孔隙随机结构对非均质多孔泡沫导热性能的影响

多孔泡沫是一类低密度、高比表面积、具有独特性能的新型功能材料。实际多孔泡沫材料通常是非均质的,即其孔隙结构分布是随机的。为研究非均质多孔泡沫材料的导热性能,提出用孔隙均匀度作为表征孔隙结构分布随机性的参数,以多孔石墨泡沫为例,分析孔隙均匀度对多孔泡沫有效热导率的影响。数值计算结果表明：孔隙结构分布越不均匀,多孔泡沫材料的导热性能越差。根据计算结果提出了非均质石墨泡沫相对有效热导率的预测式,并与现有文献报道的结果进行了比较,发现当前结果呈现了孔隙结构随机性对材料有效热导率的影响,与ORNL实验结果更吻合。     

孔隙随机结构对非均质多孔泡沫导热性能的影响

多孔泡沫是一类低密度、高比表面积、具有独特性能的新型功能材料。实际多孔泡沫材料通常是非均质的,即其孔隙结构分布是随机的。为研究非均质多孔泡沫材料的导热性能,提出用孔隙均匀度作为表征孔隙结构分布随机性的参数,以多孔石墨泡沫为例,分析孔隙均匀度对多孔泡沫有效热导率的影响。数值计算结果表明:孔隙结构分布越不均匀,多孔泡沫材料的导热性能越差。根据计算结果提出了非均质石墨泡沫相对有效热导率的预测式,并与现有文献报道的结果进行了比较,发现当前结果呈现了孔隙结构随机性对材料有效热导率的影响,与ORNL实验结果更吻合。     

岩石特性参数随孔隙压力变化的预测研究

地层岩石骨架、地层流体及孔隙压力系统组成一个统一整体,改变任何一方都将改变岩石特性参数。在地层条件下,孔隙压力系统易发生改变,研究孔隙压力与岩石特性参数之间的定量关系对准确预测坍塌、破裂压力,指导现场安全钻进具有重要意义。本文利用有效应力原理及有效应力与声波速度的正相关关系,确定孔隙压力与声波时差之间存在定量关系,结合伽马测井、密度测井等得到岩石特性参数随孔隙压力变化的计算模型。通过实例验证计算,结果表明:该方法得到的岩石特性参数变化规律与室内岩心实验获得规律完全一致——岩石粘聚力、单轴抗压强度、弹性模量及抗拉强度与孔隙压力正相关,内摩擦角及泊松比与孔隙压力负相关。该方法具有岩心实验无法比拟的优点:计算过程简单,无需岩心,获取岩石特性参数剖面成本低,能够进一步准确预测坍塌、破裂压力剖面。     

基于分形理论的高煤阶煤岩渗透率计算方法研究与应用

为了提供有效的煤岩渗透率计算斱法,基于分形理论推导了煤样渗透率计算模型,提出了相应参数的获取斱法,基于高压压汞实验获得的毛管压力数据和实验测得的相应煤样的渗透率数据验证了计算斱法的正确性,并基于该斱法利用数值模拟的斱法分析了煤样渗透率的主要影响因素。结果表明,分形理论的煤岩渗透率计算斱法能够有效预测煤岩渗透率,平均误差仅为6.84%;煤岩分形维数、迂曲度和最大孔隙半径对渗透率具有重要影响,煤岩渗透率随着分形维数和迂曲度增加而降低,随最大孔隙半径增加而增加。     

石墨泡沫材料性能研究的随机建模方法

石墨泡沫是一种新型多孔材料,具有内表面积大、低密度、高导热等优异热性能.基于泡沫类多孔材料内部孔隙空间位置及孔径分布的局部不均匀性质,提出了一种均匀随机几何模型的建模方法,用于石墨泡沫导热性能的数值模拟,并将容积导热系数的模拟结果与美国ORNL的实测数据作了比较.     

