Kinetic Mass Transfer Between Non-aqueous Phase Liquid and Gas During Soil Vapor Extraction

The mass transfer between non-aqueous phase liquid(NAPL) phase and soil gas phase in soil vapor extraction(SVE) process has been investigated by one-dimensional venting experiments. During quasi-steady volatilization of three single-component NAPLs in a sandy soil, constant initial lumped mass transfer coefficient (λgN,0) canbe obtained if the relative saturation (ξ) between NAPL phase and gas phase is higher than a critical value (ξc), andthe lumped mass transfer coefficient decreases with ξ when ξ＜ξc. It is also shown that the lumped mass transfercoefficient can be increased by blending porous micro-particles into the sandy soil because of the increasing of theinterfacial area.

Experimental Study of the Distribution of Au and Cu in Aqueous Vapor Phase at High Temperatures and Its Role on Ore-forming Transportation

This study focuses on experiments of Au and Cu dissolved in vapor phase in hydrothermal fluids. Experiments prove that Au and Cu can re-distribute in vapor phase and liquid phase during separation of Au- and Cu-bearing supercritical fluids to vapor and liquid phases. These experimental results can illustrate some ore geneses, where boiling phenomena of ore fluids were found. Au- and Cubearing NaHCO3-HCl solutions were heated up to more than 350℃ in the main vessel, and then passed through a phase separator in a temperature range from 250℃ to 300℃, separated into vapor and liquid phases. We collected and analyzed the liquid and vapor samples separately, and found that Au and Cu dissolved and distributed in vapor phase. In some cases, the concentrations of Au and Cu in vapor are higher than those in liquid phase. Those experiments are used to interpret field observations of fluid inclusion data of some Au and Cu deposits, and demonstrate that some Au and Cu ore deposits are derived from metals transportation in vapor phase.

Interface evolution of TiAl/Ti6242 transient liquid phase joint using Ti, Cu foils as insert metals

The interface evolution of TiAl/Ti6242 joint produced by transient liquid phase(TLP) bonding with Ti, Cu foils as insert metals was investigated. The results show that the surface oxide layer on TiAl plays a very important role in the formation process of the joint. A ‘bridge’ effect is observed because of the presence of the oxide layer on the surface of TiAl. The diffusion behavior of Cu atoms in TiAl is strongly controlled by the vacancies beneath the surface of TiAl. Based on the interface diffusion and interface wettability, a mechanism for the effect of bonding pressure, bonding temperature, holding time and stacking sequence of the insert foils on the joint formation process were proposed.

Effect of the formation process of transient liquid phase (TLP) on the interface structure of TiAl joints

TiAl has been joined employing the transient liquid phase （TLP） bonding with Ti combined with Cu, Ni or Fe foils. Experimental results showed that though the interface structures of the joints are quite different, all the joined zones are composed of five sublayers, i.e. two diffusion zones, two interfacial zones and an interlayer. It has been convinced that the formation process of the transient liquid phase controls the diffusion behavior of melting point depressant （MPD） Cu, Ni, and Fe atoms, which leads to form different interface structures of the joints.

Microscale Infrared Observation of Liquid-Vapor Phase Change Process on the Surface of Porous Media for Loop Heat Pipe

Loop Heat Pipe (LHP) performance strongly depends on the performance of a wick that is porous media inserted in an evaporator. In this paper, the visualization results of thermo-fluid behavior on the surface of the wick with microscopic infrared thermography were reported. In this study, 2 different samples that simulated a part of wick in the evaporator were used. The wicks were made by different two materials: polytetrafluoroethylene (PTFE) and stainless steel (SUS). The pore radii of PTFE wick and SUS wick are 1.2 μm and 22.5 μm. The difference of thermo-fluid behavior that was caused by the difference of material was investigated. These two materials include 4 different properties: pore radius, thermal conductivity, permeability and porosity. In order to investigate the effect of the thermal conductivity on wick’s operating mode, the phase diagram on the q-keff plane was made. Based on the temperature line profiles, two operating modes: mode of heat conduction and mode of convection were observed. The effective thermal conductivity of the porous media has strong effect on the operating modes. In addition, the difference of heat leak through the wick that was caused by the difference of the material was discussed.

