开孔金属泡沫内气液两相流动的可视化

开孔金属泡沫内流动特性的研究多局限于局部流动特性的分析,大尺寸（100cm²以上）金属泡沫内气液两相宏观流动特性的研究目前较为缺乏。为了深入认识金属泡沫内气液两相流动特性,本文通过光学可视化手段,对金属泡沫多孔介质薄层内的气/液驱替、液/气驱替两相流动过程进行研究,分析了入侵流体的流速及金属泡沫的孔径对泡沫薄层内两相流动的影响。结果表明：在气/液驱替流动方面,随着空气流速的增大,气液两相的界面形态由毛细指状结构过渡到黏性指状结构,随着泡沫孔径的减小,部分排水现象愈加显著;在液/气驱替流动方面,气液界面较为规则,近似呈锥形,且流速越大,界面锥角越大、长度越小,试验中仅在最小孔径的金属泡沫中捕捉到明显的部分驱替现象,并且随着水流速的减小愈加显著。     

水平矩形管内气液两相流界面波特性

<正>气液两相流中界面波的存在对传热、传质、阻力特性及稳定性都有很大影响。前人有关界面波的研究大多偏重于两相流中界面波的类型及其转变,而对其特征参数变化规律(如振幅、波长、频率和速度等)的研究则很少。但界面波对气液两相流流动阻力和流动结构影响机理的深入研究必须以了解界面波的各特性参数为前提,同时界面波有关特性参数的深入研究也可为气液两相流的数学理论化提供实验基础。 本文以气、水为工质,系统研究了水平矩形管内气液两相流的界面波特性。根据界面波在时域、幅域内的不同特征区别出了各种类型的波并给出了相应的波形和流型图。着重研究了界面波各特征量随气液两相流量变化的变化规律。     

气体分布器结构对气升式环流反应器内气液两相流动的影响

使用欧拉两流体模型研究气体分布器结构对气升式环流反应器内气液两相流动的影响,预测了环己烷氧化反应器内单环结构、三环结构、五环结构的气体分布器时反应器内液相速度分布、气含率分布、液相循环速度以及液相微观混合特性.模拟结果表明,在等量的进气流量下,气体分布器环数增加,液相速度分布和气含率分布更趋均匀;气体分布器环数增加,液相推动力增加,从而使得液相循环速度增加,液相的宏观混合效果增强;气体分布器环数增加,导流筒内外的平均气含率增加.随机游走模型模拟结果表明,气升式环流反应器与普通鼓泡床反应器对气体分布器结构要求不同.     

蛇形微通道气液两相流动特性

以空气、去离子水为实验工质,在θ=50°的Y型混合器内充分混合,利用高速摄像仪对当量直径177.8 μm的小曲率蛇形微通道进行可视化实验,对比了两种气液混合方式(上气下液型、上液下气型)下的流动特性。实验发现的主要流型有弹状流、波状分层流、弥散流等,对此分别研究了气弹的形状和长度、液膜厚度以及气流携带液滴的份额,并提出新的预测液滴含量的关联式。此外,针对这两种不同的混合方式,在弯道处发现圆弧可以诱导产生弹状流,二者均经历拉伸和断裂过程,区别在于后者在拉伸之前,先要进行膨胀。不同的气液混合方式对各相的流动会产生一定的影响,两相流体在通道壁面附近以及弯道处的分布也有所区别。     

旋流器内气液两相流动的理论分析

气-液旋流分离过程是气-液两相的三维强旋流运动。以漂移流动模型和颗粒轨迹方程为基础,采用欧拉-拉格朗日方法建立一种新的气液两相流动机理模型。该模型可以用来直接计算气液旋流分离器内部流场中连续相、分散相(液滴)的速度分布,通过计算能够预测旋流器内部的浓度分布,并通过对影响气液分离效率的主要原因——出口气体中的液滴夹带进行分析计算,预测旋流器的分离性能。     

