多孔介质内颗粒流动特性的格子Boltzmann模拟

地下岩石孔隙中小颗粒的运移和沉积会使得储层渗透性能降低,影响石油开发。为了探究悬浮颗粒在多孔介质中的流动过程,采用格子Boltzmann方法对三维多孔介质内流体和颗粒的运动过程进行了数值模拟,采用有限体积颗粒法构建多孔介质中骨架颗粒和悬浮颗粒。通过Half-Way反弹格式实现流体与颗粒间的相互作用,考虑孔隙结构、入口流速、孔隙率和颗粒直径对颗粒流动特性的影响,探究颗粒的运移和沉积规律。结果表明,入口速度对不同孔隙结构下颗粒的运动作用显著。随着入口速度增大,颗粒与颗粒、孔隙壁面以及流体之间的动量和能量交换作用增强,缩短了颗粒的运移路径,颗粒沉积率逐渐变小,颗粒拟温度增大。孔隙率的下降强化了颗粒间的碰撞,孔隙率由0.581降低至0.400,使得颗粒拟温度提升至9倍。颗粒拟温度随颗粒直径的增加而增加。但随着孔隙率增加,颗粒轴向速度增加,颗粒最高轴向速度可达入口流速的11倍,而颗粒接触力降低。     

分形多孔介质传热传质过程的格子Boltzmann模拟

针对自然界中实际多孔介质具有的分形特性和随机性,利用中点替代算法和二值化处理构造统计上具有分形特性的随机多孔介质。分析了所构造的多孔介质盒维数与Hurst指数之间的关系。基于随机分形构造的原理,对二维实际多孔介质图像进行了重构。利用两点相关函数,分析了重构图像的结构相关性, 并与实际目标多孔介质的结构特征进行比较。在与解析解对比验证的基础上,将基于二元混合理论的格子Boltzmann模型（LBM）用于模拟多孔介质内流体扩散过程。通过计算不同分形特性的二维多孔介质的有效扩散系数,研究了重构多孔介质的分形维数与有效扩散系数的关系。利用热耦合LBM模型计算多孔介质内传热过程,分析了不同的分形特性对多孔介质蓄热过程的影响。     

Effect of non‐isothermal condition on heterogeneous flow through biofilter media by lattice Boltzmann simulation

BACKGROUND: Biofiltration technology has received much attention due to its effectiveness, low cost and environment friendly properties. It is used to remove odors caused chiefly by hydrogen sulfide (H2S) via biological treatments. RESULTS: In this study, numerical simulations using the thermal lattice Boltzmann method are implemented to investigate the effect of non‐isothermal conditions on heterogeneous flow through three biofilter models that are partly filled with porous media. The generalized Navier–Stokes model based on the Brinkman‐Forchheimer–extended Darcy model is used to make several assumptions. CONCLUSIONS: The numerical results indicate that the Rayleigh number has significant influence on the removal efficiencies of biofilters. There also exist critical Rayleigh numbers for biofilters under non‐isothermal conditions. If the Rayleigh number is less than the critical value, the flow heterogeneity will reduce with increasing Rayleigh number; otherwise, the flow heterogeneity will enhance with increasing Rayleigh number. Moreover, it was found that the performances of biofilters can be improved by designing non‐isothermal conditions between the porous media layers, i.e. by adjusting the Rayleigh number to optimize the detention time of waste air. © 2012 Society of Chemical Industry     

多孔介质内流体流动的格子Boltzmann模拟

采用格子Boltzmann方法模拟多孔介质内的流动过程,通过预测渗透率,比较了单松弛模型、多松弛模型和熵格子模型在多孔介质计算中的优劣,为研究多松弛模型中各自由参数的影响,选择了12种组合进行模拟,此外,还将大涡模拟与格子Boltzmann方法相结合模拟了多孔介质内高Reynolds数下的流动及流型的转变。结果表明：单松弛模型和熵格子模型预测的渗透率随黏度逐渐增大,而多松弛模型得到的结果随黏度变化很小,另外,多松弛模型中不同松弛参数的组合对结果有较大的影响,通过比较推荐了模拟多孔介质时的最佳组合,计算结果与经验公式吻合较好。大涡模拟与多松弛模型结合较好地预测了多孔介质内流型的转变,Reynolds数越大,多孔介质内的涡越多,并且变大。     

