Investigation on the performance of a helico-axial multiphase pump under slug flow

The helico-axial multiphase pump is often used for gas-liquid mixture transportation in offshore oilfields,and slug flow is the main reason for the unstable operation of the pump.Aimed for slug flow condition,a self-designed three-stage multiphase pump is set to the object to perform unsteady simulations and fluid-structure interaction calculations,and the inlet gas void fraction(IGVF)is set from 20%to 80%.The results show that affected by the flow from the slug,the gas-liquid two-phase flow pattern in the multiphase pump changes sharply,resulting in severe fluctuations in the differential pressure,spindle torque and deformation of the multiphase pump.The gas-phase enters the first-impeller along the suction blade surface when affected by Taylor bubbles,while the second and third-stage impellers gas-phases are in the form of small air masses flow into the impeller along the pressure blade surface.The deformation trend of impeller torque,differential pressure and the main pump spindle is similar to that of trigonometric function,while the fluctuation of torque is more intense,and the shape variable of spindle increases with the inflow of liquid plug,and the maximum deformation amount increases by10.9%at high GVF relative to IGVF.

Gas-liquid-liquid slug flow and mass transfer in hydrophilic and hydrophobic microreactors

Gas-liquid-liquid three-phase slug flow was generated in both hydrophilic and hydrophobic microreactors with double T-junctions.The bubble-droplet relative movement and the local mass transfer within the continuous slug and the dispersed droplet were investigated.It was found that bubbles moved faster than droplets under low capillary number(Ca),while droplets moved faster upon the increase of Ca due to the increased inertia.For the first time,we observed that the increased viscosity of droplets fastened the droplet movement.The mass transfer in the continuous slug was dominated by convection,leading to nearly constant global mass transfer coefficient(k_(L)a);while that in the dispersed droplet was dominated by diffusion,resulting in k_(L) decreasing along the channel.Such features are analogical to the corresponding gas-liquid or liquid-liquid two-phase slug flow,but the formation of bubble-droplet clusters caused by relative movement lowered the absolute mass transfer coefficient.These results provide insights for the precise manipulation of gas-liquid-liquid slug flow in microreactors towards process optimization.

Research on bubble trajectory and flow structure in helical-axial multiphase pump

The oil-gas two-phase hybrid transportation technology is one of the innovative technology directions for the exploitation and transportation of marginal and deep ocean oilfields.The helical-axial multiphase pump is a key equipment for oil and gas extraction.At this stage,most of the research on this kind of pump focuses on the improvement of the structure and conveying performance.However,because of insufficient understanding of the flow behavior and mechanism of bubbles,it is easy to cause the gas-liquid separation.In this paper,the numerical simulation and test are combined to explore the changes in the bubble trajectory and flow structure of the helical-axial multiphase pump.The results shown that when the speed is lower than 1200 r/min,the bubble reaches the maximum volume at 1/2 of the midline of the impeller blade and it contact with the pressure surface,broken to the suction surface.When the rotation speed is higher than 1450 r/min,the number of bubbles in the impeller increases and the size decreases.The backflow occurs in the tip clearance and strength increases continuously.The research results have important significance for the theoretical design and engineering application of the helical-axial multiphase pump.

The 3D Modeling of Blades of Multiphase Flow Helico-Axial Pump's Rotor Based on Solidworks

The structure of multiphase flow helico-axial pump＇s rotor and how to model the rotor, especially the blades of the rotor, based on the Solidworks software. More important, the principle of the blade design is mainly introduced. Under the guide of the principle, the 3D coordinates of the blade data points can be got by matlab programming. In the paper, the design step and the modeling step are particularly described through a concrete example.

Flow Pattern and Pressure Fluctuation of Severe Slugging in Pipeline-riser System

During the exploitation of offshore oil and gas,it is easy to form severe slugging which can cause great harm in the riser connecting wellheads and offshore platform preprocessing system.The flow pattern and pressure fluctuation of severe slugging were studied in an experimental simulation system with inner diameter of 0.051 m.It is found that severe slugging can be divided into three severe slugging regimes：regime I at low gas and liquid flow rates with large pressure fluctuation,intermittent flow of liquid and gas in the riser,and apparent cutoff of liquid phase,regime II at high gas flow rate with non-periodic fluctuation and discontinuous liquid outflow and no gas cutoff,regime III at high liquid flow rate with degenerative pressure fluctuation in form of relatively stable bubbly or plug flow.The results indicate that severe slugging still occurs when the declination angle of pipeline is 0,and there are mainly two kinds of regimes：regime I and regime II.As the angle increases,the formation ranges of regime I and regime III increase slightly while that of regime II is not affected.With the increase of gas superficial velocity and liquid superficial velocity,the pressure fluctuation at the bottom of riser increases initially and then decreases.The maximum value of pressure fluctuation occurs at the transition boundary of regimes I and II.

