大输量多相混输管路气液两相流实验研究

为了研究大输量条件下多相混输管路的流动特性,以水和空气为实验介质,在长江大学多相流实验平台上进行了水平状态的高气液量两相流模拟实验研究。实验采用内径为60 mm、长9.4 m的透明有机玻璃管,并利用高速摄像仪记录实验过程中的流型。通过对实验流型进行整理,将水平管内的气液两相流流型划分为分层流、泡状流、段塞流和环状流,并与典型的Mandhane流型图进行对比分析。另外,对实验范围内的几种典型流型下的压降梯度变化规律进行了研究,泡状流区域压降梯度随气流速的增大而减小,段塞流区域压降梯度随气流速的增大而缓慢增大,环状流区域压降梯度随气流速的增加而继续增大。     

微通道分流弹状流的界面过程及压力演变规律

弹状流分流不仅能调控两相流流型从而强化传热,同时也是生物化工、制药行业的传统过程。针对壁面微通道分流液相、调控两相流型的过程进行数值模拟,获得局部参数变化规律,是获得两相流流型演变机理的基础。采用VOF模型耦合动态自适应网格精准追踪气液界面,模拟气液界面在分液口的界面运动;获得轴向及壁面静压、动压的演变规律。通过模拟可知微通道分流弹状流的关键是气弹在分液口的类活塞运动;同时由于界面拉普拉斯压力差的存在,弹状流压降具有不连续性;且此不连续压力随气弹在分液口的类活塞运动具有周期波动性。而弹状流液桥部分的局部压降是影响总压降的关键;近气弹头部的液相区压降显著,近气弹尾部的液相区域由于液速降低其压降明显衰弱;此为弹状流有别于其他两相流流型的压降特点。     

新型复合T型管对液液二相流的分离

T型管分离器是一类新型的二相流分离器,具有集约、连续、简单、经济、安全以及安装、更新、维护方便等优点,缺点是简单T型管作为分离器在分离二相流时的分离效率往往不高,只能起到部分分离的作用。新型复合T型管是对简单T型管的一种改进,以期能提高二相流的分离效率。以煤油和水为液液二相工作介质,用主管水平,侧支管垂直向上的简单T型管和复合T型管作为二相流分离器,在分层流和有混合界面的分层流的二相流型条件下,进行二相流的相分离实验。实验结果表明:2种流型下复合T型管对二相流的分离效果都比简单T型管好,增加复合T型管的连接管数,能进一步提高分离效率;在分层流时连接管数为5管及以上的复合T就能将液液二相完全分离;入口流型中二相的混合程度越高,最高分离效率越低;水相体积分数对分离效率的影响与流型相关。复合T型管分离液液二相流技术具有很好的工业应用前景。     

非线性振动下水平通道气液两相流动

将振动装置与气液两相流实验回路相结合,对非线性振动工况下水平通道内气液两相流进行实验研究。重点考察了不同振动参数对流型转换界限及摩擦压降的影响。流型图表明,非线性振动工况和稳态工况下的气液两相流动形式不同,提高振动的频率和幅度会导致流型转换界限发生改变。由实验得到的气液界面分布结果表明,振动频率对相界面波动程度有显著影响,而振动幅度则主要影响截面含气率。最后对比了非线性振动工况下的摩擦压降和经验公式的计算结果,发现两者在数值和分布上均无明显差异,说明稳态下两相流摩擦压降计算公式同样适用于非线性振动工况。     

微通道内低沸点工质流动沸腾压降特性

在压力为0.5～1.7 MPa,质量流量为381～2291 kg·m^-2·s^-1,干度为0～1.0的工况范围内试验研究微尺度通道内低沸点混合工质R32/R134a的流动沸腾压降性能,同时对两相流流型进行可视化观察。微尺度通道内径为1.92 mm,0.86 mm和0.5 mm相似文献   

Slug flow of air—water mixtures in a horizontal pipe: Determination of liquid holdup by γ-ray absorption

Two-phase pressure gradients and time-averaged values of liquid holdup have been measured for the co-current flow of air and water in a 42 mm bore horizontal pipeline. The majority of the data corresponded to the slug flow region, where rapid fluctuations in both wall pressure and holdup were observed. Instantaneous values of liquid holdup were also recorded by rapid scanning of a vertical cross-section of the pipe using the γ-ray absorption method, which enabled probability density functions (PDF) and power spectral densities (PSD) of holdup to be determined. From these functions, values of average film and slug holdups, average slug length and average slug frequency were estimated. These measurements facilitated the use of the Hubbard—Dukler slug flow model for two-phase pressure drop prediction which compared favourably with the Lockhart—Martinelli correlation over the X-parameter range 2–30.     