Nanoscale materials transformations revealed by liquid phase TEM

Nanoscale materials often undergo structural,morphological,or chemical changes,especially in solution processes,where heterogeneity and defects may significantly impact the transformation pathways.Liquid phase transmission electron microscopy(TEM),allowing us to track dynamic transformations of individual nanoparticles,has become a powerful platform to reveal nanoscale materials transformation pathways and address challenging issues that are hard to approach by other methods.With the development of modern liquid cells,implementing advanced imaging and image analysis methods,and strategically exploring diverse systems,significant advances have been made in liquid phase TEM,including improved high-resolution imaging through liquids at the atomic level and remarkable capabilities in handling complex systems and reactions.In the past more than a decade,we spent much effort in developing and applying liquid phase TEM to elucidate how atomic level heterogeneity and defects impact various physicochemical processes in liquids,such as growth,self-assembly of nanoparticles,etching/corrosion,electrodeposition of alkali metals,catalyst restructuring during reactions,and so on.This article provides a brief review of the liquid phase TEM study of nanoscale materials transformations,focusing on the growth of nanomaterials with distinct shape/hierarchical structures,such as one-dimensional(1D)growth by nanoparticle attachment,two-dimensional(2D)growth with nanoparticles as intermediates,core-shell structure ripening,solid-liquid interfaces including those in batteries and electrocatalysis,highlighting the impacts of heterogeneity and defects on broad nanoscale transformation pathways.

Phase difference and interference between reflected cylindrical wave and head wave at a liquid/solid interface

The reflected field of pulsed cylindrical waves from a liquid-solid interface is studied by the numerical method and the experimental method. The reflected field is calculated and shown in gray pictures. The calculated incident angles θn (n=1, 2, 3, ...) of a series of minimums (or nulls) on the reflected wavefront are presented. The measured angle of the minimum from Schlieren photograph is consistent with that by calculation. The appearance of minimums is explained by the interference between the reflected wave and the head wave, and by the radiated dissipation of the head wave. The leading phase angle of the head wave to the reflected wave is proved to be about 3π/4 by the numerical calculation.

Generalized Van der Waals Equation for Liquid-Vapor Equilibria in a Stationary Gravitational Field

The behavior of liquids undergoing phase transition in the gravitational field is studied by considering the generalized Van der Waals equation. Considering the two simple models for liquid-vapor boundary of a pure classical fluid, the generalized Van der Waals equation shows how the three critical parameters (critical temperature, critical volume and critical pressure), suffice to describe the reduced state parameters (reduced temperature, reduced volume and reduced pressure), the concentration profile and the liquid-vapor boundary position, which can be used to observe transition phenomenon. This model shows how the form of the equation can influence the vertical phase separation induced by the stationary gravitational field, and on the gas condensation effects.

微重力条件下PCM液桥内固液相变过程及热毛细对流数值模拟

为揭示微重力条件下PCM液桥相变过程流动特征及相变演化规律,建立PCM液桥数理模型,采用数值模拟的方法系统研究了不同工况下PCM液桥相变过程中固液界面的演化过程,分析不同高径比和温差对液桥形状、固液界面演化规律、相变速度和热毛细流动的影响.研究结果显示,在大温差条件下热毛细流动更加强烈,处于外部壁面处的相变材料的相变速度也会更快,外壁处的相变界面与壁面的夹角会更小.大高径比条件下会有同样的效果,同时也会产生更多的涡胞结构,热毛细对流效果更明显.结果表明,微重力条件下通过流体界面热毛细效应强化PCM相变是一种有效的方法.