功能性多孔介质中气泡输运调控的格子Boltzmann分析

为提高毛细蒸发海水淡化技术中的蒸发效率,多孔介质层需要维持一定的毛细压力,同时还要确保气泡能够快速通过。基于此背景,本文建立了多孔介质参数化模型,探究了气泡穿越多孔介质间隙过程的运动特征,研究在保持一定孔隙毛细压力的同时,通过调控孔道尺寸及排布从而使气泡能够更快速地通过多孔介质层。基于格子Boltzmann伪势模型分析了多孔介质孔隙率、壁面润湿特性、孔道排布及气泡水平方向初速度等对气泡形貌、上升速度、与壁面平均接触面积及孔隙毛细力的影响,获得了多孔介质的孔隙率设计范围,骨架润湿特性调控以及孔道排布方式的选择依据。同时还获得了在实际蒸发过程中,可以使气泡存在一定的水平方向初速度,从而能够更快地脱离多孔介质的策略。     

多孔介质的孔隙特性对气体扩散过程影响的直接数值模拟

引言多孔介质内的扩散过程广泛存在于化工、能源、环境和生物等领域,例如石油天然气开采、污水处理、填充床化学反应、催化剂和生物组织内的质量传递等,使得多孔介质内传质现象的研究尤为重要[1-2]。多孔介质由于结构和形状各异,难以有准确、有效且简单的描述方法,因而研究变得极为     

格子Boltzmann方法模拟高Darcy数多孔介质内融化传热过程

采用Brinkmann-Forchheimer-Darcy方程描述多孔介质内流动过程,并通过选择合适的平衡态分布函数及非线性源项形式构建出表征融化相变温度场的分布函数演化方程。应用格子Boltzmann模型模拟了方腔内无多孔介质以及填充多孔介质自然对流融化传热过程,模拟结果与其他文献结果吻合较好,模型的正确性得到了一定的验证。模拟结果还表明液相的自然对流对融化传热过程有着重要的影响,并且在高Rayleigh 数或高Darcy 数情况下作用更强。在高Darcy 数情况下由于非Darcy效应的存在,增大Rayleigh 数以强化融化传热的效应要大于提高同样倍数Darcy 数的效应。     

Three‐dimensional simulations of biofilm growth in porous media

Biofilm growth occurs in a variety of random porous media in a range of industrial processes; prediction of its growth and subsequent influence on hydrodynamics is hence desirable. In this study, we present the first numerical 3D pore‐scale model of biofilm growth in porous media, based on a lattice Boltzmann simulation platform complemented with an individual‐based biofilm model (IbM). We use it to explore the coupled interaction between nutrient mass transport, biofilm growth, and hydrodynamics. Biofilm is shown to be very effective at reducing the permeability of porous media, particularly under nutrient limited conditions. We conclude with a direct comparison of 3D and 2D biofilm growth simulations in porous media and show the necessity of performing the simulations in 3D. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

REV尺度多孔介质格子Boltzmann方法的数学模型及应用的研究进展

综述了多孔介质表征体元尺度(REV)格子Boltzmann模型的研究进展,根据对多孔介质处理方式主要分为部分反弹模型和阻力模型两类,分析归纳了各类模型的优缺点。由于阻力模型中渗流的广义格子Boltzmann方程(GLBE)的作用力是基于GUO等的作用力模型,可以准确得到宏观方程,不存在离散误差,且模型的平衡分布函数和作用力项中都包含反应介质特性的孔隙率,因而应用最为广泛。本文还重点介绍了REV尺度多孔介质LBE模型在流动、传热、传质、化学反应及相变等过程中的具体应用,认为REV尺度多孔介质内的三传一反数学模型中需要加入孔隙尺度因素,在更大工程尺度上应该考虑过程参数的各向异性,展望了REV尺度多孔介质LBE模型的发展和应用前景。     

