金属泡沫内固-液相变数值模拟研究

本文利用多孔介质的体积平均模型,建立了金属泡沫内固-液相变的两方程数学物理模型,该模型考虑了熔化液态石蜡自然对流的影响、石蜡与泡沫局部非热平衡效应。模拟研究了熔化过程中不同泡沫孔隙率下液态石蜡内部的速度场、相界面位置随时间的变化规律,通过研究石蜡温度场和泡沫温度场的差异,证实了采用两方程模型的必要性。     

一维液态泡沫渗流实验研究及表面能和粘性耗散分析

液态泡沫由大量气泡密集堆积在微量表面活性剂溶液中形成，是远离平衡态的软物质. 泡沫强制渗流在微观上是指以恒定流率输入的液体在气泡间隙内的微流动过程，是影响泡沫稳定的主要因素之一. 采用在表面活性剂溶液中添加微量色素以显示泡沫中液体流动的方法，确定了透射率与液体分率的对应关系，测量得到了一维液态泡沫强制渗流中渗流波传播规律以及液体分率的演变规律；理论推导了泡沫基本单元，即开尔文单元结构(Kelvin cell)的粘性耗散能表达式，并依据Surface Evolver软件计算得到了不同液体分率时开尔文单元结构对应的的表面能，并计算出了与实验系统对应的开尔文单元结构的表面能和粘性耗散. 基于开尔文单元结构内液体分率演变的准静态假设，分析了表面能和粘性耗散的演变规律.     

金属泡沫中填充石蜡的相变换热特性实验研究

本文对金属铜泡沫填充石蜡的相变换热特征进行了实验研究,通过测试试件加热面及内部的温度响应曲线,分析了金属泡沫填充及自然对流对石蜡非稳态相变换热过程的影响。研究结果表明,采用顶部加热方式时,石蜡内部的换热以纯导热为主,而采用底部加热时,液态石蜡内的自然对流作用使相界面移动速度更快,试件内部温度一致性更好,同时在相变对流区可实现对加热面的温度控制。金属泡沫的填充可强化石蜡内的导热但抑制液态石蜡的自然对流,前者使得试件加热面温升减缓,相界面移动加快,后者则导致底部加热时石蜡的相变区分为相变导热区和相变对流区。金属泡沫的导热强化能力在试件换热中占据主导作用。     

液晶及其应用

 液晶是１８８８年由奥地利的Ｆ．Ｒｅｉｎｉｔｚｅｒ发现的．他把各向同性的胆甾醇苯酸酯晶体加热到１４５．５℃时,它熔融成为各向异性的混浊液体．继续升温到１７８．５℃,混浊液体突然变为清亮的液体．这个由混浊到清亮的过程是可逆的．这说明在各向同性的国相和各向同性的液相之间存在着一个各向异性的液态中介相．把这个各向异性的液态中介相叫做液晶相．凡是能出现液晶相的物体统称为液晶．混浊的胆甾醇苯酸酯液体就是一种液晶．由于液晶具有各向异性而且是液态,所以液晶必然是由各向异性的分子构成,而且分子倾向于定向排列．各向同性分子构成的液态是不可能出现各向异性的．液晶分子有棒形,盘形和碗形三种形状．     

第一届全国液态物理学术会议报告选登(Ⅰ)液态物理发展展望

第一届全国液态物理学术会议报告选登（Ⅰ）液态物理发展展望陆坤权（中国科学院物理研究所，北京１０００８０）１液态物理是认识自然界基本物态的基础学科液态物质是物质世界的重要组成部分，在自然界、生命体和日常生活中大量存在．作为物质存在的一种基本形态，与固...     

液态金属结构研究新进展

文章介绍了用内耗方法研究金属液态结构的新进展，发现了随温度变化金属液态结构发生不连续的变化，并经差热分析、X射线衍射等实验证实了这种变化．这对认知金属液态结构提供了新的实验依据。     

新液态金属实验回路

本文报道液态金属实验回路的安全技术改造。改造完毕后的回路消除了原回路的周有安全隐患．改善了可调恒定磁场的稳定性，提升了数据采集和处理系统的性能和可靠性。安全改造后的新液态金属实验回路具备了开展液态偏滤器和液态包层相关的磁流体动力学效应（MHD）及其热工水力学方面的研究条件。     