液态金属在电子热控中的应用进展与挑战

液态金属作为当下科学和工业前沿的璀璨明珠,不仅是实际应用中不可或缺的重要组成部分,更是一个充满未知奇迹的探索领域。其独特的物理性质使得它在电子热控方面备受瞩目。文中剖析了热控应用中至关重要的典型液态金属的物理参数和性能,深入挖掘了液态金属在电子热控中的应用场景,介绍了它作为热界面材料、相变储能材料和循环工质的现状和研究进展,并进一步阐述了液态金属在电子热控应用中面临的主要技术挑战,提出了应对这些技术挑战的技术途径,指出了液态金属未来的研究方向。

Liquid vaporization under thermodynamic phase non-equilibrium condition at the gas-liquid interface

Liquid vaporization under thermodynamic phase non-equilibrium condition at the gas-liquid interface is investigated over a wide range of fluid state typical of many liquid-fueled energy conversion systems. The validity of the phase-equilibrium assumption commonly used in the existing study of liquid vaporization is examined using molecular dynamics theories. The interfacial mass flow rates on both sides of the liquid surface are compared to the net vaporization rate through an order-of-magnitude analysis.Results indicated that the phase-equilibrium assumption holds valid at relatively high pressures and low temperatures,and for droplets with relatively large initial diameters(for example,larger than 10 μm for vaporizing oxygen droplets in gaseous hydrogen in the pressure range from 10 atm to the oxygen critical state). Droplet vaporization under superheated conditions is also explored using classical binary homogeneous nucleation theory,in conjunction with a real-fluid equation of state. It is found that the bubble nucleation rate is very sensitive to changes in saturation ratio and pressure;it increases by several orders of magnitude when either the saturation ratio or the pressure is slightly increased. The kinetic limit of saturation ratio decreases with increasing pressure,leading to reduced difference between saturation and superheat conditions. As a result,the influence of nonequilibrium conditions on droplet vaporization is lower at a higher pressure.

铝钢双金属液固复合铸造研究现状

随着资源短缺、环境污染等问题日益凸显,节能减排成为全世界追逐的目标,汽车工业中用轻质铝合金代替传统的钢或铸铁的趋势越来越明显。铝钢双金属兼具铝合金和钢或铸铁的性能优势,是极具潜力的缸体、活塞等发动机零部件材料。双金属复合铸造因具有工艺简单、结构受限小等优点而被广泛关注。铝钢液固双金属复合铸造的主要挑战包括基体表面易氧化、Al对Fe润湿性差和界面处形成硬脆金属间化合物,导致双金属结合性能不理想。近年来,研究人员在提高铝钢液固复合铸造双金属界面结合强度方面开展了大量研究。本文对常用的铝钢液固复合铸造工艺及其质量影响因素进行了概括,并总结了近年来铝钢液固复合铸造双金属界面相组成和演变过程的研究现状,最后对铝钢液固复合铸造在提高界面结合强度方面的研究进展进行了综述。在此基础上,本文对铝钢双金属液固复合铸造未来研究和发展方向进行了总结和展望。

离子液体界面修饰的高效稳定FAPbI_(3)钙钛矿太阳能电池

碘铅甲眯(FAPbI_(3))钙钛矿太阳能电池因其优异的光伏性能而受到广泛关注,但器件的长期稳定性仍然是FAPbI_(3)太阳能电池的关键问题。FAPbI_(3)黑色钙钛矿相在室温下会相变为黄色非钙钛矿相,且水分会加速这一相变。界面工程是提高钙钛矿太阳能电池稳定性的常用方法之一。作为绿色溶剂,离子液体被认为是有毒界面修饰剂的潜在替代品,这也提高了它们的商业可行性,并加速了它们在可再生能源市场的应用。本研究利用具有低挥发性、低毒性、高导电性和高热稳定性的离子液体1-乙基-3-甲基咪唑四氟硼酸盐(EMIM[BF_(4)])来修饰钙钛矿太阳能电池的电子传输层和钙钛矿层之间的界面。离子液体的引入不仅减少了界面缺陷,而且提高了钙钛矿薄膜的质量。密度泛函理论计算表明,离子液体与钙钛矿表面之间存在较强的界面相互作用,有利于降低钙钛矿表面缺陷态密度,稳定钙钛矿晶格。除钙钛矿薄膜缺陷外,溶液处理的SnO_(2)也存在表面缺陷。在SnO_(2)表面的缺陷产生缺陷态,也会导致能带对准问题和稳定性问题。密度泛函理论计算表明,有离子液体的表面间隙态比没有离子液体的表面间隙态小,这种减弱的表面间隙态表明表面区域载流子复合减少,有利于提高器件性能。因此,我们实现了功率转换效率大于22%的离子液体修饰的FAPbI_(3)钙钛矿太阳能电池(对照21%)。在相对湿度~20%的干箱中存放1800h以上后,冠军器件保留了初始状态的~90%,而控制器件降解为非钙钛矿黄色六方相(δ-FAPbI_(3))。

