湿气管道积液临界气速预测的新模型

气田开发经常采用湿气集输方案。针对湿气输送管道出现的积液问题,基于分层流最小界面剪切应力准则,利用气液平界面分层流液膜区的速度分布规律,建立了求解积液临界气速的新机理模型。由分层流液膜区的流场描述和气相动量方程得到气液界面剪切应力的表达式;利用界面剪切应力函数曲线特性,可以通过界面剪切应力关于持液率求导获得临界气速。以不同文献中收集的临界气速实验数据,对新模型和其他具有代表性的湿气管道积液模型进行验证对比,表明新模型的预测精度要优于其他模型。     

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。     

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。     

倾斜圆管内气液两相分层流界面的稳定性分析

<正>l 弓l言 气液两相流分层流界面波特性及界面稳定性分析对理论和应用具有重要意义.50年代,Banjamin”’、Miles”’和 Hanratty’‘’“开始了此方面的研究.以往研究中,均采用 Jeffreys”’的方法,即利用液相动量方程的积分形式,气相的影响只作为液相动量方程的边界条件.另外也有研究者从N-S方程出发,通过对实际问题的适当简化以研究界面稳定性”‘. 本文利用双流体模型研究了倾斜圆管内气液两相分层流的界面稳定性,系统研究了管道几何条件及流动状况对稳定性的影响.2 数学模型 对如图1所示的倾斜管内分层流,假定两相间不存在热量传递和相变过程,其一维双流体流动模型为”-“ ～r 入八人）乃t十别八U。人）/肚一0（I） ltw 8（pkA。U。）/9 t + 3（pkA。厂。ZtZ）/sx 、_/.\—一,。J。士。/;+八。A。slip J>>一二卜 卜。二.t 一洪人八）/gx+AdA/a工（2） 一人二二>二v抑Q厂二厂了 式（1）、式（2）中k—l或g,当k—g时,取 pry——“一”号,k—l时贩“十”号.素流速度分布均 匀,厂。一 l“’‘;层流根据液膜内速度分布可知, 图 1 分层流示意图——”———一’—””—””——～ 八一4/3““二 气液两相静压项用文献〔幻的方 F。Ic0d屯＊r＊donof盯r＊1m叨n0w”‘’-’“‘一‘””—’““——一‘一     

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimented data are presented for the void fraction aud the shear stresses of stratified gas-liquid flow in a pipe, A new technique was used to measure the interface shear strew. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress prone at the gas-liquld interface. A new formula ,relatiog to the interfacial friction factor with the void fraction and superficiol gas Rcynold number, was dewloped to predict the interface shear stress. The predicted values are in good agreement with experimental data.     

BASIC EQUATION OF TURBULENCE AND MODELING OF INTERFACIAL TRANSFER TERMS IN GAS-LIQUID TWO-PHASE FLOW

Turbulence is one of the most important phenomena in analyzing thermohydrodynamic characteristics of gas-liquid two-phase flow. For the purpose of accurate prediction of the turbulence phenomena, a basic conservation equation of Reynolds stress was derived based on the local instant formulation of mass and momentum conservations of two-phase flow. In this equation, interfacial transfer terms of turbulence appear as source terms. Detailed considerations on these transport terms were carried out. It was shown that they consist of a viscous damping term due to small scale interfacial structures, a drag induced turbulence generation term due to large scale interfacial structures and a term representing the exchange between surface energy and turbulence. Based on the mechanistic modeling and turbulence modulations, carried out were physical interpretations of interfacial area concentrations of small and large scale interfacial structures, a viscous damping term due to small scale interface and turbulence generation term due to large scale interface.     

气-液两相降膜流动及传质过程的CFD研究

利用VOF法建立了考虑表面张力动量源项、气液相间摩擦力动量源项以及相问传质源项的CFD计算模型,定量描述了气．液两相逆流降膜传质过程。根据CFD模型,计算了不同液相进口浓度和不同气相流量条件下,异丙醇稀溶液的解吸过程,模拟得到的液相出口浓度与实验数据吻合很好。相界面处的浓度分布表明。随自由表面波动,界面浓度会发生剧烈脉动。液相总传质系数增强因子R的实验值与CFD模拟均表明,即使在很小的传质推动力下R也大于1。由于CFD模型不考虑Rayleigh-Benard-Maragoni效应,则这种现象,可解释为界面波动对传质增强的结果。这也证明增强界面波动是一种强化传质分离过程的有效途径。     

