A novel inorganic/organic composite membrane tailored by various organic silane coupling agents for use in direct methanol fuel cells

A series of organic silica/Nafion composite membranes has been prepared by using organic silane coupling agents (SCA) bearing different hydrophilic functional groups. The physico-chemical properties of the composite membranes have been characterized by electrochemical techniques, scanning electron microscopy (SEM), diffuse-reflection Fourier-transform infrared spectroscopy (DRFTIR), wide-angle X-ray diffraction (WAXRD), thermogravimetric analysis (TGA), and thermogravimetric mass spectrometry (TG-MS). It has been found that some organic silica/Nafion composite membranes modified by organic silane agents bearing amino groups exhibit extremely low methanol crossover and proton conductivity values, e.g., a composite membrane shows a proton conductivity that is about five orders of magnitude lower and a methanol permeability that is about three orders of magnitude lower than those of a Nafion117 membrane. However, under optimized conditions for controlling the basicity of the amino groups, we also obtained a composite membrane with 89% lower methanol permeability and 49% lower proton conductivity compared with Nafion117 membrane. The results clearly demonstrate that the diffusion of methanol and protons through the membrane can be controlled by adjusting the functional groups on the organic silica.     

Research on two‐phase flow considering hydrogen crossover in the membrane for a polymer electrolyte membrane fuel cell

Hydrogen crossover has an important effect on the performance and durability of the polymer electrolyte membrane fuel cell (PEMFC). Severe hydrogen crossover can accelerate the degradation of membrane and thus increase the possibility of explosion. In this study, a two‐phase, two‐dimensional, and multiphysics field coupling model considering hydrogen crossover in the membrane for PEMFC is developed. The model describes the distributions of reactant gases, current density, water content in membrane, and liquid water saturation in cathode electrodes of PEMFC with intrinsic hydrogen permeability, which is usually neglected in most PEMFC models. The conversion processes of water between gas phase, liquid phase, and dissolved water in PEMFC are simulated. The effects of changes in hydrogen permeability on PEMFC output performance and distributions of reactant gases and water saturation are analyzed. Results showed that hydrogen permeability has a marked effect on PEMFC operating under low current density conditions, especially on the open circuit voltage (OCV) with the increase of hydrogen permeability. On the contrary, the effect of hydrogen permeability on PEMFC at high current density is negligible within the variation range of hydrogen permeability in this study. The nonlinear relations of OCV with hydrogen diffusion rate are regressed.     

地下水源热泵运行时渗透系数对含水层的影响

为减少地下水源热泵运行对地下空间的影响,运用颗粒迁移理论研究了地下水源热泵长期运行时渗透系数对含水层参数变化特性的影响。结果表明,随着地下水源热泵的长期运行,含水层孔隙率和渗透系数的变化特性与渗透系数的初始值无关,而承压水头的变化特性则受渗透系数的影响,渗透速度为影响含水层参数变化的重要因素之一,较小的渗透速度可有效减少地下水源热泵运行对地下空间的影响。     

偏态分布模型在碾压混凝土坝体渗流分析中的应用

在渗透稳定的可靠性分析中,确定渗透系数的概率分布非常必要。基于渗透系数概率分布构建了偏态分布模型,结合江垭碾压混凝土坝体的透水率试验数据及渗透系数和透水率的换算因子对渗透系数进行了随机性分析,并编制相应的FORTRAN程序,采用偏态分布概率密度函数拟合渗透系数的概率分布。结果表明,利用FORTRAN程序对渗透系数进行偏态分布拟合,能获得较理想的概率密度曲线;采用众数和综合标准差代替均值和均方差作为统计值,可使结果更合理、可靠。     

The dependence of permeability on effective stress from flow tests at hot dry rock reservoirs at Rosemanowes (Cornwall) and Fenton Hill (New Mexico)

Effective stress is the primary control on permeability and thus on flow and water loss for two-well hot dry rock systems involving injection and production that have been tested to date. Theoretical relations are derived for the flow between an injector and producer, including the dependence of permeability on effective stress. Four relations for permeability as a function of effective stress are used to match field data for the hot dry rock systems at Rosemanowes, Cornwall, and Fenton Hill, New Mexico. The flow and water loss behavior of these systems are well explained by the influence of effective stress on permeability. All four relations for permeability as a function of effective stress are successful in matching the field data, but some have difficulty in determining unique values for elastic and hydrologic parameters.     