5-氯-2-戊酮与环丙基甲基酮物性及汽液相平衡

测定5-氯-2戊酮和环丙基甲基酮的物化性质:密度、黏度、摩尔体积、热膨胀系数和表面张力。测定5-氯-2-戊酮(1)+环丙基甲基酮(2)二元体系的汽液相平衡(VLE),并应用Aspen Plus V11中Van Laar方程、Wilson方程和NRTL方程对实验数据进行关联,回归得到二元交互参数。实验结果通过热力学一致性检查。该研究不仅补充了汽液相平衡数据库,也为5-氯-2-戊酮与环丙基甲基酮的分离提供热力学数据。

气液两相流分配器参数敏感性分析与优化

针对制冷系统气液两相流分配不均引起的多流路蒸发器能效低下,以及分配器结构设计不合理问题,基于六面体网格和Euler-Euler模型,构建了分配器中制冷剂气液两相流动模型,详细分析了制冷剂在分配器中的流动特性,研究了不同工况下腔体高度、腔体直径以及支管插入深度等参数对分配不均匀度的影响规律,并结合田口法进行敏感性分析及参数优化,得到了各参数的影响权重及最优参数组合。数值结果表明:随着腔体高度与直径的增大,气液两相流混合效果得到改善,分配不均匀度逐渐下降;随着插入深度的增大,分配器不均匀度先降低后增大,插入深度最优值为5 mm;随着质量流量的增大,腔体高度与插入深度的贡献逐渐增大,而腔体直径的贡献逐渐减小,表明分配均匀性对腔体直径的依赖程度降低;相对于基准案例,所得最优组合的不均匀度降低了6.6%~19.3%。该研究可为抑制气液两相流相分离和分配器结构设计提供理论基础及数据支撑。

异质固液界面中多界面态的原子模拟研究

在晶界和固体表面系统中,针对界面“complexion”(或界面相、界面态)转变及其调控相关的研究,近年来呈现出持续增长的关注趋势.与此同时,这些界面相之间的转变问题,在异质固液界面体系中尚未得到足够的关注.使用分子动力学模拟方法预言了处于Pb熔点温度之上,Cu(111)/Pb(L)固液界面体系中存在的多界面相共存的界面状态;观察到4种单原子层的界面状态,即2种界面CuPb层状合金液相以及2种界面预凝固的Pb层状固相,共存于固体Cu和液体Pb之间的双原子界面层内;通过计算界面相在面内共存的各种性质空间分布,模拟出了该体系多界面相共存的力学、热力学和动力学性质的不均匀性和面内各向异性;计算获得的界面态热力学与动力学性质数值显著区别于固相Cu和液相Pb的相应性质.另外,测量得到的Cu(111)/Pb(L)固液界面态共存的“相平衡”条件具有共晶二元合金相图特征,而不是CuPb合金的偏晶相图.故所报道的数据有望为调节异质形核和润湿过程提供新的理论思路.

用于电催化合成过氧化氢的碳电极综述

通过双电子(2e-)途径的电催化氧还原方式能够即时合成过氧化氢(H_(2)O_(2)),远超传统的蒽醌工艺。近年来,碳电极因具有良好的催化效果和优越的稳定性在电催化合成H_(2)O_(2)方面受到越来越多的关注。本综述结合材料改性与润湿性调整,从三相界面的角度考虑与H_(2)O_(2)合成速率及使用寿命的关系。介绍了碳电极的结构与电催化合成H_(2)O_(2)的原理,包括单质炭材料、无金属催化剂、贵金属催化剂与非贵金属催化剂4种主流催化剂;金属阳极与电解液对于三相界面的影响;碳电极润湿性与三相界面的关系,指出侧重于提高2e-途径选择性的改性方式也会对电极润湿性造成影响。此外,合理地设计电器原件与提升碳电极合成H_(2)O_(2)功效的关系。最后,讨论了当前碳电极电催化合成H_(2)O_(2)所面临的问题与未来的研究方向。