Influence of separator control on the characteristics of severe slugging flow

Due to the special structure of offshore multiphase pipes, it is easy for severe slugging to occur in the riser at low gas-liquid velocity. Violent pressure fluctuations and dramatic changes of flow rate are the main characteristics of severe slugging, leading to the risk of serious damage. In this paper, the separator control is adopted to accurately control the separator liquid level and pressure under severe slugging flow conditions. This indicates that the separator liquid level control alone does not have a significant impact on the upstream flow, but it is beneficial for normal operation and pressure control of the separator. As the separator pressure increases, the peak pressure in the riser apparently diminishes, and the amplitude of pressure fluctuation gradually decreases, which means that severe slugging is inhibited. During the slug blowing out, the gas/liquid slipping in the riser intensifies. The long gas plug quickly flows through the riser, and then tends to morph into short and slowly flowing gas bubbles. The elimination effect of the pressure control strategy on severe slugging is related to the relative rate of the superficial gas/liquid flow.

Multiphase flow model developed for simulating gas hydrate transport in horizontal pipe

The hydrate formation or dissociation in deep subsea flow lines is a challenging problem in oil and gas transport systems. The study of multiphase flows is complex while necessary due to the phase changes （i.e., liquid, solid, and gas） that occur with increasing the temperature and decreasing the pressure. A one-dimensional multiphase flow model coupled with a transient hydrate kinetic model is developed to study the characteristics of the multiphase flows for the hydrates formed by the phase changes in the pipes. The multiphase flow model is derived from a multi-fluid model, while has been widely used in modelling multiphase flows. The heat convection between the fluid and the ambient through the pipe wall is considered in the energy balance equation. The developed multiphase flow model is used to simulate the procedure of the hydrate transport. The results show that the formation of the hydrates can cause hold-up oscillations of water and gas.

Numerical simulation research on multiphase flow of aviation centrifugal pump based on OpenFOAM

This paper aims to tackle the calculation efficiency problem raised in the cavitation-flow simulation of the aviation centrifugal pump due to the fading-away interface resulting from the dissipation of numerics used in the phase-change control equation for unstructured-grid multiphase flow,and due to the limitation of flow time-step in whole flow regimes,the control equation of vapor–liquid two-phase flow considering cavitation mass transport is established firstly,modifying the momentum equation by introducing the surface tension,and adding the artificial convective flow to the phase equation to solve the numerical dissipation problem.Secondly,in consideration of the local time step principle and based on the multi-dimensional general limiter algorithm with explicit solutions under the OpenFOAM platform,a solution method of steady-state VOF (Volume of Fluid) model considering cavitation two-phase change is constructed,and the feasibility of this method is verified by NACA hydrofoil and NASA flat plate inducer.Finally,based on the platform developed,the cavitation performance of an aviation centrifugal pump inducer is analyzed.The research results show that the error of the calculated cavitation pressure distribution for NACA hydrofoil between the simulation test and the experimental-test is less than 5%,and the maximum error of calculated cavitation number at pump head dropping for NASA high-speed flat plate inducer between the simulation test and the experimental-test is 2.1%.The cavitation area observed in the simulation test is the same as that obtained in the high-speed photography test.Based on the OpenFOAM simulation method,the position of pump head dropping of the fuel centrifugal pump can be accurately captured.The error of the calculated cavitation number at pump head dropping between the simulation test and the experimental test is about 3.7%,showing high calculation accuracy.

A CFD Study on the Mechanisms Which Cause Cavitation in Positive Displacement Reciprocating Pumps

A transient multiphase CFD （computational fluid dynamics） model was set up to investigate the main causes which lead to cavitation in PD （positive displacement） reciprocating pumps. Many authors agree on distinguishing two different types of cavitation affecting PD pumps： flow induced cavitation and cavitation due to expansion. The flow induced cavitation affects the zones of high fluid velocity and consequent low static pressure e.g. the valve-seat volume gap while the cavitation due to expansion can be detected in zones where the decompression effects are important e.g. in the vicinity of the plunger. This second factor is a distinctive feature of PD pumps since other devices such as centrifugal pumps are only affected by the flow induced type. Unlike what has been published in the technical literature to date, where analysis of positive displacement pumps are based exclusively on experimental or analytic methods, the work presented in this paper is based entirely on a CFD approach, it discusses the appearance and the dynamics of these two phenomena throughout an entire pumping cycle pointing out the potential of CFD techniques in studying the causes of cavitation and assessing the consequent loss of performance in positive displacement pumps.