致密破碎多孔介质渗透率测量方法

基于均匀各向同性多孔介质、达西渗流和理想气体假设,考虑Klinkenberg效应建立了针对具有纳米尺度孔径的低渗透率多孔介质中的渗流模型。针对致密球形破碎样品的压力脉冲实验,建立了相应的边界条件,同时利用有限差分方法获得其实验腔的压力变化曲线的数值解。通过对渗流方程进行量纲1化,引入了与孔隙率、渗透率和滑移参数有关的量纲1参数Z、Z*和bK。通过改变参数Z、Z*和bK研究了样品边界处压力的变化规律,给出了一种数据处理方法,对于致密球形破碎多孔介质的压力脉冲实验,通过对实验测量的样品边界处压力曲线的分析,结合偏微分方程正问题的数值解,可以确定样品的孔隙率、渗透率和滑移参数,从而更为简便地分析压力脉冲衰减曲线实验数据,得到致密多孔介质样品渗透率。     

氮吸附法表征多孔材料的孔结构

采用低温氮吸附法表征了具有不同孔结构的碳纳米管、碳分子筛、活性炭、分子筛和石墨化炭黑等多孔材料的孔径分布。氮吸附一脱附等温线利用康塔公司NOVA3000在相对压力0．001-1范围内测定。五种材料的比表面积在100-1000m2／g之间。低压下的吸附等温线和高压下的脱附等温线分别用HK方法和BJH方法解析,结果表明:五种多孔材料既含有发达的微孔,又含有一定数量的中孔。孔径大小及其分布的细微信息在色谱采样中能够预测吸附剂的吸附性能,也是新型多孔材料开发的关键。     

CVD法制备多孔碳材料及其气体吸附性能研究

以乙炔为原料,沸石为模板剂,通过化学气相沉积(CVD)法制备了多孔碳材料,利用SEM图和N2吸附脱附研究了不同反应温度对实验样品孔隙结构的影响,并分析其孔隙结构对CO2的吸附性能的影响。实验结果表明:反应温度为700℃时多孔碳材料具有较大的比表面积和微孔孔容,而温度达到1000℃时,多孔碳材料具有较大的介孔孔容和平均孔径。ZC-700对于CO2吸附量呈现出最大值248 mg/g(25℃,1 bar),说明了微孔结构对CO2吸附性能起主导作用。     

基于REV的孔隙型多孔介质导热分析模型

多孔介质内部组成结构复杂，热质传递过程多变，如何针对多孔介质的微观孔隙分布特性，建立更加精准的分析模型，有待深入研究。基于表征单元体（representative elementary volume，REV）概念，提出了孔隙型多孔介质的两种微观物理模型，即空心骨架基元模型和实心颗粒基元模型，分别建立了相应的热导率计算公式。针对孔隙内的微观结构特征，采用分形方法，对两种基元模型进行了分形修正，更好地表征了微观孔隙结构。基于所建模型，进行了模拟计算，探讨了相关参数对多孔介质导热特性的影响。通过自主研发的实验装置进行了相关实验，验证了模型的准确性。     

致密破碎多孔介质渗透率测量方法

基于均匀各向同性多孔介质、达西渗流和理想气体假设,考虑Klinkenberg效应建立了针对具有纳米尺度孔径的低渗透率多孔介质中的渗流模型。针对致密球形破碎样品的压力脉冲实验,建立了相应的边界条件,同时利用有限差分方法获得其实验腔的压力变化曲线的数值解。通过对渗流方程进行量纲1化,引入了与孔隙率、渗透率和滑移参数有关的量纲1参数Z、Z^*和b_K。通过改变参数Z、Z^*和b_K研究了样品边界处压力的变化规律,给出了一种数据处理方法,对于致密球形破碎多孔介质的压力脉冲实验,通过对实验测量的样品边界处压力曲线的分析,结合偏微分方程正问题的数值解,可以确定样品的孔隙率、渗透率和滑移参数,从而更为简便地分析压力脉冲衰减曲线实验数据,得到致密多孔介质样品渗透率。     

Thermally bonded nonwoven filters composed of bicomponent polypropylene/polyester fiber. I. Statistical approach for minimizing the pore size

