微流控器件中的多相流动

微流控技术及微流控器件是近年来发展迅速的多学科交叉研究领域.相比于传统方法, 微流控技术能够实现对微量多相流体的精准操控, 可应用于化学分析、先进材料合成、蛋白质结晶、单细胞培育及检测、信息处理等领域. 该文回顾微流控器件中的多相流动现象, 概述其所涉及的流体力学机理,阐述实现多相微流控的各种方法, 并分析多相微流控技术的应用现状及面临的挑战, 最后总结针对多相微流动问题的数值模拟方法和实验测量技术, 展望多相微流控器件的研究方向及应用前景.      

Bounding Envelopes in Multiphase Material Design

In practice, whenever determining macroscopic effective mechanical properties of materials possessing irregular heterogeneous microstructure, one can only test, numerically or experimentally, finite sized samples. Such materials are exemplified by randomly distributed particles suspended in a homogeneous binding matrix. If one were to compute the effective responses of various equal finite sized samples, with the only mutually distinguishing feature being the various random distributions of the particulate matter, fluctuations would occur. While such fluctuations can be small for large samples, their effects become amplified when computing design sensitivities, such as gradients and Hessians, for macroscopic effective property optimization strategies. Concisely stated, these fluctuations can severely impair the performance of such approaches by destroying the quality of the derivatives. A natural way of eliminating the negative effects of such fluctuations is by ensemble averaging the response of multiple samples until the results stabilize, and then to construct the sensitivities with the stabilized results. The focus of this work is to interpret such an ensemble regularization process, in particular when it is incorporated into effective property design procedures. It is shown that, under certain conditions, this type of regularization produces upper and lower bounding envelopes for objective functions representing desired macroscopic effective responses associated with idealized, fluctuation free, material samples of infinite size.     

Nonequilibrium Effects and Multiphase Flow in Porous Media

In this paper we develop a more general formulation for transient multiphase flow in porous media based on physics observed in core-scale and micromodel experiments. We account for non-equilibrium effects by considering redistribution time and treat saturation by evolving locally moving time-averages of the saturation. Several families of models arise from approximations to the general formulation with various degrees of accuracy. The classical Buckley-Leverett and Barenblatt expressions are special cases of these families. We explore the behaviors of a number of special cases arising from the proposed general formulation using established and novel numerical schemes that provide nonlinear physics-based preconditioning. The agreement observed between numerical and experimental results demonstrates the consistency of the proposed abstraction.     

Analysis of Multiphase Non-Darcy Flow in Porous Media

Recent laboratory studies and analyses (Lai et al. Presented at the 2009 Rocky Mountain Petroleum Technology Conference, 14–16 April, Denver, CO, 2009) have shown that the Barree and Conway model is able to describe the entire range of relationships between flow rate and potential gradient from low- to high-flow rates through porous media. A Buckley and Leverett type analytical solution is derived for non-Darcy displacement of immiscible fluids in porous media, in which non-Darcy flow is described using the Barree and Conway model. The comparison between Forchheimer and Barree and Conway non-Darcy models is discussed. We also present a general mathematical and numerical model for incorporating the Barree and Conway model in a general reservoir simulator to simulate multiphase non-Darcy flow in porous media. As an application example, we use the analytical solution to verify the numerical solution for and to obtain some insight into one-dimensional non-Darcy displacement of two immiscible fluids with the Barree and Conway model. The results show how non-Darcy displacement is controlled not only by relative permeability, but also by non-Darcy coefficients, characteristic length, and injection rates. Overall, this study provides an analysis approach for modeling multiphase non-Darcy flow in reservoirs according to the Barree and Conway model.     

Electrical Resistivity Index in Multiphase Flow through Porous Media

The simultaneous flow of two phases through a three-dimensional porous medium is calculated by means of a Lattice-Boltzmann algorithm. The time-dependent phase configurations can be derived and also macroscopic quantities such as the relative permeabilities. When one phase only is supposed to be conductive, the Laplace equation which governs electrical conduction can be solved in each phase configuration; an instantaneous value of the macroscopic conductivity is obtained and it is averaged over many configurations. The influence of saturation on the resistivity index is studied for six different samples and two viscosity ratios. The saturation exponent is systematically determined. The numerical results are also compared to other possible models and also to experimental results; finally, they are discussed and criticized.     

Multiphase laminates of extremal effective conductivity in two dimensions

This paper deals with two-dimensional composites made of several isotropic linearly conducting phases in prescribed volume fractions. The primary focus is on the three-phase case; the generalization to a larger number of phases is straightforward.A class of high- but finite-rank laminates is introduced. The laminates saturate the known inequality bounds—due to the work of Hashin and Shtrikman, Lurie and Cherkaev, Tartar, and Murat and Tartar—on the effective conductivity tensor of any composite. These bounds depend only on the constituent material properties and volume fractions and not on the placement of these materials in the composite. The bounds are known not to be optimal for all admissible choices of the conductivities and volume fractions. However, they are now known to be realizable in a much larger range of these parameters than was previously known.The range of effective properties of our multiphase laminates strictly includes those corresponding to the composites found earlier by Milton and Kohn, Lurie and Cherkaev, and Gibiansky and Sigmund. The new optimal laminates are found in a systematic fashion by satisfying sufficient conditions on the fields in each layer. This leads to a simple algorithm for generating optimal laminates.In addition a new supplementary bound for multiphase structures is also proven which must be satisfied by composites with smooth interfaces.     

