卧底管-悬链线立管严重段塞流数值模拟

POT深海油气田投产前优选并构建了卧底管-悬链线立管集输系统,严重段塞流的预防及影响因素分析至关重要。该文基于卧底管-悬链线立管结构参数及生产参数设计,应用OLGA软件对管线内的流动进行数值模拟,计算分析产量和气液比等生产参数对流型的影响,预测严重段塞流并描绘严重段塞流的流型特征,监测不同产量及气液比情况下立管内最大液塞长度及立管底部最大压力波动值。计算结果表明,卧底管-悬链线立管结构参数设计合理,设计的生产参数范围内不会产生严重段塞流,而在低产量情况下严重段塞流特征规律明显。计算分析产量及气液比与流型的关系,绘制了严重段塞流流型区间预测图。计算得出立管内最大液塞长度及立管底部最大压力波动值,着重分析节流法在抑制严重段塞流中的效果,得到节流阀开度为0.2的POT深海油气田最优化结果,为严重段塞流的预防提供依据。     

管径对垂直上升管内气液两相流流型的影响

以空气和水作为介质,在管径分别为20mm与8mm的垂直上升管内进行了常压下气液两相流流型的实验研究,得到了这两种管径下泡状流、弹状流、乳状流和环状流等流型,得到的绝大部分实验点与Hewitt和Roberts流型图相符合,并根据实验结果修正了流型图的转化边界.对于气液两相流垂直上升流动,环状流发生所需的气相折算速度几乎不随液相折算速度的变化而变化.不同管径条件下,各种气液两相流流型发生的范围和转换趋势基本一致,乳状流向环状流的转换界限基本重叠,而泡状流与弹状流的界限变化大一些.由于弹状流的换热与泡状流的换热完全相同,因此泡状流与弹状流的界限误差对传热而言并不重要,可以忽略管径对Hewitt和Roberts流型图的影响.     

以叶轮起旋的气液两相螺旋流摩擦阻力特性实验研究

该文对以叶轮起旋的水平管内气液两相螺旋流的摩擦阻力压降特性进行了实验研究,水平实验管段为内径23 mm,长度为2 m的有机玻璃管,实验工质为空气和水,气相折算速度为0 m/s–3 m/s,液相折算速度为0 m/s–1.5 m/s。主要研究了流速以及叶轮参数对压降的影响,对比分析了气液两相非旋流与气液两相螺旋流的压降特点,实验结果表明:流体流速是管内摩擦阻力特性的重要影响因素,随着气相折算速度的增大,管内压降逐渐增大。叶轮参数对压降亦有较大影响,随着起旋角度的增大或者随着叶片面积的减小,压降均有逐渐变大的趋势。与气液两相非旋流相比,气液两相螺旋流的压降进一步增大;且随着气相折算流速的增加,螺旋流的压降增大速度要高于非旋流。最后,基于Lockhart和Martinelli方法,根据实验数据建立了气液两相螺旋流压降计算模型,研究结果表明理论值与实验测量值吻合较好。     

竖直较大管径内气液两相流截面含气率实验研究

截面含气率是气液两相流动过程中的关键参数之一.在大管径流道内的气液两相流,弹状流难以形成,与常规通道相比,其流型特征明显不同.适用于常规通道截面含气率的一般计算方法,对于大管径流道而言,其适用性也较差.本文通过研究较大直径圆管内的气液两相流动过程,寻找适合于过渡尺寸流道内两相流动截面含气率的计算方法,从而建立起完整的、针对各个尺度范围内截面含气率的计算方法.实验选圆管直径为50 mm,介于常规通道和大通道之间;以空气和水作为工质,气相、液相折算速度的范围分别为0.05-2.0 m/s及0.01-2.0 m/s.首先利用获得的截面含气率实验数据,对适用于常规通道和大通道的截面含气率计算模型进行了评价;然后通过分析几类漂移流模型计算方法的分布系数和漂移速度的变化规律,解释了Hibiki-Ishii、Kataoka-Ishii、Kawanishi等几个模型计算误差较大的原因.     

