Hydrodynamic Characterization of Nickel Metal Foam,Part 1: Single-Phase Permeability

This article presents results of the investigation of the fluid dynamic behavior in CVD processed nickel metal foams. An experimental facility was developed to measure the single-phase permeability in nickel metal foams in Darcian flow regime. Data on permeability values of seven different nickel foam samples was obtained. The pore sizes of the foam were obtained with scanning electron microscope. By defining friction factor and Reynolds number based on the permeability length scale a correlation was obtained for the foam permeability in Darcian flow regime. The result from this study was compared with the correlations reported by other researchers, and was found to be in good agreement.     

A Theoretical Model with Experimental Verification to Predict Hydrodynamics of Foams

An experimentally validated theoretical model, based on hydraulic resistance network and scale analysis at the pore level, is developed to predict the pressure drop for flow through foams. The complex microstructure of the foams is modeled as a matrix of interconnected solid ligaments forming simple cubic arrays of cylinders. New correlations for permeability and form drag (inertia) coefficient are presented as functions of the mean pore and ligament diameter as well as the foam porosity. The present model makes it possible to conduct parametric studies. Results obtained from the proposed model are successfully compared with our experimental data as well those found in the literature to observe good agreement.     

Porosity–Permeability Relations for Evolving Pore Space: A Review with a Focus on (Bio-)geochemically Altered Porous Media

Reactive transport processes in a porous medium will often both cause changes to the pore structure, via precipitation and dissolution of biomass or minerals, and be affected by these changes, via changes to the material’s porosity and permeability. An understanding of the pore structure morphology and the changes to flow parameters during these processes is critical when modeling reactive transport. Commonly applied porosity–permeability relations in simulation models on the REV scale use a power-law relation, often with slight modifications, to describe such features; they are often used for modeling the effects of mineral precipitation and/or dissolution on permeability. To predict the reduction in permeability due to biomass growth, many different and often rather complex relations have been developed and published by a variety of authors. Some authors use exponential or simplified Kozeny–Carman relations. However, many of these relations do not lead to fundamentally different predictions of permeability alteration when compared to a simple power-law relation with a suitable exponent. Exceptions to this general trend are only few of the porosity–permeability relations developed for biomass clogging; these consider a residual permeability even when the pore space is completely filled with biomass. Other exceptions are relations that consider a critical porosity at which the porous medium becomes impermeable; this is often used when modeling the effect of mineral precipitation. This review first defines the scale on which porosity–permeability relations are typically used and aims at explaining why these relations are not unique. It shows the variety of existing approaches and concludes with their essential features.     

The Effect of Pore Structure on the Electrical Conductivity of Ti

Open-pore Ti foam samples with porosity in the range of 10–70% and average pore size of 150–400 μm was fabricated by powder metallurgy method using polymethyl methacrylate (PMMA) as space holder initially. The resulting foam is anisotropic: the pores are spheroidal, being shorter along the pressing direction than in the pressing plane. The pore anisotropy decreases as the size of the polymethyl methacrylate (PMMA) particles used increases and hence with pore size, which leads to a higher conductivity in the plane of the pressing. As the porosity increases, the conductivity of porous Ti decreases dramatically. The porosity e{\varepsilon} dependence of the electrical conductivity σ could be well described by Maxwell approximation, while the differential effective medium approximation is only suitable to porous Ti with finite size of 400 μm in the porosity range of 40–70%, i.e., high porosity metal with randomly oriented spheroids.     

镓铟锡液滴撞击泡沫金属表面的运动学特性研究

常温下为液态的镓铟锡合金以其优异的导热性能在具有特殊要求的传热领域有着重要的应用价值,与传统流动介质相比较大的表面张力使得其产生的流动现象必有所区别.本文研究镓铟锡所形成的液滴撞击泡沫金属表面后所产生的铺展、回缩及回弹现象.采用高速相机拍摄液滴投影轮廓随液滴运动的变化过程,并通过图像处理获得不同撞击速度、底板表面孔径下的液滴铺展系数、中心位置轮廓高度以及液滴回弹后在空中的振动特性.研究结果表明:具有较高表面张力的镓铟锡液滴的铺展系数随无量纲时间的变化在铺展初始阶段仍满足常规流体的1/2次幂关系,只在铺展后期与底板的无量纲孔径有关系;液滴的最大铺展系数在较小无量纲孔径底板大于在光滑镍板,且随底板无量纲孔径增大而逐渐减小;在回弹过程,由于底板孔隙结构的存在使得液滴回弹后在空中的振动呈现3种形态:规则的横向和纵向振动、带旋转的横向和纵向振动以及旋转振动;最后,通过对振动频率的拟合和分析,进一步拓展了传统振动频率理论公式在非规则振动过程预测中的应用.      