A statistical approach involving the uniform design of experiments and regression analysis is used to investigate the effects of thermal bonding process parameters, dwell time, thermal bonding temperature, and hot air velocity, on the pore size of three‐dimensional (3D) nonwoven filters. These filters are produced from polypropylene (PP)/polyester (PET) (sheath/core) bicomponent staple fibers. The pore structures of the filter samples were examined using the capillary flow porometer. Results reveal that the statistical approach is effective in identifying the effects of the investigated process parameters on both the bubble point pore diameter and the mean flow pore diameter for the thermally bonded nonwoven filter samples. Under the optimized processing parameters for achieving the minimized pore size, the predicted minimum bubble point pore diameter is 111.12 μm and the predicted minimum mean flow pore diameter is 63.4 μm for the filter sample with the area density of 60 g/m². They are in good agreement with the experimental values of 111.71 and 60.91 μm, respectively. Microstructure features observed using scanning electron microscope indicate that the effects of the investigated process parameters on the pore size are closely related to the thermal energy delivered to the fibers and the pressure drop acting on the fabrics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2689–2699, 2006     

Effect of confinement on the bubble points of hydrocarbons in nanoporous media

The bubble point of reservoir petroleum fluids in nanoporous media is an important parameter in shale oil production. We present experimental results on the bubble points of octane and decane confined in controlled‐pore glasses (CPGs) with pore sizes of 4.3 and 38.1 nm. Differential scanning calorimetry (DSC) is used to measure the temperature at which the vapor phase begins to form (i.e., the bubble point). We find that the bubble point is dramatically affected by pore diameter: at 38.1 nm the confinement effect is insignificant, but at 4.3 nm two distinct bubble points appear, suggesting two distinct populations of evaporating fluid. Deviations are as great as ±15 K for both peaks relative to the bulk bubble point for 4.3 nm CPGs. Thermogravimetric analysis is consistent with DSC, supporting the validity of these results. Based on these experiments and previous simulations, we propose a two‐state model for the nanoconfined hydrocarbons. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1772–1780, 2016     

多孔介质中流动泡沫的压力分布计算

将多孔介质简化为一簇变截面毛细管组成的毛细管束,根据多孔介质的颗粒直径、颗粒排列方式、孔喉尺度比以及束缚水饱和度,计算出变截面毛细管的喉道半径和孔隙半径。在考虑多孔介质喉道和孔隙中单个气泡的受力和变形基础上,利用质量守恒定理和动量守恒定理,推导出单个孔隙单元内液相的压力分布和孔隙单元两端的压力差计算公式,最终得到多孔介质的压力分布以及多孔介质中泡沫当量直径计算方法。利用长U型填砂管对多孔介质中稳定泡沫的流动特性进行了实验研究,并对实验结果和计算结果进行了对比。结果表明:稳定泡沫流动时多孔介质中的压力分布呈线性下降,孔喉结构和泡沫干度是影响泡沫封堵能力的主要因素;泡沫的封堵能力随泡沫干度的增加而先增加后降低,在泡沫干度为85%时达到最强封堵能力。     

Mass transfer with chemical reaction in liquid foam reactors

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid-phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface-active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first-order chemical reaction. The liquid-phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst-order chemical reaction. An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10⁻² m/s to 5 × 10⁻² m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface-active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed. It is observed that gas holdup is insensitive to the type of surface-active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid-phase mass transfer coefficient increases with increase in gas velocity. The surface-active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2-4 times higher than those for conventional packed bed contactors.     

Bubble flow mechanisms in trickle beds—an experimental study using image processing

The mechanisms of bubble motion in concurrent gas-liquid down flow through trickle beds are investigated. The laboratory reactor is a structured quasi-two-dimensional porous medium with an average pore diameter close to the values encountered in trickle beds. The accuracy of the reactor design is demonstrated by hydrodynamic investigations on the reactor scale where it is shown that the flow regimes encountered and the experimental pressure drop are comparable to those observed in trickle beds. The investigations on the pore scale are focused on the dispersed bubble flow regime where the liquid flow is continuous and the gas is divided into elongated bubbles. The bubble motion is recorded with the aid of a high-speed video camera and the images are processed and analysed in a quantitative manner. The investigations clearly show that in dispersed bubble flow, the bubbles are frequently pulsing on the pore scale. The mechanism of this flow pattern is discussed.     