Analytical determination of viscous permeability of fibrous porous media

In this study, the permeability of ordered fibrous media towards normal and parallel flow is determined analytically. In this approach, porous material is represented by a “unit cell” which is assumed to be repeated throughout the media. Several fiber arrangements including: touching and non-touching arrays are considered. Modeling 1D touching fibers as a combination of channel-like conduits, a compact relationship is proposed to predict permeability. Furthermore, employing an “integral technique” and assuming a parabolic velocity profile within the unit cells, analytical relationships are developed for pressure drop and permeability of rectangular arrangements. The developed models are successfully verified with existing experimental data collected by others for square arrangement over a wide range of porosity. Due to the random nature of the porous micro structures, determination of exact permeability of real fibrous media is impossible. However, the analyses developed for ordered unit cells enable one to predict the trends observed in experimental data. The effects of unit cell aspect ratio and fibers diameter on the permeability are also investigated. It is noted that with an increase in the aspect ratio the normal permeability decreases while, the parallel permeability remains constant. It is also shown that the permeability of fibrous media is related to the diameter of fibers squared.     

贵州合层开发煤层气井产层孔渗特征研究

贵州省煤层发育,煤层气资源富集,对其合层开发煤层气产层孔渗特征进行研究能够为煤层气高产、稳产提供依据。基于贵州合层排采煤层气井产层特征统计,综合现有地质及工程数据,系统研究产层孔渗特征。研究结果表明：贵州境内受煤变质程度高的影响,煤层气产层孔隙度较低,主要在2% ～ 6%之间;煤储层大多发育两组相互近正交的内生裂隙,外生裂隙则与区内深大断裂活动以及煤层厚度有关;产层渗透率均低于0.35 mD,属于中低渗透率产层,且以小于0.1 mD的低渗产层为主。     

Capillary Performance of Micropillar Arrays in Different Arrangements

In this study, permeability and capillary pressure of copper micropillar structures (height: 50 µm, diameter: 50 µm) in different arrangements (hexagonal, rectangular, and square) and different porosities (0.45/0.5, 0.6, 0.7, 0.8) are compared experimentally and numerically. The micropillar structures are fabricated on copper clad printed circuit board with electroplating, and the samples are coated with silica nanoparticles to enhance wettability. A forced liquid flow test is used to measure permeability of the samples, and capillary rate-of-rise measurement technique is used to determine the capillary pressure of the wicks. In the permeability model, the effect of meniscus curvature is considered, and the results are compared with other permeability models. Capillary pressure is predicted by using surface energy minimization tool, Surface Evolver. The test results show that the micropost array in rectangular arrangement have the highest permeability, and similar capillary pressure compared to other pillar arrangements with the same porosity, and thus show the highest capillary performance parameter. The effect of gravity on the sample characterization with capillary rate-of-rise test is also studied to investigate the feasibility of applying Washburn’s equation to test data.     

Impact of experimentally measured relative permeability hysteresis on reservoir-scale performance of underground hydrogen storage (UHS)

Underground Hydrogen Storage (UHS) is an emerging large-scale energy storage technology. Researchers are investigating its feasibility and performance, including its injectivity, productivity, and storage capacity through numerical simulations. However, several ad-hoc relative permeability and capillary pressure functions have been used in the literature, with no direct link to the underlying physics of the hydrogen storage and production process. Recent relative permeability measurements for the hydrogen-brine system show very low hydrogen relative permeability and strong liquid phase hysteresis, very different to what has been observed for other fluid systems for the same rock type. This raises the concern as to what extend the existing studies in the literature are able to reliably quantify the feasibility of the potential storage projects. In this study, we investigate how experimentally measured hydrogen-brine relative permeability hysteresis affects the performance of UHS projects through numerical reservoir simulations. Relative permeability data measured during a hydrogen-water core-flooding experiment within ADMIRE project is used to design a relative permeability hysteresis model. Next, numerical simulation for a UHS project in a generic braided-fluvial water-gas reservoir is performed using this hysteresis model. A performance assessment is carried out for several UHS scenarios with different drainage relative permeability curves, hysteresis model coefficients, and injection/production rates. Our results show that both gas and liquid relative permeability hysteresis play an important role in UHS irrespective of injection/production rate. Ignoring gas hysteresis may cause up to 338% of uncertainty on cumulative hydrogen production, as it has negative effects on injectivity and productivity due to the resulting limited variation range of gas saturation and pressure during cyclic operations. In contrast, hysteresis in the liquid phase relative permeability resolves this issue to some extent by improving the displacement of the liquid phase. Finally, implementing relative permeability curves from other fluid systems during UHS performance assessment will cause uncertainty in terms of gas saturation and up to 141% underestimation on cumulative hydrogen production. These observations illustrate the importance of using relative permeability curves characteristic of hydrogen-brine system for assessing the UHS performances.     