明渠效应在多相计量中的应用研究

在多相流体力学和多相流测量方面大量的基础理论研究和实验研究的基础上,提出了全新的明渠流模型等多个流量计测模型用于多相流量计量。通过自主开发的智能型多相流量计测系统在室内多相流测试环道上,对模型的运用效果做了大量的实验研究。并且利用基于神经网络技术和模糊模式识别技术开发的计测软件对实验数据进行处理,结果表明:液相计测数据中 80%以上误差位于±5%的范围以内,除个别小流量外,所有误差位于±10%的范围以内;气相计测结果中 90%以上误差位于±10%的范围以内, 97%的误差位于±15%的范围以内。实验数据表明:该计测模型可以适用于多相流中不同粘度的液相流量计量;可适用于较宽的气、液相流量变化范围,模型计测误差稳定在可接受的水平。     

Microvisual Study of Multiphase Gas Condensate Flow in Porous Media

Gas condensate reservoirs constitute a significant portion of hydrocarbon reserves worldwide. The liquid drop-out in these reservoirs may lead to recovery problems such as near wellbore permeability impairment and uncertainty in the actual location of the target condensate. Such technical issues can be addressed through improved understanding of the formation of condensate and the multiphase flow of gas/condensate/water in the reservoir as characterized by relative permeability curves. The appropriate relative permeability curves in turn can be used in reservoir simulators to assist in optimization of field development. This paper reports results of experiments conducted in micromodels, in support of possible core flow tests, using reservoir fluids under reservoir conditions. In particular, visualizations of condensate formation with and without connate water are presented and the differences between the two cases as well as the possible implications for the relative permeability measurements are discussed. Furthermore, the flow of gas and condensate at different force ratios (capillary and Bond numbers) are presented. It is postulated that a single dimensionless number may not be sufficient to characterize the multiphase flow in gas condensate reservoirs. The physical mechanisms occurring under various field conditions are examined in the light of these observations.     

Micro-continuum Framework for Pore-Scale Multiphase Fluid Transport in Shale Formations

Transport in Porous Media - A micro-continuum simulation framework is proposed to study the complex pore-scale dynamics associated with hydrocarbon recovery from shale gas. The model accounts for...     

Influence of Numerical Cementation on Multiphase Displacement in Rough Fractures

We present an application of 3D X-ray computed microtomography for studying the influence of numerical cementation on flow in a cement-lined rough-walled fracture. The imaged fracture geometry serves as input for flow modeling using a combination of the level set and the lattice Boltzmann methods to characterize the capillary-dominated fluid displacement properties and the relative permeability of the naturally cemented fracture. We further numerically add cement to the naturally cement-lined fracture to quantify the effect of increasing cement thickness and diminishing aperture on flow properties. Pore space geometric tortuosity and capillary pressure as a function of water saturation both increase with the numerically increased fracture cement thickness. The creation of unevenly distributed apertures and cement contact points during numerical cement growth causes the wetting and non-wetting fluids to impede each other, with no consistent trends in relative permeability with increasing saturation. Tortuosity of wetting and non-wetting fluid phases exhibits none to poor correlation with relative permeability and thus cannot be used to predict it, contrary to previous findings in smoother fractures.     

多相材料微结构多目标拓扑优化设计

在采用多尺度均匀化方法求解微结构等效特性的基础上，提出了多相材料 微结构的多目标优化设计模型. 以组分材料用量为约束，采用周长控制消除棋盘格，结合有 限元方法和对偶凸规划求解技术，对两相和三相材料微结构多项等效模量的组合进行了优化 设计. 研究比较了微结构网格粗细、材料组分以及三相材料微结构优化中的两相实体材料弹 性模量相对比例不同对优化结果的影响. 数值算例验证了优化模型和优化算法的有效性，表 明了相关因素对优化结果的影响.     

Predictive Pore-Scale Modeling of Single and Multiphase Flow

We show how to predict flow properties for a variety of rocks using pore-scale modeling with geologically realistic networks. The pore space is represented by a topologically disordered lattice of pores connected by throats that have angular cross-sections. We successfully predict single-phase non-Newtonian rheology, and two and three-phase relative permeability for water-wet media. The pore size distribution of the network can be tuned to match capillary pressure data when a network representation of the system of interest is unavailable. The aim of this work is not simply to match experiments, but to use easily acquired data to estimate difficult to measure properties and to predict trends in data for different rock types or displacement sequences.     

Multiphase drag reduction: Effect of eliminating slugs

Two-phase pressure drop measurements were taken for air/water mixtures in a 0.052-m diameter horizontal pipe with special focus on the superficial liquid velocity range of 0.03–1.2 m/s at superficial gas velocities of 3.8, 5.2, and 6.6 m/s. It was found that the addition of 400 ppm of sodium dodecyl sulfate (SDS) to the water reduced the pressure drop by 25–40% when compared to equal flow rates without SDS. The pressure drop reduction occurred where the SDS eliminated the occurrence of the intermittent flow present with water. It was also found that the same concentration of SDS had virtually no effect on single phase liquid pressure drop. The pressure drop reduction appears to be due solely to the suppression of intermittent flow patterns.     

第四届国际多相流会议简介

１会议概况第四届国际多相流会议于２００１年５月２７日到６月１日在美国Ｎｅｗ　Ｏｒｌｅａｎｓ召开．本次会议约有８００多名来自美国,加拿大,欧洲,亚洲（包括中,日,韩,　印等国）的代表参加,宣读论文共５６５篇,其中邀请报告２０篇,分组口头报告和张贴论文５４５篇．中国有清华大学周力行,杨瑞昌,西安交大陈学俊,林宗虎,陈听宽等,中科院工程热物理所蔡瑞贤,浙江大学林建忠,华中科技大学柳朝晖和大庆石油学院的２位代表共１１人参加,宣读论文１０余篇,其中周力行应邀做邀请报告１篇,宣读分组口头报告２篇,张贴论文１…