Lattice Boltzmann simulation of asymptotic longitudinal mass dispersion in reconstructed random porous media

To research macroscopic mass transport characteristics of porous media, a lattice Boltzmann method (LBM) approach was utilized to calculate asymptotic longitudinal mass dispersion. In this study, a D2Q9 model with multi‐relaxation‐time (MRT) collision operator, which is appropriate for incompressible flow with a high Péclet number without refining the lattice, was chosen. With respect to the microstructure of porous media, random placement (RP) method was applied to obtain randomly positioned particles. Based on the exhausted numerical results presented in the study, a new correlation of longitudinal mass dispersion was established. By comparing with available experimental data in the literature, reasonable agreements are observed in a wide porosity range from 0.3 to 0.7, indicating the validity of the proposed correlation. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2770–2780, 2018     

Synthesis and characterization of poly(hydroxamic acid) chelating resin from poly(methyl acrylate)‐grafted sago starch

A new chelating ion‐exchange resin containing the hydroxamic acid functional group was synthesized from poly(methyl acrylate) (PMA)‐grafted sago starch. The PMA grafted copolymer was obtained by a free‐radical initiating process in which ceric ammonium nitrate was used as an initiator. Conversion of the ester groups of the PMA‐grafted copolymer into hydroxamic acid was carried out by treatment of an ester with hydroxylamine in an alkaline solution. The characterization of the poly(hydroxamic acid) chelating resin was performed by FTIR spectroscopy, TG, and DSC analyses. The hydroxamic acid functional group was identified by infrared spectroscopy. The chelating behavior of the prepared resin toward some metal ions was investigated using a batch technique. The binding capacities of copper, iron, chromium, and nickel were excellent and the copper capacity was maximum (3.46 mmol g⁻¹) at pH 6. The rate of exchange of the copper ion was very fast that is, t_1/2 < 5 min. It was also observed that the metal ion‐sorption capacities of the resin were pH‐dependent and its selectivity toward the metal ions used is in the following order: Cu²⁺ > Fe³⁺ > Cr³⁺ > Ni²⁺ > Co²⁺ > Zn²⁺ > Cd²⁺ > As³⁺ > Pb²⁺. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1256–1264, 2001     

Lattice Boltzmann simulation of biofilm clogging and chemical oxygen demand removal in porous media

Understanding mechanisms of controlling the bacteria growth and degradation of pollutants is critical for effective improvements in water treatment and bioremediation in porous media. In this study, we developed an integrated model of individual-based model and multicomponent lattice Boltzmann method to study interactions of oxygen, bioclogging, chemical oxygen demand (COD) removal, and their influence on growth and permeability of microbial biofilms. We found biofilm growth to be very heterogeneous on the surface of the solid matrix and pores. There is a biofilm porosity threshold. Beyond this threshold, the porosity of biofilm has no obvious influence on the flow rate and COD removal. We also studied the influence of initial cell populations, bulk oxygen concentration and biofilm permeability on the flow rate and COD removal. It demonstrated the capability of the present model to investigate biofilm growth, clogging and contaminants degradation in porous media, and its potential applications in water treatment.     

