB对孔结构的影响。因此，这些发展的模型没有考虑储粮散装内部的三维孔隙结构分布以及孔隙内的气流速度对气流阻力分布的影响。这导致预测精度较低。目前还没有建立谷粒内部孔隙结构的模型。用离散单元法(DEM)建立了孔隙结构模型。为了充分利用有限元方法和离散元方法的优点，提出了一种将有限元方法和离散元模型相结合的药物压片方法。在接下来的5年里，我将专注于通过建立三维孔结构DEM和考虑DFB对孔结构和气流阻力的影响的储粮堆内气流阻力分布有限元模型来填补这一空白。这两款车型将会结合在一起。为了验证所建立的模型，我建议测定不同含水率和DFFB下谷物的松散和压实孔隙率，模拟不同装载高度的储粮仓内DFFB的分布，并测量不同风速下储粮仓内的气流阻力分布。拟议的实验将使用新的技术来表征孔隙结构和测量空气流动阻力分布。拟议计划的长期目标是促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，本研究的结果不仅将为散装固体储存系统的设计和运行提供合理的分析工具，而且将有助于了解散装谷物的孔结构和流动的基础知识。所开发的气流分布模型将帮助设计工程师正确布置通风系统，并帮助粮主实施正确的通风策略。一名硕士、两名博士和五名本科生将通过这一拟议的计划接受培训。学生获得的知识和技能将有助于他们为在工业或学术界工作做准备。

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.***