Willingham Thomas W, Werth Charles J, Valocchi Albert J
Department of Civil and Environmental Engineering, University of Illinois Urbana-Champaign, Urbana Illinois, USA.
Environ Sci Technol. 2008 May 1;42(9):3185-93. doi: 10.1021/es7022835.
The objectives of this work were to determine if a pore-scale model could accurately capture the physical and chemical processes that control transverse mixing and reaction in microfluidic pore structures (i.e., micromodels), and to directly evaluate the effects of porous media geometry on a transverse mixing-limited chemical reaction. We directly compare pore-scale numerical simulations using a lattice-Boltzmann finite volume model (LB-FVM) with micromodel experiments using identical pore structures and flow rates, and we examine the effects of grain size, grain orientation, and intraparticle porosity upon the extent of a fast bimolecular reaction. For both the micromodel experiments and LB-FVM simulations, two reactive substrates are introduced into a network of pores via two separate and parallel fluid streams. The substrates mix within the porous media transverse to flow and undergo instantaneous reaction. Results indicate that (i) the LB-FVM simulations accurately captured the physical and chemical process in the micromodel experiments, (ii) grain size alone is not sufficient to quantify mixing at the pore scale, (iii) interfacial contact area between reactive species plumes is a controlling factor for mixing and extent of chemical reaction, (iv) at steady state, mixing and chemical reaction can occur within aggregates due to interconnected intra-aggregate porosity, (v) grain orientation significantly affects mixing and extent of reaction, and (vi) flow focusing enhances transverse mixing by bringing stream lines which were initially distal into close proximity thereby enhancing transverse concentration gradients. This study suggests that subcontinuum effects can play an important role in the overall extent of mixing and reaction in groundwater, and hence may need to be considered when evaluating reactive transport.
这项工作的目标是确定孔隙尺度模型能否准确捕捉控制微流体孔隙结构（即微观模型）中横向混合和反应的物理和化学过程，并直接评估多孔介质几何形状对横向混合受限化学反应的影响。我们将使用格子玻尔兹曼有限体积模型（LB-FVM）的孔隙尺度数值模拟与使用相同孔隙结构和流速的微观模型实验进行直接比较，并研究粒径、颗粒取向和颗粒内孔隙率对快速双分子反应程度的影响。对于微观模型实验和LB-FVM模拟，两种反应性底物通过两条独立且平行的流体流引入孔隙网络。底物在垂直于流动方向的多孔介质内混合并发生瞬时反应。结果表明：（i）LB-FVM模拟准确捕捉了微观模型实验中的物理和化学过程；（ii）仅粒径不足以量化孔隙尺度的混合；（iii）反应性物质羽流之间的界面接触面积是混合和化学反应程度的控制因素；（iv）在稳态下，由于聚集体内部相互连通的孔隙率，混合和化学反应可在聚集体内部发生；（v）颗粒取向显著影响混合和反应程度；（vi）流动聚焦通过使最初相距较远的流线靠近从而增强横向浓度梯度来增强横向混合。这项研究表明，亚连续效应可能在地下水混合和反应的总体程度中起重要作用，因此在评估反应输运时可能需要考虑。