超临界CO_2作用后煤微观结构与渗透率变化规律实验研究

在宏观超临界CO_2增透实验基础上进行微观成像实验,提取煤微观孔隙特征,自编Matlab程序,计算孔隙率,得到煤各微区孔隙率和渗透率矩阵,绘制孔隙率和渗透率等值线图。结果表明:增透实验前后煤微观结构差别显著,经超临界CO_2作用后,煤微观孔隙充分发育,孔隙的数量、尺寸明显增加,孔隙率是增透前的9.11倍;随着孔隙压力的增大,煤中粒间孔隙数量增多,孔隙之间的连通性增加,孔隙率呈指数增大的趋势,煤体各微区孔隙率等值线密集程度增加;煤体的渗透率随着孔隙率的增加呈正指数递增的趋势,且随着孔隙压力的增加,渗透率呈指数递增的变化规律,渗透率等值线的密集程度增加,宏微观实验结果是一致的,随着注入超临界CO_2孔隙压力的增加,煤微观孔隙结构的发育程度提高,为煤层气的运移提供更多的通道,有效提高了煤体的渗透性。     

Effect of Confining Wall on Properties of Gas Flow Through Metal Foam: An Experimental Study

While the Darcy and Forchheimer relations are widely applied to determine the permeability and the form drag coefficient of open-cell metal foam, they both assume that the porous medium is infinite in all directions, i.e., large enough so that the effect of any confining walls is negligible. Many researchers, however, pay little or no attention to the size of metal foam samples in pressure-drop studies. The size of a foam sample perpendicular to the flow direction may be small enough such that wall effects are significant. This article experimentally investigates the wall effect on the permeability and form drag coefficient for two types of open-cell aluminum foam subjected to airflow entering the foam in the Forchheimer regime. The Forchheimer equation was recast in two different manners, which resulted in new non-dimensional numbers that correlated very well with the diameter of the foam samples measured in cells. The correlations are valid for a confining-tube-diameter-based Reynolds number ranging from approximately 13,000 to 105,000, and for diameters ranging from 12 to 36 cells and 24 to 60 cells for 10- and 20-pore per inch foam, respectively. The obtained correlations allow for determining pressure drop given only the velocity and the diameter of an aluminum foam sample.     

泡沫镍/环氧树脂/碳化硅双连续复合材料的料浆冲蚀行为研究

设计并制备出一种颗粒增强型双连续三元复合材料--泡沫镍/环氧树脂/碳化硅双连续复合材料,以材料的总损失量为重点研究了其在含氯化钠料浆冲蚀条件下的损伤行为.结果表明:颗粒增强的泡沫镍/环氧树脂/碳化硅双连续三元复合材料的耐料浆冲蚀性能明显优于环氧树脂/碳化硅二元复合材料;不同孔径泡沫镍骨架的复合材料的冲蚀量随攻角变化出现了不同的峰值;合理匹配泡沫镍骨架的孔径和体密度,可制备出具有优异抗冲蚀性能的颗粒增强双连续复合材料.     

Pressure drop and friction factor of steady and oscillating flows in open-cell porous media

Open-cell metal foams are often used in heat exchangers and absorption equipment because they exhibit large specific surface area and present tortuous coolant flow paths. However, published research works on the characteristics of fluid flow in metal foams are relatively scarce, especially for the flow oscillation condition. The present experimental investigation attempts to uncover the behavior of steady and oscillating flows through metal foams with a tetrakaidecahedron structure. In the experiments, steady flow was supplied by an auto-balance compressor and flow oscillation was provided by an oscillating flow generator. The pressure drop and velocity were measured by the differential pressure transducer and hot-wire sensor, respectively. The friction factor of steady flow in metal foam channel was analyzed through the permeability and inertia coefficient of the porous medium. The results show that flow resistance in the metal foams increases with increasing form coefficient and decreasing permeability. The empirical equation obtained by the present study indicates that the maximum friction factor of oscillating flow through the tested aluminum foams with specific structure is governed by the hydraulic ligament diameter-based kinetic Reynolds number and the dimensionless flow amplitude.     