卧底管-立管系统严重段塞流瞬态数值模拟

该文对卧底管系统采用分层流理论模型,立管系统采用分相流理论模型,考虑立管内摩擦压降,结合漂移流速度模型,对初始条件提出一种不需要经验模型的方法,建立了卧底管-立管系统气液严重段塞流的一维瞬态理论模型。对下倾管-垂直立管/悬链线立管两类系统,将数值模拟结果与文献中的实验结果进行对比,研究表明该理论模型对严重段塞流周期和压力波动幅值的数值模拟结果与实验结果吻合良好,而且能够成功地模拟实验中发现的四类流型。在此基础上,利用理论模型进一步对严重段塞流压力波动与周期,立管内气液流体速度、含气率及质量分布特性等进行了数值模拟分析,获得了这些流动参数的变化规律。     

水平分支管路中油水两相流动研究

该文研究了两种直径的直管油水两相流动对流型和相含率的影响和在不同管径的水平并行分支管路中的相含率变化规律.实验设备包括内径为50 mm的水平主管道和内径为25 mm的分支管路.得到了不同入口条件下实验管段的流型和相含率图.实验指出:管道的尺度变化对于流型的影响较小,但对于油水两相的相含率和速度滑移有显著的作用.当油水两相流在并行分支管路中同时流动时,随着入口处水的表观流速增大,并行主管的截面油含率与并行分支管的差距逐渐缩小.     

垂直管道内油-水两相环状流的流动特征

该文通过实验研究了垂直上升和垂直下降管道内油水两相混合液的流动特征。实验段管道的内径为25 mm,垂直段长度为1500 mm。为了得到油水两相环状流流型,分别在垂直管道的入口和出口处安装有收缩和扩张管道。实验中的油相为白油(97 mPa·s,860 kg/m3),水为普通生活用水(1 mPa·s,998 kg/m3),含油率范围为0–100%,混合速度为0.28 m/s–4.65 m/s。研究中,分别采用压力传感器、高速摄像机和快关阀对管道中两相流动的压降、流型和含油率等特征进行了测量和记录,并采用两流体理论模型对流动中的摩擦压降进行预测。研究结果显示:流动中形成的水包裹油的广义环状流型,可以很好的降低摩擦压降,并可以将摩擦压降分为壁面摩擦和界面摩擦两部分,采用两流体理论对压降梯度进行预测,误差小于20%;由于油水两相间的密度差和截面相分布特征,使两相之间存在速度滑移,可以看出垂直上升和下降管道内的油相的相速度值均高于水相,在含油率为60%–80%时其差值达到最大。     

鼓泡塔内气液两相流动力特性数值模拟研究

利用CFD软件模拟的方法研究鼓泡塔内气液两相流动力特性,为鼓泡塔的设计提供依据。采用欧拉-欧拉双流体模型分别结合标准k-ε紊流模型和RNG k-ε紊流模型对鼓泡塔内气液两相流进行数值模拟,并使用Phase Coupled SIMPLE算法进行速度与压力耦合求解。比较鼓泡塔内轴截面(y=0)处不同高度液相速度和气相速度的变化情况,发现速度沿径向呈现出抛物线分布,沿水深方向越接近通气孔,速度越大,且气相速度整体大于液相速度。通过将z=0.28 m处的垂向液相速度与实验值比较,得出欧拉-欧拉双流体模型结合标准k-ε紊流模型模拟鼓泡塔气液两相流动力特性优于RNG k-ε模型,且发现上升力对模拟结果有显著的影响。     

曝气池中气液两相流速度场分布的实验研究与数值模拟

气液两相流广泛存在于水利工程、废水处理等领域,其在气液装置中的流型流态及速度场分布可直接影响装置运行效能。本文采用实验研究与数值模拟相结合的方法,对圆柱形气液装置进行PIV实验,获得了准确的气液两相流气相速度场分布;在充分考虑湍流、曳力、升力、湍流分散力等作用下,采用欧拉-欧拉双流体模型和气泡群平衡模型对气液两相流流场进行了数值模拟,并将模拟结果与实验结果进行验证,所得结果误差控制在10%左右。结果表明,本文提出的模拟方法在气液两相流模拟中能够得到较准确的两相流动规律和速度场分布情况。     

有限变形下固流多相介质耦合问题的数学模型及失稳条件

本研究以多相连续介质力学理论为基础，把多相连续介质抽象为叠合连续体，考虑了固相骨架的有限变形、液相及气相之间的相互作用，建立了固-液-气三相介质相互耦合变形力学的基本理论和数学模型，提出了固相骨架有限变形下三相耦合介质的失稳条件．有限变形下失稳的临界条件对应着固相骨架的总刚矩阵奇异，为多相介质力学问题的数值模拟提供了理论基础．     