湿天然气在上倾管道的气液两相流动特性研究

利用VOF (Volume of Fluid)模型模拟了湿天然气在上倾管道的气液两相流动特性。讨论了管道内气体入口流速对气液两相流动特性的影响。结果表明,当管道内气体入口流速较低时,由于气液界面的切应力小于液相在上倾段的重力分力,因此气体无法将液体携带至管道上倾段。随着气速的增加,气液界面的切应力逐渐增大,气液界面开始出现波纹,气体逐渐将液体携带并完全平铺于管道上倾段。     

Pressure drop and bubble-liquid interfacial shear stress in a modified gas non-Newtonian liquid downflow bubble column

A functional form of equation for predicting pressure drop in a modified non-Newtonian downflow bubble column has been formulated. The equation has been developed based on the bubble formation, drag at interface and the wettability effect of the liquid. Also the bubble-liquid interfacial shear stress in two-phase flow is analyzed and correlated with the dynamic, geometric and physical variables. The functional form of equation appears to predict the pressure drop satisfactorily for two-phase dispersed flow in the co-current modified downflow bubble column with carboxy methyl cellulose (CMC) solution in water with different concentrations.     

Interfacial friction factor determination using CFD simulations in a horizontal stratified two-phase flow

Stratified two-phase gas–liquid flow in three-dimensional (3D) is challenging because of the difficulty in determining the shear stresses at the walls and at the gas–liquid interface. The study is simplified by considering only the gas and the gas–liquid interface. The gas flows between the fixed wall of the pipe and the interface, which is regarded as wall moving at liquid velocity. It is shown, using a CFD code, that one can determine the correct horizontal and vertical profiles of the longitudinal velocity of the gas. Seven experiments done by Strand (1993) for a horizontal stratified gas–liquid flow are simulated. The simulation results are compared with experimental results, and also to the numerical results of Meknassi et al. (2000). We deduce from these comparisons that the approach suggested in this work is very valuable. Then expressions for calculating the gas–wall friction factor, and the gas–liquid interface friction factor are presented. These factors are crucial for evaluating the shear stresses. It appears, after comparison with the experimental values that the correlation proposed for calculating the friction factor at the interface, in the present work, agree with the experimental values better than that given by Taitel and Duckler, 1976a, Taitel and Dukler, 1976b.     

绝热层流泡状流运动的双流体模型

绝热层流泡状流是泡状流研究中的一个基础范例 .目前描述绝热层流泡状流常采用的双流体模型由于相间作用考虑欠缺而适用性差 .本文结合理论和实验研究结果导出了描述壁面“排斥”作用的表达式 ,并建立了一个封闭的双流体模型 .模型预测值和实验值的比较表明 ,由于相间作用的合理考虑 ,扩大了该模型的适用范围     

竖直管外气液逆流环状降膜速度与温度分布

建立了竖直管外环状降膜气液逆流传热传质条件下稳态层流降膜一维速度分布和二维温度分布模型,以及膜厚和降膜表面热通量的数值计算方法。表面热通量的模型计算值与实验值在气体Reynolds数Re_g<1200的范围内吻合较好,表明基于界面摩擦因子求解模型的方法在两相均为层流条件下是可靠的。模型显示了降膜速度分布和温度分布的非线性特征,降膜表面附近陡降的温度梯度表明,减小膜厚是强化降膜传热传质过程的有效途径。     

Drag reduction in cocurrent horizontal natural gas-hexane pipe flow

Drag reduction in two-phase cocurrent horizontal natural gas-hexane pipe flow was studied experimentally. The effects of pipe diameter, gas flow rate, liquid flow rate, and additive concentration were investigated using the Dowell APE drag reducer. In the annular-mist flow regime studied, it was found that drag reduction increased with decreasing gas rate for a given liquid rate, drag reduction decreased with increasing friction velocity and it decreased with decreasing gas-liquid ratio for a given friction velocity. Although the drag reduction decreased rapidly as the liquid-gas ratio approached zero, drag reductions as high as 34 percent were obtained. Attempts to predict two-phase drag reduction were unsuccessful as it was found to depend upon friction velocity, liquid and gas rates, liquid-gas rate ratio, pipe diameter and additive concentration.     

Numerical simulation of churn flow in a vertical pipe

A numerical simulation of the churn flow regime of air-water and R134a vapour-liquid mixtures by means of the volume of fluid (VOF) method is presented. The focus of the paper is on the inlet region of a vertical pipe. An axisymmetrical domain is used, reproducing the region next to the porous wall liquid injector of a typical test section for the investigation of vertical gas-liquid flows.A simplified model of the levitation process of the ring-type waves typical in churn flow is proposed. The influence of the gas Froude number on the waves amplitude is shown by means of the simplified model and used to explain the numerical results.A comparison of the numerical results with experimental wave frequency data and visualizations available in the literature is performed. The velocity field in the forming wave region and the pressure and shear stress variations along the interface are shown.Simulations have been performed at different liquid and gas superficial velocities and pipe diameters and the influence of these parameters on the gas-liquid interface is discussed.     