表面活性剂添加对气液两相流摩阻压降特性的影响

研究了表面活性剂添加对水平管内气液两相流摩阻压降特性的影响.实验中选用了环境友好的纯度为95%的十二烷基硫酸钠(SDS)作为减阻添加剂,浓度为100 mg•kg^-1.结果表明阻力减小率与流型有关,分层流型的阻力减小率可达83.3%、塞状流型和弹状流型的阻力减小率可达83.2%、环状流型的阻力减小率可达31.2%.表面活性剂可以通过改变液体物性和改变流型两个方面来影响气液两相流摩擦压降.     

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

Pneumatic conveying is an important technology for industries to transport bulk materials from one location to another. Different flow regimes have been observed in such transportation processes, but the underlying fundamentals are not clear. This article presents a three‐dimensional (3‐D) numerical study of horizontal pneumatic conveying by a combined approach of discrete element model for particles and computational fluid dynamics for gas. This particle scale, micromechanic approach is verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. It is shown that flow regimes usually encountered in horizontal pneumatic conveying, including slug flow, stratified flow, dispersed flow and transition flow between slug flow and stratified flow, and the corresponding phase diagram can be reproduced. The forces governing the behavior of particles, such as the particle–particle, particle‐fluid and particle‐wall forces, are then analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A general phase diagram in terms of these forces is proposed to describe the flow regimes in horizontal pneumatic conveying. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

基于图像多特征融合和支持向量机的气液两相流流型识别

The knowledge of flow regime is very important for quantifying the pressure drop, the stability and safety of two-phase flow systems. Based on image multi-feature fusion and support vector machine, a new method to identify flow regime in two-phase flow was presented. Firstly, gas-liquid two-phase flow images including bubbly flow, plug flow, slug flow, stratified flow, wavy flow, annular flow and mist flow were captured by digital high speed video systems in the horizontal tube. The image moment invariants and gray level co-occurrence matrix texture features were extracted using image processing techniques. To improve the performance of a multiple classifier system, the rough sets theory was used for reducing the inessential factors. Furthermore, the support vector machine was trained by using these eigenvectors to reduce the dimension as flow regime samples, and the flow regime intel-ligent identification was realized. The test results showed that image features which were reduced with the rough sets theory could excellently reflect the difference between seven typical flow regimes, and successful training the support vector machine could quickly and accurately identify seven typical flow regimes of gas-liquid two-phase flow in the horizontal tube. Image multi-feature fusion method provided a new way to identify the gas-liquid two-phase flow, and achieved higher identification ability than that of single characteristic. The overall identifica-tion accuracy was 100%, and an estimate of the image processing time was 8 ms for online flow regime identifica-tion.     

绝热状态下板壳式换热器壳侧的流型与压降

实验研究了板壳式换热器波纹通道内垂直向上气-液两相流动的流型和压降特性,讨论了圆形波纹通道内流型特征及转变机理,根据相界面形态特征将流型划分为泡状流、弹状流、膜状流和搅混流;同时分析了流型与压降之间的关系,发现泡状流中的压降波动幅值最小,弹状流与膜状流次之,搅混流中压降波动幅值最大;获得了波纹通道内单相以及气-液两相压降的分布规律,拟合了单相压降关联式,并基于Lockhart-Martinelli理论,通过分析两相摩阻系数与Martinelli参数的关系拟合了波纹通道内两相流动压降关联式,发现Chisholm参数C的值与Chisholm最初建议的光滑管内层流-层流的值接近。     

水平管稠油掺气减阻模拟实验

依托流体可视化环道装置,设计并加工稠油掺气减阻模拟装置,实验研究水平管内两种稠油模拟油掺气流动阻力特性,拍摄不同气液流量比下的管流流型,分析不同实验条件下气相对稠油的减阻效果并建立相应的压降预测模型。结果表明：在气液比0~15范围内,共观察到六种流型,分别是泡状流、弹状流、分层流、段塞流、环状流、雾状流。220^#与440^#模拟油所对应的管路减阻率分别在气液比1.17和0.96时达到最大值48.19%和33.76%,当掺气比为0.9~1.2时,减阻率均可维持在20%以上。其机理可归结为空气使油-油接触转变为油-气-油接触,降低了混合相的层间剪切应力。Dukler法不适用于高黏气液两相流,所建立的稠油-气两相压降模型预测值与实测值吻合良好,平均相对误差在20%以内。     