不同孔隙率及孔径泡沫铝的力学与吸能特性研究

对三种孔径两种孔隙率共六种泡沫铝试件进行了静态压缩试验,发现对于中孔隙率材料,孔隙率对材料力学性能和吸能性能仍有明显影响:孔隙率越大,其吸能能力越强,但是屈服极限越小.孔径对材料吸能能力也有一定影响.同时,试验中还发现,对于孔隙率为55%的材料,当孔径≤1mm时,泡沫铝材料的孔径对其力学性能及吸能性能影响甚小.     

Correlations for the pressure drop for flow through metal foam

Steady-state unidirectional pressure-drop measurements for incompressible airflow through nine open-cell aluminum foam samples, having different porosities and pore densities, were undertaken. The pressure drop increased with increasing Darcian velocity following the quadratic Forchheimer equation. The lower-porosity foam produced significantly higher pressure drop. Both the permeability and the form drag coefficient correlated well with the porosity. The correlations predicted the results of some previous studies reasonably well, especially for the low-pore-density foam.     

Experimental study of air natural convection on metallic foam-sintered plate

The natural convection on metallic foam-sintered plate at different inclination angles was experimentally studied. Seven copper foam samples with different pore densities (10–40 pore per inch), porosities (0.90–0.95), and aspect ratios (the ratio of foam thickness to sample length, 0.1–0.5) were measured at inclination angles of 0° (vertical orientation), 15°, 30°, 45°, 60°, 75°, 90° (horizontal orientation). The heat conduction and natural convection inside the foam both contributed to the total heat transfer. Although, the form and viscous drag, which are influenced by permeability and viscous friction in the thermal boundary layer respectively, tend to suppress the natural convection, the heat transfer was finally enhanced by the foam sintered surface due to large surface area extension. Optimum inclination range 60–75° corresponding to maximum average Nu number was found in the heat flux range of 600–1800 W/m². The sintered foam surface with lower porosity and pore density was recommended for heat transfer enhancement. Particularly, the sample with porosity 0.9, pore density of 10 PPI, aspect ratio of 0.5 offered the highest average Nu number among the studied samples. An empirical correlation for modified Nusselt number at isoflux boundary condition considering the foam morphology parameter and inclination angle was proposed within deviation ±15% between the correlation and the experimental data.     

Particle Flow Code Method-Based Meso-scale Identification for Seepage Failure of Soil Levee

The development and validation of a grid-based pore-scale numerical modelling methodology applied to five different commercial metal foam samples is described. The 3-D digital representation of the foam geometry was obtained by the use of X-ray microcomputer tomography scans, and macroscopic properties such as porosity, specific surface and pore size distribution are directly calculated from tomographic data. Pressure drop measurements were performed on all the samples under a wide range of flow velocities, with focus on the turbulent flow regime. Airflow pore-scale simulations were carried out solving the continuity and Navier–Stokes equations using a commercial finite volume code. The feasibility of using Reynolds-averaged Navier–Stokes models to account for the turbulence within the pore space was evaluated. Macroscopic transport quantities are calculated from the pore-scale simulations by averaging. Permeability and Forchheimer coefficient values are obtained from the pressure gradient data for both experiments and simulations and used for validation. Results have shown that viscous losses are practically negligible under the conditions investigated and pressure losses are dominated by inertial effects. Simulations performed on samples with varying thickness in the flow direction showed the pressure gradient to be affected by the sample thickness. However, as the thickness increased, the pressure gradient tended towards an asymptotic value.     

Permeability of Pore Networks Under Compaction

The characteristic pore length fixes the scale of permeability of a porous medium. For pore networks undergoing strong random compaction, this length becomes singular at transition porosities, revealing a change in the microstructure of the porespace controlling the transport. Nodal balances and lattice Boltzmann simulations of flow in pore networks under compaction show that the scaling between permeability and porosity changes near the transition porosities. Simulation results are compared with experimental permeability data from transparent two-dimensional micromodels of networks decorated with the same pore size distribution. Permeability?Cporosity data of media undergoing smooth compaction is well described by a single power law. Under strong compaction, however, the scaling between permeability and porosity is possible by traits only, the scaling exponent changes notably at given transition porosities. These behaviors are common to a wealth of permeability?Cporosity data thus far unexplained.     