Bubble point pressures of binary methanol/water mixtures in fine‐mesh screens

Binary methanol/water mixture bubble point tests involving three samples of fine‐mesh, stainless steel screens as porous liquid acquisition devices are presented in this article. Contact angles are measured as a function of methanol mass fraction using the Sessile Drop technique. Pretest predictions are based on a Langmuir isotherm fit. Predictions and data match for methanol mole fractions greater than 50% when pore diameters are based on pure liquid tests. For all three screens, bubble point is shown to be a maximum at a methanol mole fraction of 50%. Model and data are in disagreement for mole fractions less than 50%, which is attributed to variations between surface and bulk fluid properties. A critical Zisman surface tension value of 23.2 mN/m is estimated, below which contact angles can be assumed to be zero. Solid/vapor and solid/liquid interfacial tensions are also estimated using the equation of state analysis from Neumann and Good. Published 2013 American Institute of Chemical Engineers AIChE J 60: 730–739, 2014     

Pressure drop measurements of ceramic sponges—Determining the hydraulic diameter

This paper presents experimental results of pressure drop measurements for different solid ceramic sponges. In the experiments, the material, pore sizes and porosity were varied. Furthermore, this data is correlated using an Ergun-type equation. It was possible to obtain Ergun constants for sponges independently of the varied parameters. In the future, the presented pressure drop correlation will provide a simple method for determining hydraulic diameters for solid ceramic sponges with unknown geometric parameters (strut, window and pore diameter,…) based on pressure drop measurements. Furthermore a correlation is given to derive the hydraulic diameter from the ppi (pores per inch) number.     

A comparison of different geometrical elements to model fluid wicking in paper-based microfluidic devices

Recently, microfluidic paper-based analytical devices (μPADs) have outstripped polymeric microfluidic devices in the ease of fabrication and simplicity. Surface tension-based fluid motion in the paper's porous structure has made the paper a suitable substrate for multiple biological assays by directing fluid into multiple assay zones. The widespread assumption in most works for modeling wicking in a paper is that the paper is a combination of capillaries with the same diameter equal to the effective pore diameter. Although assuming paper as a bundle of capillaries gives a good insight into pressure force that drives the fluid inside the paper, there are some difficulties using the effective pore radius. The effective pore radius is totally different from the average geometrical pore radius which makes it impossible to predict wicking in μPADs based on geometrical parameters. In this article, we introduce different analytical and numerical models to investigate the possibility of determining the permeability of the paper, based on geometrical parameters rather than effective parameters. The lattice Boltzmann method is used for numerical simulations. The permeability of each of the proposed models was compared with the experimental permeability. Results indicated that assuming paper as a combination of capillaries and annuluses leads to accurate results that totally depend on average geometrical values rather than effective values. This paves the way for prediction of the fluid wicking only by considering average geometrical pore and fiber diameters.     

纤维毡波折前后初始气泡点变化规律

纤维毡波折变形后孔径发生变化,引起初始气泡点变化.用过滤器渗透性试验仪测定了不同孔径纤维毡波折前后初始气泡点的变化情况.结果表明,纤维毡单重越大,纤维丝径越细,波折后初始气泡点变化越大;相同孔径的纤维毡,在细面形成波峰时比在细面形成波谷时初始气泡点变化大;纤维毡厚度越小,初始气泡点变化越大.     

FLOW THROUGH A HIGHLY POROUS ANISOTROPIC MULTIFILAMENT KNIT

Experimental results for isothermal Newtonian flow through a high porosity anisotropic porous medium are provided. The porous medium is formed by a knitted stainless steel wire mesh rolled up to form a cylindrical plug. This kind of porous medium is generally used as a mist eliminator in the chemical and petroleum industries. Experimental results are compared with pressure drop predictions obtained with a theoretical pore-scale method. The model allows for anisotropy and is applied predictively over both the Darcy and non-Darcy regimes, requiring only that the porosity, dimensions of the wire and characteristic lengths of the plug be known. The predictions compare reasonably well with the experimental results.