微通道内液-液两相流研究进展

从流型、传质和应用3个方面,介绍了近年来微通道内液-液两相流的研究进展。液-液两相流型研究内容主要有两部分,即流型的观察、流型谱图的绘制以及考察多种因素对流型的影响,但是具有普适性的流型谱图和流型转变线仍未提出。液-液两相传质研究方法包括实验研究和数值模拟两种,主要研究在液滴流、弹状流和平行流3种稳定流型下的传质过程;且相对于定性研究,定量的传质研究较少。对于微通道内液-液两相流应用研究,主要体现在萃取、材料合成、生物结晶等方面。此外,对今后微通道内液-液两相的流型、传质和应用研究进行了展望,指出需从实验与模拟计算相结合以及拓展微通道内液-液两相流的应用研究两个方面进行深入研究,推进其工业化进程。     

等温气液混合器压降研究

实验研究空气-水两相流体通过等径90°T型管混合器进行混合的压降.结果表明,在实验范围内,混合后气液两相混合物的流动流型为环雾流,其压降主要与两股混合物流的动量比有关.根据混合后气液两相混合物的流动流型,模拟计算空气-水系统的压降,计算结果与实验结果较为吻合.利用该计算模型分析气液流量对混合器压降的影响.     

微细圆管及扁平管内液-液Taylor流动特性的数值研究

微细通道内Taylor流动广泛应用于能源化工领域,为分析其相界面及阻力特性,利用相对坐标系的方法,研究了竖直圆管及扁平管内的液-液Taylor流动,讨论了通道宽高比、Reynolds数（Re）及分散相体积分数对液膜厚度和两相压降的影响。结果表明：圆管内液滴头部和尾部可以膨胀至近似球形,而扁平管内壁面的限制作用较强,液滴呈现扁平状。随Reynolds数增大,两相界面逐渐收缩,液膜厚度逐渐上升。圆管内液膜厚度比较均匀,扁平管内液膜在通道顶部较薄,而圆弧部分较厚。两相压降随Re和宽高比的增大而增大,随分散相体积分数的增大而降低。相比连续相和分散相压降,界面压降所占的比重最高,并依据模拟结果,提出了圆管及扁平管内液-液Taylor流动的压降预测公式。     

微小通道内低Reynolds数液-液两相流动与换热特性实验研究

实验研究了圆形微小通道内液-液两相流的流动和换热特性。选用去离子水为分散相,高黏度二甲基硅油为连续相。通过处理高速摄像所拍摄的可视化图像,总结了液-液两相流流型和液滴的长度/形状特征。并在此基础上考察了低Reynolds数下液-液弹状流对微小通道的换热作用。结果表明,平均Nusselt数随着Reynolds数的增加而增加,且油水比越大传热系数增加幅度越明显。Nu随着含水率的增加而降低。虽然含水率增加会使两相平均热容量提高,但在低Reynolds数下,这种提高被其长液滴内较弱的循环强度所抵消。选用三种不同形式接头在相同混合速度和含水率的情况下生成不同长度的液滴,发现短液滴更有利于换热。相同工况下,液滴长度的优化可以使整体传热系数提高近26%。     

微结构设备内液-液两相流行为研究及其进展

系统介绍和分析了在微结构设备内液-液两相流的不同流型,以及在不同流型条件下两相流动特性和混合性能,并在此基础上对微结构设备在液-液两相反应和分离过程的发展前景进行了展望,指出了该领域今后的主要研究方向。     

Continuous Interfacial Centrifugal Separation and Recovery of Silver Nanoparticles

Continuous-flow separation and recovery of silver nanoparticles (AgNPs) using an annular centrifugal extractor (ACE) is demonstrated. Separation was achieved at the liquid-liquid interface based on the balance between centrifugal force and the solubility of the capping agent. A mathematical model is presented to understand the mechanism in greater detail. The separation of poly(vinylpyrrolidone) (PVP)-coated AgNPs in an ACE using a strong immiscible solvent was performed. The material accumulated at the interface was separated periodically without discontinuing the operation. The method is also suitable for separation of large particles or 1D/2D nanostructures even employing a single annular centrifugal extractor. Stable AgNPs were selected for a detailed antimicrobial activity study.     