基于段塞流捕捉的高黏油气两相流模型的建立与验证

随着传统油田的快速消耗,高黏稠油的开发逐渐引起了重视。有关高黏油的气液两相流研究主要集中在国外,国内的相关研究目前还较少。本文针对高黏油气混输管路,建立了一种捕捉段塞流的形成和发展过程,并进行两相流水力计算和液塞长度统计的组合模型。通过气液相间滑移速度和液相连续性方程的求解得到管路中不同时刻和位置的持液率,以持液率的变化反映段塞的形成和发展。建立气液动量守恒方程关联持液率和压力,得到管路中各位置的压力变化。闭合关系式中,通过液塞平移速度、壁面及气液相界面的剪切力关系式加入黏度的影响,最终建立适用于高黏油气两相流的段塞捕捉模型。使用不同来源的数据验证模型计算压降和液塞长度的准确性,数据分别来源于国外研究者的实验数据和大庆油田的现场数据。结果表明,模型具有较高的计算精度,大部分压降误差在±15%以内,大部分液塞长度误差在±20%以内。     

新型外分液结构调控水平管间歇流流型

相变传热广泛存在于换热领域,而两相流中的厚液膜是恶化相变传热的根本原因。提出在换热管壁面设计新型网状外分液结构,利用金属网进行间歇流气液非能动相分离,从而调控流型、强化传热。通过搭建空气-水水平管冷态实验台,证实当间歇流经过外分液结构时,气体在表面张力作用下被金属网孔拦截,液桥和厚液膜则被分离出换热管,使管内液相减少,气相汇聚,有效增大气相与管壁的接触概率;多级分液后气液两相长度比呈振荡上升,甚至将间歇流调控为分层流。减小液速或增大气速,分液效果越好,间歇流最终转变为分层流所需经历的外分液级数越少,预期此结构可显著提高相变传热效果。     

A multidimensional model for annular gas-liquid flow

A finite volume method-based CFD model has been developed to simulate steady, turbulent, two-dimensional annular gas-liquid flow in a duct. The gas flow is treated as being equivalent to flow through a rough-walled duct. The effect of the liquid film on the gas phase is included in the form of modified wall functions which incorporate the well-known triangular relationship (Annular Two-Phase Flow, Pergamon Press, Oxford, 1970) that exists among wall shear stress, film flow rate and film thickness in annular flow. The presence of droplets is accounted for by solving an additional scalar transport equation for the mass fraction of the droplets. Entrainment and deposition of droplets are included as source term and boundary condition, respectively, in the mass fraction equation. It is shown that the resulting model, while retaining simplicity of formulation, gives good predictions of the literature data of annular flow parameters under equilibrium and non-equilibrium conditions.     

气升式陶瓷膜过滤过程的气液两相流模拟

采用VOF双流体模型对19通道气升式陶瓷膜过滤装置进行气液两相流的流体动力学模拟,研究了曝气孔直径和曝气量对气升式陶瓷膜过滤装置的气含率、环流液速、膜面剪切力及膜管内湍流强度的影响,模拟结果与实验结果的误差在5%~10%之间。结果表明,气升管与降液管的气含率都随曝气量增大而增大,随曝气孔直径减小而增大;环流液速、膜面剪切力及膜管内的湍流强度都随曝气量增大先增大,当曝气量达到400L·h^-1时其增大趋势变缓。通过实验和模拟比较了3种不同孔径的曝气头,环流液速与曝气孔的直径关系不大,仅与曝气量相关,但曝气孔直径越小,其膜面剪切力越大,越有利于过滤过程的进行。     

THE TAYLOR PUMP: VISCOUS-FREE SURFACE FLOW DRIVEN BY ELECTRIC SHEAR STRESS

The pump invented by G.I. Taylor consists of low conductivity liquid in an insulated tank with electrodes at each end, one of which has an extension canted over the liquid/gas interface. When a potential difference is imposed between the electrodes, an electric shear stress acts on the interface and drives a Marangoni-like flow. The steady, two-dimensional flow of an incompressible, Newtonian, ohmic liquid in the tank is analyzed by solving simultaneously the Navier-Stokes equations for velocity and pressure in the tank and the Laplace equation for electric field in the liquid and the gas. The results show that an egg-shaped vortex develops in the liquid as the relative importance of inertial to viscous forces increases, in accordance with the experiments of Melcher and Taylor (1969). The methods developed here can be readily extended to analyze drop deformation and enhancement of mass transfer in two-phase systems due to an imposed electric field.