Pore scale inertial flow simulations in 3‐D smooth and rough sphere packs using lattice Boltzmann method

Pore‐scale inertial flows in periodic body centered cubic (BCC) arrays of smooth and rough sphere packs were simulated using lattice Boltzmann method. Computed velocity fields were visualized and averaged to calculate macroscopic flow parameters characteristic of porous media such as permeability, tortuosity, and β factor as well as the transition Reynolds number values and compared well with established correlations. Furthermore, hemispherical depositions on the smooth spheres in the regular BCC array were used to calculate roughness induced changes in macroscopic flow parameters. As the next step toward simulating inertia dominated flow in natural porous media, simulations were validated for low Reynolds number flow in a three‐dimensional (3‐D) CT image of irregular pack of uniform diameter spheres. This work aims to define 3‐D canonical studies for roughness induced inertial flows in porous media and to assess the capability of LBM for simultaneous prediction of absolute permeability and β factor. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4858–4870, 2013     

Mixing induced by buoyancy‐driven flows in porous media

A theoretical model for fluid mixing in steady and transient buoyancy‐driven flows induced by laminar natural convection in porous layers is presented. This problem follows a highly nonlinear dynamics and its accurate modeling poses numerical challenges. Based on the Taylor dispersion theory, a one‐dimensional analytical model is developed for steady and transient velocity fields. To investigate steady‐state mixing, a unicellular steady velocity field is established by maintaining a thermal gradient across a porous layer of finite thickness. A passive tracer is then introduced into the flow field and the mixing process is studied. In the case of transient flows, as the convective flow grows and decays with time the behavior of the dispersion coefficient is characterized by a four‐parameter Weibull function. The simple analytical model developed here can recover scaling relations that have been reported in the literature to characterize the mixing process in steady and transient buoyancy‐driven flows. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1378–1389, 2013     

Preparation and characterization of poly(methyl methacrylate) grafted sago starch using potassium persulfate as redox initiator

In this article, the graft copolymerization of methyl methacrylate (MMA) onto sago starch (AGU) was carried out in aqueous medium using potassium persulfate (PPS) under nitrogen gas atmosphere. The maximum percentage of grafting achieved was 90% under optimized conditions of reaction temperature, monomer, PPS, AGU, and reaction period corresponding to 50°C, 47 mmol, 1.82 mmol, 6.17 × 10^?3 mol L^?1, and 1.5 h, respectively. The grafting of MMA onto sago starch was confirmed by the differences in infrared spectroscopy. The viscosity measurement and the average molecular weight determination were estimated using Huggin's and Mark Houwink's equations, respectively. This material may have application as a biodegradable plastic. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1891–1897, 2004     

Numerical simulation of viscous fingering of shear‐thinning fluids

The viscous fingering instability of miscible shear‐thinning fluids has been examined using a pseudo‐spectral numerical technique based on the Hartley transform. The instability was studied for a flow in a rectilinear Hele‐Shaw cell, and the shear‐thinning character of the fluids has been modelied using the Carreau equation. New mechanisms of viscous fingering not previously observed in the case of similar Newtonian flow displacements have been identified. These mechanisms, which are reminiscent of the fractal patterns observed in experimental studies, were interpreted in terms of the velocity‐dependent mobility of the flow.     

Flow of mixtures of poly(ethylene oxide) and hydrolyzed polyacrylamide solutions through porous media

In this work, the porous media flow of polymer solutions of poly(ethylene oxide) (PEO), hydrolyzed polyacrylamide (HPAA), and their blends is investigated. Aqueous solutions of PEO exhibit critical extension thickening when flowing through porous media. HPAA solutions also exhibit critical extension thickening in excess salt environments, but their behavior changes to a more gradual extension thickening when dissolved in deionized water. The mixtures of solutions of HPAA and PEO therefore vary its porous media flow behavior, depending on the ionic environment. In deionized water, a critical extension thickening similar to that obtained with PEO is still observed when HPAA is mixed in at concentrations low enough so that its apparent viscosity does not mask the influence of PEO. In the presence of salt, only a critical extension thickening is observed, which is attributed to transient network formation of both PEO and HPAA molecules. The mixtures generally exhibit a less critical behavior and display a lower than expected sensitivity of the onset Reynolds number for extension thickening with concentration. The results presented herein indicate that interspecies molecular interactions through transient network formation and the associated flow modification play a major role in determining the complex non‐Newtonian flow behavior of these polymer solutions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 783–795, 1999