Lattice Boltzmann simulations of anisotropic permeabilities in carbon paper gas diffusion layers

The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) with multi-reflection solid boundary conditions is used to study anisotropic permeabilities of a carbon paper gas diffusion layer (GDL) in a fuel cell. The carbon paper is reconstructed using the stochastic method, in which various porosities and microstructures are achieved to simulate different samples. The simulated permeability and tortuosity show anisotropic characteristics of the reconstructed carbon papers with in-plane permeability higher than through-plane, and in-plane tortuosity lower than through-plane. The calculated permeabilities are in good agreement with existing measurements. The relationship between the permeability and the porosity is fitted with empirical relations and some fitting constants are determined. Furthermore, the obtained relationship of tortuosity and porosity is used in a fractal model for permeabilities. The results indicate that the fractal model and the Kozeny–Carman equation provide similar predictions on the through-plane permeability of the carbon paper GDL.     

Numerical study on permeability of gas diffusion layer with porosity gradient using lattice Boltzmann method

In this paper, the lattice Boltzmann method (LBM) has been employed to explore the permeability and internal fluid flow behavior of the gas diffusion layer (GDL). Three different non-uniform porosity distributions are designed as linear type, stepped type, and transitional type and compared with constant porosity samples. Results show that the linear porosity gradient distribution leads to higher permeability values compared with the other two types. For samples with total porosity of 0.65 and 0.75, optimal porosity gradient distributions bring about an enhancement of permeability have been found. The impact of porosity gradient distribution on the velocity field is presented. Dependencies of permeability with porosity and tortuosity are demonstrated through several fitted equations.     

A fractal permeability model for bi-dispersed porous media

In this paper a fractal permeability model for bi-dispersed porous media is developed based on the fractal characteristics of pores in the media. The fractal permeability model is found to be a function of the tortuosity fractal dimension, pore area fractal dimension, sizes of particles and clusters, micro-porosity inside clusters, and the effective porosity of a medium. An analytical expression for the pore area fractal dimension is presented by approximating the unit cell by the Sierpinski-type gasket. The pore area fractal dimension and the tortuosity fractal dimension of the porous samples are determined by the box counting method. This fractal model for permeability does not contain any empirical constants. To verify the validity of the model, the predicted permeability data based on the present fractal model are compared with those of measurements. A good agreement between the fractal model prediction of permeability and experimental data is found. This verifies the validity of the present fractal permeability model for bi-dispersed porous media.     

Gas slippage effect on the permeability of circular cylinders in a square array

The gas slippage phenomenon is usually observed when gas flow through porous media under low pressure, and has received an increasing attention for its importance in science and engineering. In the past decades, although many theoretical, numerical and experimental works have been done to predict the permeability of a square array of circular cylinders, little literature is available in studying the slippage effect on permeability. In this paper, the gas slippage effect on the permeability of circular cylinders in a square array is studied theoretically. The permeabilities at low and high solid fractions are derived with cell model and lubrication theory by coupling with a first-order slip boundary condition. The present results are finally validated through a comparison with some available results.     

应力和侵蚀性溶液渗透耦合作用下碳酸盐岩渗透特性试验研究

为研究不同应力及溶液组合下碳酸盐岩渗流特性演化规律,选择H2SO4溶液、蒸馏水作为渗透流体,使用岩石耦合渗透试验装置对碳酸盐岩试样分别进行较长时间的渗透试验,得到三种不同工况下岩石试样渗透率和渗出液中矿物离子浓度随时间变化的曲线,分析了试验中围岩、渗透压、溶液等影响因素与渗透率、岩石内部矿物质溶解规律之间的内在联系。结果表明,试验初期阶段,围压对岩样渗透率有较大影响,恒定围压施加后使得岩样孔隙受到压缩从而影响渗透率。试验过程中,渗透压的增大会导致岩样渗透率产生短时间的上升,随后岩样渗透率逐渐回落。不同渗透溶液则有不同的影响,H2SO4溶液对岩样内部的侵蚀性较强,在岩样上游段产生较强溶解,当溶解的矿物离子浓度达到过饱和后,可能在下游段产生沉淀,使得岩样整体渗透率不断降低;而蒸馏水对岩样的侵蚀作用较弱,沿程产生均匀溶解,不能对孔隙结构造成较大改变,整体渗透率保持稳定。岩样整体渗透率的变化是应力、渗透溶液的溶蚀作用和矿物沉淀共同作用的结果。研究成果可用于指导工程实践。     

含水合物沉积物的渗透率实验研究

天然气水合物储层的渗透率是影响水合物开采时气、水运移的关键,也是水合物开采潜力评价、资源评价、开采工艺选择等需要了解的关键参数.目前,国内外学者对天然气水合物储层的渗透率进行了一定的研究并有了初步认识.但是,对于围压、轴向压力、水合物饱和度、赋存模式等对水合物沉积物渗透率的影响机制和机理还不清楚.本文在自主设计的水合物...     