微通道内气液(液液)二相流的实验研究进展

综述了微通道内气液(液液)二相流的流型特征.微通道内气液二相流常见的流型为泡状流、弹状流、环状流和翻腾流;液液二相流常见的流型为液滴流、塞状流、平行流及环状流.分析了不同操作条件对气液(液液)二相流行为的影响.介绍了微通道内气液(液液)二相流流型判别谱图,对常用的弹状流、液滴流和塞状流进行了重点介绍.指出了微通道内气液...     

Open-Source CFD Simulations of Liquid–Liquid Flow in the Annular Centrifugal Contactor

Simulation of the fluid dynamics of solvent extraction in centrifugal contactors requires advanced models to account for complex physical phenomena including turbulent free-surface flow and liquid-liquid dispersion physics. The use of an open-source computational fluid dynamics (CFD) framework allows for implementation of advanced models not feasible in commercial CFD applications. The open-source CFD package OpenFOAM has been used to simulate turbulent, multiphase flow in the annular centrifugal contactor, including simulations of the mixing zone (annular region), and of the coupled operation of the mixing and separation (rotor interior) zones. These simulations are based on the Volume of Fluid (VOF) methodology along with Large Eddy Simulation (LES) for turbulence. The results from these simulations compare favorably with previous simulations using a commercial CFD tool and with available experimental data. They also give insight into the requirements for more advanced multiphase models needed to accurately capture flows in these devices.     

Recent progress in hydrodynamic characteristics research and application of annular centrifugal extractors

The annular centrifugal extractor (ACE) integrates mixing and separation. It has been widely used in many industrial fields because of its low residence time, compact structure, and high mass transfer efficiency. Most of the literature has focused on flow instabilities, flow visualization, and computational fluid dynamics simulations. More recently, research on hydrodynamic behavior and structural optimization has received widespread attention. With the development of ACE technology, applications have been broadened into several new areas. Hence, this paper reviews research progress regarding ACE in terms of hydrodynamic characteristics and the structural improvements. The latest applications covering hydrometallurgy, nuclear fuel reprocessing, bio-extraction, catalytic reaction, and wastewater treatment are presented. We also evaluate future work in droplet breakup and coalescence mechanisms, structural improvements specific to different process requirements, scaling-up methods, and stability and reliability after scaling-up.     

Effect of Cylinder Rotation on Flow Characteristics of the Annular Region in Annular Centrifugal Extractor

The flow patterns in the annular region of a 50 mm annular centrifugal extractor (ACE) were studied using phase particle image velocimetry (PIV), by which the distributions of radial velocity, axial velocity, vorticity, turbulent kinetic energy (TKE), and micromixing time of a fluid under different rotating Reynolds numbers were investigated. In the center of the annular region, both the radial and axial velocities of the fluid are close to zero, regardless of the rotating Reynolds number changes. The TKE of the fluid along the radial direction is small at center and large on the edge. The results show that the mixing process mainly occurs at the region near the outer cylinder’s sidewall, and the mixing time in this region is less than that in the internal annular region. Besides, the whole mixing efficiency is proportional to the rotational speed when the speed is below a certain level, and then gradually reaches a plateau when the speed is further increased.     

Experimental study of the hydraulic operation of an annular centrifugal contactor with various mixing vane geometries

The annular centrifugal contactor is a combination mixer/centrifuge that has been developed for solvent extraction processes for recycling used nuclear reactor fuel. The experimental observations presented were part of a simulation‐focused research effort aimed at providing a more complete understanding of the fluid flow within these contactors to enable further advancements in design and operation of future units and greater confidence for use of such contactors in a variety of other solvent extraction applications. Laser doppler velocimetry (LDV), particle image velocimetry (PIV), pressure measurements, and high‐speed video imaging for a range of flow rates and rotor speeds were performed to characterize the flow of water in the annular mixing region of the contactor using three different mixing vane geometries. It was found that the geometry of the mixing vanes has a significant impact on the annular liquid height and general flow in the contactor mixing zone. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Evaluation of Annular Centrifugal Contactors for the Extraction of Acetic Acid from Aqueous Streams