Experimental study of flow patterns and pressure drops of heavy oil-water-gas vertical flow

A stainless steel apparatus of 18.5 m high and 0.05 m in inner diameter is developed, with the heavy oil from Lukeqin Xinjiang oil field as the test medium, to carry out the orthogonal experiments for the interactions between heavy oil-water and heavy oil-water-gas. With the aid of observation windows, the pressure drop signal can be collected and the general multiple flow patterns of heavy oil-water-gas can be observed, including the bubble, slug, churn and annular ones. Compared with the conventional oil, the bubble flows are identified in three specific flow patterns which are the dispersed bubble (DB), the bubble gas-bubble heavy oil, and the bubble gas-intermittent heavy oil (B_g – I_o). The slug flows are identified in two specific flow patterns which are the intermittent gas-bubble heavy oil (I_g – B_o) and the intermittent gas-intermittent heavy oil (I_g – I_o). Compared with the observations in the heavy oil-water experiment, it is found that the conventional models can not accurately predict the pressure gradient. And it is not water but heavy oil and water mixed phase that is in contact with the tube wall. So, based on the principle of the energy conservation and the kinematic wave theory, a new method is proposed to calculate the frictional pressure gradient. Furthermore, with the new friction gradient calculation method and a due consideration of the flow characteristics of the heavy oil-water-gas high speed flow, a new model is built to predict the heavy oil-water-gas pressure gradient. The predictions are compared with the experiment data and the field data. The accuracy of the predictions shows the rationality and the applicability of the new model.     

Prediction of oil-water flow patterns,radial distribution of volume fraction,pressure and velocity during separated flows in horizontal pipe

Flow of two immiscible fluids gives rise to variety of flow patterns,which influence transportation process.In this work,we present detailed analysis on the prediction of flow pattern maps and radial distribution of volume fraction,pressure and velocity of a pair of immiscible liquids through a horizontal pipeline by computational fluid dynamics(CFD) simulation using ANSYS FLUENT 6.3.Moderately viscous oil and water have been taken as the fluid pair for study.Volume of fluid(VOF) method has been employed to predict various flow patterns by assuming unsteady flow,immiscible liquid pair,constant liquid properties,and co-axial flow.From the grid independent study,we have selected 47 037 number of quadrilateral mesh elements for the entire geometry.Simulation successfully predicts almost all the flow patterns(viz.,plug,slug,stratified wavy,stratified mixed and annular),except dispersion of oil in water and dispersion of water in oil.The simulated results are validated with experimental results of oil volume fraction and flow pattern map.Radial distribution of volume fraction,pressure and velocity profiles describe the nature of the stratified wavy,stratified mixed and annular flow pattern.These profiles help to developing the phenomenological correlations of interfacial characteristics in two-phase flow.     

均质多孔介质中纳米颗粒吸附层的水流滑移模型

考虑纳米颗粒吸附边界层对管径大小的影响和不同流态时的岩心渗透率的差异,建立了基于纳米颗粒吸附的均质多孔介质水流滑移数学模型(K-L MⅡ)。测试了油基和水基两种纳米流体的减阻效果,两组岩心水相渗透率的增幅平均分别为46.5%和76%。利用K-L MⅡ和K-L MⅠ计算了两组岩心中的水流滑移长度,大约在20–80 nm左右。结果显示,两者的差异较大,最大相差100%,表明不宜用K-L MⅠ计算具有吸附层厚度影响的滑移长度。利用K-L MⅡ解释了纳米颗粒吸附造成孔道减小而注水量增加的矛盾,为阐述纳米减阻机理提供了理论依据。K-L MⅡ也适用于吸附层厚度为0的水流滑移效应,具有普适性。     

A MODEL FOR LIQUID SLUG LENGTH DISTRIBUTION IN VERTICAL GAS-LIQUID SLUG FLOW

The slug length and the trailing Taylor bubble velocity in an upward vertical slug flow were measured by using the optical probes and the EKTAPRO 1000 high speed motion analyzer. The correlation between the trailing bubble velocity and the length of liquid slug ahead of that bubble is derived from the experimental data. Based on this correlation as well as the bubble overtaking mechanism, a model for the slug length distribution at any designated locations along the pipe is proposed. The predicted results are in agreement with the experimental data.     