纯铝熔体微观结构演变及液固相关性研究…

对液态Ａｌ在不同冷速下的微观结构及其转变机制进行了分子动力学模拟,模拟采用紧束缚势,得到了不同温度、不同冷速下,Ａｌ的双体分布函数;采用ＨＡ键型指数法统计了各种小原子团在不同温度下所占比例,得到原子组态变化的重要信息．结果表明,在冷却速率较慢时,液态金属Ａｌ最终形成晶态,当冷却速率较快时,液态Ａｌ最终形成非晶态;液态金属中的键对是液态Ａｌ的基本构成单元,液态Ａｌ在形成晶体时,１４２１,１４２２键对起非常重要的作用;而１５５１,１５４１键对对非晶的形成有重要的影响 关键词：     

VES—CO2清洁泡沫压裂液携砂性能实验研究

在大型高压泡沫压裂液实验回路上,对VES—C02清洁泡沫压裂液的携砂性能进行了实验研究。分析了携砂泡沫压裂液流动时临界沉降速度的产生原因,并根据实验结果分析了温度、泡沫质量及支撑剂浓度对临界沉降流速的影响。临界沉降流速随温度的升高而增大,随泡沫质量和支撑剂体积浓度的增大而减小,研究发现当支撑剂浓度大于0．25时,开始出...     

泡沫铝吸声板高新技术成果转化通过专家认定

吉林工业大学和上海众汇泡沫铝材有限公司联合开发的新型泡沫铝吸声板高新技术成果转化认定会于200O年5月31日在上海举行,上海市南汇县科委主持了认定会．泡沫策吸声极采用加压渗流法工艺制成厚度为681020、50、100（mm）板材,每块现格250X250500X500、500X10001000X1500（mm2）不等,有各种颜色可供选择．泡沫铝吸声板具有高空隙率、高通孔率、吸声、屏蔽、不燃、耐温、耐潮、质轻、抗老化、防眩、无污染等特点,是一种新型无纤维环保型吸声板材,平均吸声系数大于05．可广泛应用于建筑声学和噪声控制工程中,例如影剧院、体育馆、游泳…     

Dry microfoams: formation and flow in a confined channel

We present an experimental investigation of the agglomeration of microbubbles into a 2D microfoam and its flow in a rectangular microchannel. Using a flow-focusing method, we produce the foam in situ on a microfluidic chip for a large range of liquid fractions, down to a few percent in liquid. We can monitor the transition from separated bubbles to the desired microfoam, in which bubbles are closely packed and separated by thin films. We find that bubble formation frequency is limited by the liquid flow rate, whatever the gas pressure. The formation frequency creates a modulation of the foam flow, rapidly damped along the channel. The average foam flow rate depends non-linearly on the applied gas pressure, displaying a threshold pressure due to capillarity. Strong discontinuities in the flow rate appear when the number of bubbles in the channel width changes, reflecting the discrete nature of the foam topology. We also produce an ultra flat foam, reducing the channel height from 250 μm to 8 μm, resulting in a height to diameter ratio of 0.02; we notice a marked change in bubble shape during the flow.     

Analysis of RDX-TAGzT pseudo-propellant combustion with detailed chemical kinetics

A detailed model of steady-state combustion of a pseudo-propellant containing cyclotrimethylene trinitramine (RDX) and triaminoguanidinium azotetrazolate (TAGzT) is presented. The physicochemical processes occurring within the foam layer, comprised of a liquid and gas bubbles, and a gas-phase region above the burning surface are considered. The chemical kinetics is represented by a global thermal decomposition mechanism within the liquid by considering 18 species and eight chemical reactions. The reactions governing decomposition of TAGzT were deduced from separate confined rapid thermolysis experiments using Fourier transform infrared spectroscopy and time-of-flight mass spectrometry. Within the gas bubbles and gas-phase region, a detailed chemical kinetics mechanism was used by considering up to 93 species and 504 reactions. The pseudo-propellant burn rate was found to be highly sensitive to the global decomposition reactions of TAGzT. The predicted results of burn rate agree well with experimental burn-rate data. The increase in burn rate by inclusion of TAGzT is due in part from exothermic decomposition of the azotetrazolate within the foam layer, and from fast gas-phase reactions between triaminoguanidine decomposition products, such as hydrazine, and oxidiser products from the nitramine decomposition.     