Simulation of Entry-Region Flow in Open-Cell Metal Foam and Experimental Validation

Open-cell metal foam is distinguished from traditional porous media by its very high porosities (often greater than 90 %), and its web-like open structure and good permeability. As such, the foam is a very attractive core for many engineered systems, e.g., heat exchangers, filtration devices, catalysts, and reactors. The flow field inside the foam is rather complex due to flow reversal and vigorous mixing. This complexity is increased by the possible presence of an entry region. The entrance region in metal foam is usually underestimated and ignored, just like its counterpart in traditional porous media. In this paper, the actual entry length is determined by simulation and direct experiment on commercial open-cell aluminum foam. It is shown to be dependent on flow velocity and to reach a constant value for higher velocities. The complex and intrinsically random architecture of the foam is idealized using a unit geometrical model, in order to numerically investigate the flow field and pressure drop inside the foam. The Navier–Stokes equations are solved directly, and velocity and pressure fields are obtained for various approach velocities using a commercial numerical package. The entry length is ascertained from the behavior of the velocity field close to the entrance. Comparisons to experimental data were also carried out. The commercial foam that was used in the experiment had 10 ppi and porosity of 91.2 %. Air was forced to flow inside the foam using an open-loop wind tunnel. Good qualitative agreement between the modeling and experimental results are obtained. The agreement lends confidence to the modeling approach and the determined entry length.     

Correlation of Water Vapor Permeability with Microstructure Characteristics of Building Materials Using Robust Chemometrics

This paper studies various microstructure parameters of natural and artificial building materials and aims to their correlation to the water vapor permeability. Three categories of building materials were investigated: stones, bricks, and plasters. Mercury intrusion porosimetry was applied in order to obtain the materials microstructure characteristics, a variety of pore size distributions and pore structure measurements, such as total porosity. The water vapor permeability of materials was determined experimentally according to ASTM standard E96-00. A robust principal component regression approach, coupled with multiple outlier detection, was applied in order to correlate water vapor permeability values to pore size distributions. A good quality correlation model was found by utilizing relative specific pore volume and relative specific pore surface distributions, whereas using pore structure measurements, such as total porosity, the correlation results were very poor. From the results, specific ranges of pore size distribution, corresponding to pores radius sizes greater than $10\,\upmu \text{ m }$ 10 μ m and between 1.778 and $0.421\,\upmu \text{ m }$ 0.421 μ m , contribute to the water vapor permeability of the materials.     

周期性吸声多孔材料微结构优化设计

多孔材料的吸声性能与材料孔隙率以及材料微结构几何构型存在密切相关.本文采用有限元方法研究了材料微观结构与宏观声学性能参数之间的关系,分析了通孔材料微结构的开孔形状、孔隙率以及孔隙尺寸对材料吸声性能的影响,并建立了在特定频率下具有高声吸收性能的通孔材料微结构几何构型的设计理论和方法,得到了具有较高声能吸收率的多孔材料微结构构型.     

Petrophysical and Capillary Properties of Compacted Salt

This paper reports experimental results that demonstrate petrophysical and capillary characteristics of compacted salt. The measured data include porosity, gas permeability, pore size distribution, specific surface area, and gas-brine breakthrough and capillary pressure. Salt samples employed in the experiments were prepared by compacting sodium chloride granulates at high stresses for several hours. They represent an intermediate consolidation stage of crushed salt under in-situ conditions. The porosity and permeability of compacted salt showed similar trends to those expected in backfilled regions of waste repositories excavated in salt rock. The correlation between the measured porosity and permeability seems to be independent of the compaction parameters for the range examined in this study. The correlation also shows a different behaviour from that of rock salt. The data of all petrophysical properties show that the pore structure of compacted salt can be better characterized by fracture permeability models rather than capillary bundle ones. Simple creep tests, conducted on the fully-brine-saturated compacted salt samples, yielded similar strain rates to those obtained by a steady-state mechanical model developed from the tests on fully brine-saturated granular salt. A modified procedure is proposed for the evaluation of restored-state capillary pressure data influenced by the material creep. The characteristic parameters for the capillary behaviour of compacted salt are determined by matching the Brooks-Corey and van Genuchten models with the measured data. The Leverett functions determined with different methods agree well.     

Permeability of open-cell foams under compressive strain

A model for the behavior of low-density, open-cell foam under compressive strain is proposed. Using this model, a tractable relationship between the normalized permeability and the applied strain is developed. An experimental study of the effect of strain on the permeability of open-cell polyurethane foams is presented. The experiments are performed using a Newtonian fluid in the fully laminar regime, where viscous forces are assumed to dominate. The model is found to describe the experimental data well and be independent of the foam cell size, the direction of flow with respect to the foam rise direction, and the properties of the saturating fluid. In a companion paper, the model for the permeability of open-cell foam is combined with Darcy’s law to give the contribution of viscous fluid flow to the stress–strain response of a reticulated foam under dynamic loading.