润湿性微纳米圆管中去离子水的流动特征

在传统的流体力学中,流体在固壁处流速为零,即无滑移边界条件。在微纳米条件下,由于固液界面作用力增大,无滑移边界条件不再适用。该文首先从微米石英圆管中的流动实验现象出发,给出润湿性边界黏滞层厚度随应力变化的边界模型。在此基础上推导出层流条件下,微纳米管中的流量公式,并对流量公式进行渐近分析,同时也分析流动微纳米尺度下的流动特征。最后用微米圆管中去离子水的流动实验,对新建的理论模型进行验证。研究表明:润湿性条件下,边界黏滞层厚度随驱动力的增大而减小;新建立的微纳米尺度下的边界模型和流量公式非常符合实验结果,其中一次方的流量模型应用时更为简单,在压力梯度较小时,指数项起作用产生了非线性流动的效果。     

EXPERIMENTAL AND NUMERICAL INVESTIGATIONS ON HORIZONTAL OIL-GAS FLOW

Experiments were carried out to investigate the characteristics of oil-gas flow in a horizontal pipe on a large scale (with the inner diameter D = 125 mm). With the experimental data, the flow patterns were presented. Through the analyses for the flow regime transition, it was found that there was a critical superficial velocity of liquid phase for the flow regime transiting from stratified flow to slug flow. The slug flow could not occur until the superficial velocity of liquid phase was higher than the critical velocity. For the flow pattern transiting from stratified to slug flow, the transmitting velocity of gas phase decreases with the augmentation of superficial velocity of liquid phase. On the basis of the experiments, numerical simulations of different flow patterns and their transitions were performed with the use of the Volume Of Fluid (VOF) technique. The results of the computations are shown to match well with the measured data in the experiments.     

气液两相水平管流分层--段塞流型转换机制研究

本文根据Stokes溃坝理论 ,提出了一个新的物理模型。通过对段塞单元的稳定性进行分析得出段塞保持稳定的临界液面高度值 ,从而得出分层流向段塞流转换的条件 ,并分析了液体粘度、管径大小对流型转换条件的影响。计算结果与实验值较为吻合     

折流式厌氧反应器水力特性分析

折流式厌氧反应器(ABR)的处理效果受水力特性的影响较大,而水力停留时间(HRT)又是影响反应器内水力特性的一个重要因素。运用欧拉双流体模型和标准k-ε紊流模型,对不同HRT下ABR反应器内的多相流流场进行三维数值模拟,并从反应器内水流速度、固含率两个方面探讨分析了HRT对反应器内部流场特性的影响。分析结果表明:HRT变化对各反应室内降流区水流速度的影响不大,升流区内的循环水流速度随HRT的减小而增大;反应器内污泥颗粒的分布范围受HRT影响显著,HRT过短或过长,均不利于提高反应器的处理效率,5~8 h时为ABR反应器的最佳水力停留时间,最有利于去除污废水中的污染物。     

井筒环雾流传热模型及其在深水气井水合物生成风险分析中的应用

该文采用Hewitt流型判别法,表明深水含水气井测试时井筒内多为环雾流,考虑了气核与液膜间速度及热力学性质差异,建立了环雾流传热模型,与南海某深水气井实测数据对比,模型预测误差在5%以内。计算表明,忽略含水影响的气体单相模型在含水量大于0.1%时,泥线以上井筒压力和温度预测误差均超过10%,应用该研究建立的环雾流模型则可以得到更准确的结果。含水会使泥线以上一定范围内井段井筒温度显著降低,压力损失增大。产气量较低时,含水量对水合物生成风险基本无影响;产气量较高时,含水量会使得水合物生成区域下界下移,水合物生成区域增大,并使过冷度增大,更容易诱导水合物生成,水合物生成风险增大,需要增加水合物抑制剂用量,并加深注入位置。产水会使无水合物生成所对应的临界产气量增大,需要调整水合物抑制剂用量和注入位置。     

A PHYSICAL MODEL FOR PREDICTING THE PRESSURE DROP OF GAS-LIQUID SLUG FLOW IN HORIZONTAL PIPES

A comprehensive treatment of all sources of pressure drop within intermittent gas-liquid flow is presented. A slug unit is divided into three parts and the pressure gradient of each part is calculated separately. In the mixing zone the momentum theory is employed and the mixing process between the film and slug is simulated by a two-dimensional wall jet entering a large reservoir to calculate the mixing length. The boundary layer theory is utilized to calculate the pressure drop for the slug body and the momentum equation of the film zone is integrated to calculate the pressure drop for the film zone. The pressure drop predicted in present model is in good agreement with all the measurements.