液态金属快堆螺旋管蒸汽发生器一、二次侧耦合传热数值研究

螺旋管蒸汽发生器是液态金属快堆中能量传递的核心设备,其运行的稳定性、安全性对核电站的运行有至关重要的影响。为此,本文构建了液态金属快堆螺旋管蒸汽发生器一次侧、二次侧耦合传热的三维数值模型,分别基于经济合作与发展组织核能署(The Organisation for Economic Co-operation and Development,OECD/NEA)物性手册和美国国家标准与技术研究院(National Institute of Standards and Technology,NIST)数据库建立液态金属和水-水蒸气变物性计算关联式,采用Lee相变模型计算二次侧水-水蒸气蒸发过程中两相间的质量传递。基于实验数据,分别对本文模型一次侧传热以及二次侧传热的计算可靠性进行了验证。最后以铅铋快堆为例,研究了不同一次侧进口参数下蒸汽发生器一、二次侧之间的耦合传热特性,并与传统水冷堆进行了对比。结果表明:在同等条件下,相比于传统水冷堆,一次侧采用铅铋液态金属时,一、二次侧之间的壁面热流密度明显提升,热流密度峰值可达1439.97 kW·m^(-2),比水冷堆相应数值提升5~6倍,这导致二次侧管内气相蒸发过程明显加剧,体积含气率急剧上升;同时,一、二次侧之间的沿程热流密度分布更加不均匀,沿程热流密度分布相对偏差值比水冷堆相应数值增大3~4倍。随着一次侧进口铅铋温度从350℃增大到450℃,一、二次侧之间的壁面热流密度随之增大,对应的热流密度峰值从950.7 kW·m^(-2)增大到1439.97 kW·m^(-2),提升约1.5倍,同时一、二次侧之间的沿程热流密度分布更加不均匀,不均匀度增大20%。

探索微纳尺度润湿动力学:长针式原子力显微镜的应用与进展

“如何在微观层面测量界面现象”是微纳尺度实验流体力学的关键科学问题,被列入世界前沿125个科学问题名单(Sanders S,Science,2021).由于光学衍射极限的限制,传统光学手段很难直接测量微纳尺度下的流动与界面现象.利用原子力显微镜的精准操控和小尺度力学测量等优势,结合长针式探针组装成的微流变计可以直接测量气-液-固三相接触线上的毛细力,并监测探针在垂直方向运动中力的动态变化.通过该技术手段,可以实现对流体界面的动力学行为以及各类材料在液体环境中力学性质在微纳尺度的精确表征.文章将系统介绍长针式原子力显微镜技术的实验原理和方法,及其在微纳尺度非理想界面润湿动力学中的最新研究进展,包括低能垒表面毛细力的速度依赖性与非对称性、无序粗糙表面接触线黏滑运动的统计学规律、柔性表面接触线动力学的状态与速度定律、以及离子液体-金属界面处电场对接触角迟滞的调控等,最后展望了该技术在新兴领域中的应用.该实验手段为检验各类理论模型与数值模拟提供了可信数据,为探究界面上复杂现象的物理本质提供参考.

池态沸腾孤立气泡生长数值模拟

为研究池态沸腾孤立气泡生长过程,该文提出了一种新的相变模型。该相变模型优化了气液界面面积计算方法、提高了相变传质精度并能捕捉池态沸腾中清晰气液界面。采用新相变模型研究了池态沸腾内气泡生长的速度、温度、压强变化。结果表明,池态沸腾中气泡在生长时,气泡内部的速度始终大于气泡外部的速度,而界面温度从过热降至饱和。然而气泡内部的压强呈现先增加后减小,最后出现负压的情况。