Dynamics of coarsening foams: accelerated and self-limiting drainage

The evolution of a foam is determined by drainage flow of the continuous (liquid) phase and coarsening (aging) of the dispersed phase (gas bubbles). Free-drainage experiments with slow- and fast-coarsening gases show markedly different dynamics and elucidate the importance of the coupling of the two effects. Strong coarsening leads to drainage times that are shorter (accelerated drainage) and independent of the initial liquid content (self-limiting drainage). A model incorporating the physics of both drainage and diffusive coarsening shows quantitative agreement with experiment.     

液体泡沫对激光的伪装性能分析

为了研究液体泡沫的激光伪装应用,实验分析了液体泡沫对1.06 m激光的伪装性能。采用对比试验方法测得了不同液体泡沫结构参数下的1.06 m激光回波衰减值,结果显示,衰减值最高可达66%,最低为36%。结合激光伪装要求,以草地和钢板为例,理论计算分析了液体泡沫用来实现1.06 m激光伪装可行性。结果表明,使用2 cm厚液体泡沫对钢板进行伪装,激光回波衰减达到36%,在草地背景伪装要求的30%~40%范围内。说明液体泡沫具有较好的1.06 m激光伪装性能,利用液体泡沫可实现激光伪装和地面目标有效防护。     

Application of X-ray radioscopic methods for characterization of two-phase phenomena and solidification processes in metallic melts

X-ray attenuation techniques are an important diagnostic tool for investigating liquid metal two-phase flows or solidification studies in metallic alloys. X-ray visualization enables a general, intuitive understanding of flow phenomena or pattern formation in opaque liquid metal systems. Real-time and in-situ observations of the density distribution within thin solidifying samples achieve a spatial resolution of a few microns and contribute significantly to an improved understanding of dendritic growth processes. Moreover, X-ray radioscopy is a useful tool for a non-invasive, in-situ visualization and characterization of gas bubbles in nontransparent melts or for observations of the formation of metal foams. In this paper we consider three different fields of application which are under intensive investigation at HZDR and TUD: the bottom-up solidification of Ga-In alloys under the influence of buoyancy-driven and electromagnetically driven convection, the injection of Ar gas into liquid GaInSn, the study of Al foams with respect to foam formation and the characterization of their internal structure.     

气泡在液态金属搅拌流场中运动与变形的影响因素分析

用"准三维"数值模拟方法研究吹气发泡法制备泡沫铝的过程中,单个气泡在铝熔液搅拌流场中的运动与变形.液体流场采用多重参考系法进行三维模拟,对气泡运动的二维模拟则在三维流场中的一个通过搅拌轴的特征平面上进行.这样既能捕获气泡在搅拌流场中运动的基本特征,又能大大降低计算成本.应用VOF方法对气液两相之间的界面进行追踪.通过改变过程中的转速,气泡初始速度、位置和尺寸.以及表面张力和液体粘度,分析了这些因素对于气泡运动与变形的影响.     

Foam imbibition in microgravity

We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a Hele-Shaw cell. The bubble edge width ℓ is measured by image analysis. The penetration of the liquid in the foam, the foam imbibition, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes. The motion of bubbles needed for the foam inflation is a slow two-dimensional process with respect to the one-dimensional capillary rise of liquid. The foam is found to imbibes faster than it inflates. Received 20 May 2002 / Received in final form 21 January 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: herve.caps@ulg.ac.be     

Evaluation of the surface properties of PTFE foam coating filter media using XPS and contact angle measurements

A newly developed PTFE foam coating filter was developed which can be used for hot gas cleaning at temperatures up to 250 °C. The emulsion-type PTFE was coated onto a woven glass fiber using a foam coating method. The filter surface was closely examined using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The XPS results were used to determine the binding force between the carbon and fluorine of PTFE, which imparts coating stability to the filter medium. More than 95% of the bonds of the PTFE foam coating filter were between carbon and fluorine, and this filter demonstrated excellent hydrophobic and good oleophobic properties at the same time. The contact angles of liquid droplets on the filter surface were used to predict the potential wetability of the filter against water or oil. In addition, the very low surface free energy of the filter medium, which was evaluated using the Owens-Wendt method, demonstrates a very stable surface and a high de-dusting quality.