This study investigates the use of annular centrifugal contactors for the liquid-liquid extraction of acetic acid from an acidic aqueous phase into an organic phase consisting of 1.5 M Tributyl Phosphate in n-Dodecane. Initial break time tests were performed in order to investigate the mixing/separation viability of the organic/aqueous system, and after determining that centrifugal contactors could be used to perform the liquid-liquid extraction, hydraulic tests established the combination of rotation rate and throughput which should be used to ensure proper separation of the two outlet phases. Finally, extraction efficiency data was collected to examine the system conditions that provided the most efficient removal of acetic acid.     

用离心萃取器连续逆流提取氢化可的松的研究

采用环隙式离心萃取器进行了提取氢化可的松的研究。用醋酸丁酯从发酵液中萃取氢化可的松 ,其传质过程受扩散因素控制 ,且分配系数随平衡水相浓度的增大而增大。开发了用环隙式离心萃取器连续逆流提取氢化可的松的工艺流程 ,当转速为 340 0～ 380 0r/min ,总流量为 40～ 75mL/min ,V(O ,有机相 )∶V(A ,水相 )为 (0 35～ 0 42 )∶1 0 0时 ,氢化可的松的萃取率为91 0 8%～ 93 16 % ,而厂家现行生产工艺采用的V(O)∶V(A)是 0 7∶1 0 ,氢化可的松的萃取率为90 %。因而 ,新工艺提高了氢化可的松的萃取率 ,降低了萃取剂耗量     

Synergistic Extraction of Lanthanides in a Liquid-Liquid Countercurrent Centrifugal Extractor

We have developed a liquid-liquid countercurrent centrifugal extractor that induces Taylor vortices in the annular fluid region. To demonstrate extraction of multiple species (Nd/Sm/Eu/Gd/Dy) with N,N,N′,N′-tetraoctyl diglycolamide (TODGA), additional chemical agents, such as a surfactant (sodium bis(2-ethylhexyl) sulfosuccinate (AOT)), a synergist (nonanoic acid) and a masking agent (N,N,N′,N′-tetraethyl-3,6-dioxaoctane-1,8-diamide (DOODA(C2))) were employed. When only TODGA was utilized, extraction performance was not effective due to the insufficient dispersion even under a high rotating speed. By combining TODGA and other chemical agents, the separation performance was improved considerably in the countercurrent flow of aqueous and organic phases due to the synergistic effect and improved dispersion.     

Hydraulic characteristics of n-octanol/aqueous solution systems in a 25-mm annular centrifugal extractor

ABSTRACT

The hydraulic characteristics of the n-octanol/H₂O, n-octanol/1 M HNO₃ solution, and kerosene/H₂O systems in the 25-mm annular centrifugal extractor (ACE) were investigated to provide guidance for optimizing the operation parameters and heavy phase weir diameter of the 25-mm ACEs used in a production line to extract ¹³⁷Cs and ⁹⁰Sr using the calixcrown ether cesium extraction (CECE) and crown ether strontium extraction (CESE) processes, respectively, from high-level liquid waste (HLLW). The effects of the flow ratio (A/O), rotor speed, and heavy phase weir diameter on the hydraulic characteristics of n-octanol/aqueous solution systems in the 25-mm ACE are complex. Moreover, the hydraulic characteristics of n-octanol/aqueous solution systems are very different from those of the kerosene/H₂O system in the 25-mm ACE. All results showed when the 25-mm ACEs will be used in the CECE and CESE processes, the heavy phase weir diameter and rotor speed should correspond to ranges of 12.5 to 13.0 mm and 3000 to 3500 r/min, respectively, to meet the requirement the total flow rate of 3 L/h in the production line for the recovery of ¹³⁷Cs and ⁹⁰Sr.