利用一维波和段塞稳定性模型预测分层流向段塞流的转变

利用气液二相流一维波模型和段塞稳定性模型,对直径2.54 cm水平管内空气-水二相流出现段塞流时的各相临界表观速度和临界液层高度进行了理论预测。计算中发现,2种模型分别适用于不同的流速区域,在较低的气相流速下,一维波模型的预测结果比较理想,但是在较高的气速条件下不太适合,而利用段塞稳定性模型可以较好地获得高流速下分层流向段塞流的流型转变条件。因此,结合这2种模型对发生流型转变时的临界参数作了分析,并且应用于40 mm和50 mm水平管道的油气二相流实验。将理论计算的结果和实验测得的流型数据进行了对比,并且对影响流型的管径、流速等因素作了分析,结果表明计算得到的特征参数和实验数据比较吻合。     

地形起伏管路气液两相段塞流模型研究

段塞流是气液两相流动中的一种常见流型,由于地形原因,管路多处于起伏状态,而目前国内外对起伏诱发的气液两相管路段塞流研究尚不成熟。针对实际气液两相管路中频繁出现的地形起伏段塞流,首先利用历史数据对现有段塞流模型的适用性进行了比较,建立了地形起伏状态下段塞流的液塞追踪修正模型,最后利用FLUENT软件进行了模拟,研究了管路起伏诱发状况对段塞流段塞分布、拐角处持液率、液塞长度和压降的影响,并将模拟压降与计算压降进行对比,结果表明建立的模型具有一定的精度,对于实际的地形起伏诱发段塞流管道的安全高效运行有一定的指导意义。     

水平管道油气二相段塞流稳态流动特性

使用通过自行设计并搭建的实验装置,对水平管道油气二相段塞流稳态流动特性进行了实验研究。采用压力信号互相关方法测量了段塞流平均液塞速度,通过分析得到了液塞速度、液塞长度和液塞频率随气、液相折算速度的变化规律。结果表明,当液相折算速度恒定时,随着气相折算速度的增大,液塞速度基本上呈线性增大,而液塞长度呈双曲线减小;当气相折算速度恒定时,随着液相折算速度的增大,液塞频率基本呈线性增大,而液塞长度呈双曲线减小。     

An experimental investigation of gas-liquid two-phase flow in single microchannel contactors

This paper describes two-phase flow pattern and pressure drop characteristics during the absorption of CO₂ into water in three horizontal microchannel contactors which consist of Y-type rectangular microchannels having hydraulic diameters of 667, 400 and , respectively. With the help of a high-speed photography system, flow patterns such as bubbly flow, slug flow (including two sub-regimes, Taylor flow and unstable slug flow), slug-annular flow, churn flow and annular flow were observed in these microchannels. The applicability of the currently available correlations for describing flow pattern transitions in microchannels has been examined. Generally, the predicting performance of these correlations deteriorates as the channel diameter further reduces. Toward solving this discrepancy, an empirical correlation based on the superficial Weber numbers was developed to interpret the transition from Taylor flow to unstable slug flow in three microchannels. Taylor bubble formation process in microchannels was found to be in the squeezing regime at lower superficial liquid velocities (Ca ranging from 0.0019 to 0.029) while the transition to the dripping regime was observed at the highest superficial liquid velocity of 1.0 m/s. Lengths of Taylor bubbles formed in the squeezing regime can be well represented by the scaling relation proposed by Garstecki et al. [Formation of droplets and bubbles in a microfluidic T-junction—scaling and mechanism of break-up. Lab on a Chip, 6, 437-446]. For flow patterns including slug-annular flow, annular flow and churn flow, a simple analysis based on the separated flow model has been performed in order to reveal the observed effect of the superficial liquid velocity on two-phase frictional multiplier in the present microchannels. Then, reasonable correlations for the prediction of two-phase frictional pressure drop under these flow patterns were suggested.     