泵抽式电缆地层测试复合流形模型研究及应用

泵抽式电缆地层测试是在油气资源评价中快速获得储层的渗透率的技术手段。目前对泵抽式电缆地层测试压力资料分析多采用球形流分析法,而对于大排量泵抽式电缆地层测试器,在薄储层和储层的上下边界,测试流动形态则会从球形流过渡为柱形流,如果仍然采用球形流动解释方法,就会给解释结果带来较大的误差。通过分析泵抽式电缆地层测试储层流动形态,并应用油气层渗流力学理论,推导出了在球形流与柱形流复合流动形态下的渗透率求解模型。选择某油田一口井的电缆地层测试资料为例对该模型进行验证。由于测试目的层为层薄,渗流为球形流与柱形流复合流动形态,采用模型计算得到储层渗透率为46.6×10-3μm2,与该层段取心分析岩心渗透率(56×10-3μm2)接近,证明该渗透率求解模型可行。     

Effect of weave tightness and structure on the in-plane and through-plane air permeability of woven carbon fibers for gas diffusion layers

In this study, woven gas diffusion layers (GDLs) with varying weave type and tightness are investigated. Plain and twill weave patterns were manufactured in-house. The in-plane and through-plane air permeability of the woven samples were tested, and mercury intrusion porosimetry (MIP) tests were performed to study the pore structure. It was found that the twill weave has a higher permeability than the plain weave, which is consistent with literature. Like non-woven carbon papers, woven GDLs have higher in-plane permeability than through-plane permeability; however it has been shown that it is possible to manufacture a GDL with higher through-plane permeability than in-plane permeability. It was also concluded that the percentage of macropores in the weave is the driving factor in determining the through-plane air permeability. This work lays the groundwork for future studies to attempt to characterize the relationship between the weave structure and the air permeability in woven GDLs.     

杏南开发区含钙特低渗透储层井网层系优化数值模拟研究

杏南开发区储层包括含钙特低渗透储层、表外储层和表内储层.其沉积环境复杂,油层之间的岩石物性相差较大,开发后动用状况复杂,剩余油分布高度零散,调整挖潜难度大.依据杏南开发区含钙特低渗透储层发育特征和注水开发动态特点,结合目前区块剩余油分布,研究层系组合和加密调整对开发效果的影响,为进行注采系统调整提供依据.针对杏南开发区的特点,首先设计了层系与井网井距相结合的部署方案,层系设计包括:射开含钙特低渗透储层和表外储层;射开含钙特低渗透储层、表外储层和有效厚度小于0.5m的表内层;射开含钙特低渗透储层和所有油层.将3套层系与4种井网、井距情况相结合,组合为12套方案,进行开发指标预测方案优选.结合经济评价认为,方案3为最优方案,即在原井网排间分流线位置布采油井,原井网采油井全部转注,新老井共同组成注采井距150m线状注水井网,射开含钙特低掺透储层和所有油层.     

基于SWMM模型的渗渠LID措施补偿机理研究

针对低影响开发(LID)措施可有效削减洪峰流量和污染负荷,对降低洪涝灾害风险、保护生态环境具有重要作用,但其补偿机理尚不明确的问题,基于SWMM模型,采用控制变量法分别计算了不同大小的渗渠LID措施和相应透水率。结果表明,渗渠LID措施的补偿效果随渗渠LID措施的增大而增大,且渗渠LID措施大小与透水率之间存在定量补偿关系,可确定其补偿效果,为渗渠LID的布设提供了依据,也为LID措施的进一步发展提供了一种新思路。     

Application of lattice Boltzmann method to a micro-scale flow simulation in the porous electrode of a PEM fuel cell

The electrode of a PEM fuel cell is a porous medium generally made of carbon cloth or paper. Such a porous electrode has been widely modeled as a homogeneous porous medium with a constant permeability in the literature of PEM fuel cell. In fact, most of gas diffusion media are not homogeneous having non-isotropic permeability. In case of carbon cloth, the porous structure consists of carbon fiber tows, the bundles of carbon fiber, and void spaces among tows. The combinational effect of the void space and tow permeability results in the effective permeability of the porous electrode. In this work, the lattice Boltzmann method is applied to the simulation of the flow in the electrode of a PEM fuel cell. The electrode is modeled as void space and porous region which has certain permeability and the Stokes and Brinkman equations are solved in the flow field using the lattice Boltzmann model. The effective permeability of the porous medium is calculated and compared to an analytical calculation showing a good agreement. It has been shown that the permeability of porous medium is strongly dependant on the fiber tow orientation in three-dimensional simulations. The lattice Boltzmann method is an efficient and effective numerical scheme to analyze the flow in a complicated geometry such as the porous medium.