对称分支并行微通道中气液两相流的均匀性规律

采用高速摄像系统研究了对称分支形并行微通道内气液两相流及弹状气泡均匀性规律。实验中分别采用含0.3% SDS的甘油-水溶液与氮气作为液相和气相。观察到弹状流和泡状流两种流型,作出了由两相操作条件构成的流型图及流型转变线。结果表明,气泡非均匀性主要由两微通道内流体之间的相互作用、下游通道中流体动力学的反馈作用以及通道制造误差造成。随液相黏度增大,气泡均匀性变好;在高液相流量以及低气相压力下操作,气泡尺寸分布更易达到均匀。基于压力降守恒原理和微通道内气液两相流阻力模型,构建了两通道中气泡尺寸的预测模型。     

水平管气液两相分层流界面剪切预测研究进展

水平管气液两相分层流虽流型简单,但由于界面存在复杂的动量和能量传递,分层流的界面剪切预测至今没有一致的结论。本文从理论模型、实验模型、数值计算3个角度出发,详细阐述水平管气液两相分层流界面剪切预测的研究现状,得出不同研究方法的优势和缺陷。针对3种研究方法,指出理论模型通过模型简化和经验关联式来建立封闭模型,实验模型则在封闭关系上修正经验关联式,但由于简化假设和实验条件的限制,使得这两种研究方法对界面剪切应力的预测具有一定的局限性;数值计算能够弥补机理模型在流场细节等方面的不足,但能够提供界面剪切预测或封闭关系的工作很少。此外,对比了5种不同形式的已有模型对气液两相分层流持液率和压降预测的结果。最后展望了水平管气液两相分层流界面剪切预测的研究趋势,提出理论和实验研究需要提出更详细的局部模型,并考虑工程实际工况进行研究,发展针对气液界面计算的新方法,并为分层流提供封闭关系则是数值计算研究面临的挑战。     

高宽比对矩形通道内蒸汽冷凝传热特性及流型影响的研究

通过可视化流型观测及实验测量,研究了单边换热矩形小通道的高宽比对两相流型、平均冷凝传热系数及两相流动阻力的影响,采用高速摄像机拍摄了环状流、环波状流、波状流、弹状流、塞状流及泡状流6种典型流型。研究表明,高宽比为1：2及1：3的通道内出现流型种类较为全面,而在高宽比为1：5通道内基本无弹状流、塞状流及泡状流。1：5通道内环状流所占区域较1：2及1：3通道大,随入口蒸汽质量流速的增加,差值逐步减小。随着通道高宽比的减小,平均冷凝传热系数逐渐增大;不同高宽比通道中平均冷凝传热系数间的差值随入口蒸汽质量流速的增加而减小;蒸汽质量流速足够高时,高宽比对传热系数基本无影响。通道内两相流压降随通道高宽比的减小而增大;随着入口蒸汽质量流速的增加,不同比例通道内的两相流动压降差距逐渐增大。     

复合T形管对气液两相流的分离

在诸如天然气、化工、冶金、电力等许多工业过程中广泛存在气液两相流,传统上采用分离罐或旋风分离器等分离两相流,不仅设备成本高、易泄漏,而且维护保养和更新都不方便。T形管分离器具有结构简单、集约、经济、安全、维修更新方便等优点,但缺点是简单T形管的分离效率较低,新型复合T形管是对简单T形管的一种改进,期望能提高两相的分离效率。以空气一水为两相流工作介质,用主管水平侧支管垂直向上的简单T形管和复合T形管作为两相流动的分离器,在层状流和塞状流条件下进行两相流分离实验。结果表明,无论在层状流还是在塞状流条件下,复合T形管气液两相的分离效率都比简单T形管有了显著的提高,增加复合T形管的连接管数,能进一步提高分离效率,一般在层状流时连接管数为5管以上的复合T能完全分离气液两相;而流型进入混合程度较高的塞状流时,采用连接管为5管以上的复合T也能完全分离气液两相流;相同流型下,增加气体或液体的流速,对复合T形管分离效果不利,最大分离效率下降。     

水平管气液两相段塞流的波动特性

气液两相段塞流是液塞和长气泡在空间和时间上的交替,在流动过程中表现出间歇性和不稳定性。系统地研究了水平管中段塞流持液率、压力和压差的波动特性。结果表明,段塞流持液率的概率密度分布为双峰分布,高持液率峰对应于液塞区,低持液率峰对应于液膜区;在压力的概率密度分布中,当压力测试点到管道出口之间的段塞单元数目少时,压力分布出现双峰分布;当压力测试点到管道出口之间的段塞单元数目多时,压力分布出现单峰分布;压差信号分布呈单峰分布。这些特征为流型识别提供了可靠的段塞流标识。