基于RBF的油气水段塞流流型超声识别方法

石油管道内的多相流流型识别主要集中在气液两相流和油水两相流方向且准确识别流型范围有限,为了解决油气水段塞流流型识别问题,本文提出一种基于RBF神经网络和超声传播规律的油气水段塞流流型识别方法。根据油气水段塞流的相分布特点,建立了流型识别超声测试仿真模型。采用超声透射衰减技术和反射回波技术研究水平管道油气水三相段塞流超声响应特性,提取透射衰减信号区分段塞流液膜区、气泡夹带区和稳定液塞区。利用反射信号时间序列数据中的回波能量等统计特征,通过RBF神经网络对油气水段塞流进行流型识别。结果表明,基于超声传播机理以及RBF神经网络三相段塞流流型识别率为95.7%。基于RBF神经网络的流型识别算法研究为超声技术实现水平管油气水段塞流流型识别提供了理论基础。

The simulation of multiphase flow field in implantable blood pump and analysis of hemolytic capability

The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and the shear stress distribution is obtained. A hemolytic prediction model based on the shear stress is built based on the calculation results, and it can be used for qua- ntitative predictions of the hemolytic behavior of a blood pump. Hemolysis tests in vitro were performed 6 times with fresh bovine blood. At each time, the flow of the pump NIVADIII is 5 L/min and the outflow tract pressure is 100 mmHg. According to the tests, the plasma free hemoglobin （FHB） content and the hematocrit （HCT） are measured after 0 s, 0.5 s, 1 s, 1.5 s 4 s. At the end of each experiment Normal Index of Hemolysis （NIH） of NIVADIII is calculated. The average of NIH is 0.0055 g/100L, almost identi- cal with that obtained from the hemolytic prediction model. This method can be applied in the selection stage of a blood pump.

新型脱色方法对烷基糖苷脱色效果的影响

通过一步法合成烷基糖苷后,在漂白时采用强力自吸多相流泵,使漂白体系从常规的搅拌体系变成循环体系,对采用此新型脱色方法和普通方法的漂白过程中的现象进行分析,并对漂白产品的检测数据进行对比.考察了新型脱色方法的温度、pH及泵的参数变化对产品的影响,得到了最佳的漂白脱色条件:脱色温度控制在70~80℃,pH控制在12左右,泵的流量控制在40 m3/h。上述条件下,得到的产品色泽浅、质量好。

射流泵注采工具旁通阀密封性能及多相流体流动分析

近年来,射流泵注采一体化技术在海上稠油油田的应用日益广泛。为促进该技术的大规模推广,采用实验结合数值模拟的方法,分析射流泵球头附近密封性能以及流动情况。研究得出如下结论:常温与高温工况下注采旁通阀的密封性能良好;球头形状及材料须进一步研究;过流通道附近气液两相流动引发复杂的压力与速度变化,须重点关注。

泵站内部流动分析方法研究进展

泵站是调水、供水、灌溉和排水系统重要基础设施,其水力性能直接影响系统的安全性、稳定性和工程效益。泵站内部流动分析涉及泵站、流体动力学和数值理论等多个学科,分析方法已由传统的一维半经验半理论阶段发展到了基于计算流体动力学的现代三维黏性阶段。本文综述了泵站内部流动分析过程中涉及的湍流模型、几何模型、网格模型、数值离散模型和解算模型,阐述了研究泵站进水池表面旋涡、泥沙与空化特性、水力激振特性、水力瞬变特性及水力设计的基本方法和过程,总结了泵站流动分析方法方面的最新研究成果,展望了未来发展趋势及主要研究课题。

单压吸收式制冷系统气泡泵理论模型与实验研究

应用两相流分相模型理论,对单压吸收式制冷系统中气泡泵在绝热弹状流工况下的工作特性进行理论分析,建立了气泡泵的理论模型。并以饱和水为工质,对气泡泵的稳态工作过程进行了实验研究,实验结果与理论分析结果相一致。分析结果表明,气泡泵提升管的两相流流型与气体流量及沉浸比有关;随着气体流量或沉浸比的增加,提升管中两相流流型将发生改变,从而使实验结果与理论分析曲线逐渐偏离;流型的改变只是使液体提升量随气体流量增加的增速减缓,对液体提升量并无抑制作用。分析结果对气泡泵的优化设计提供了理论和实验依据,对单压吸收式制冷机性能的提高具有重要意义。

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。

自控泵吸法消除强烈段塞流

在海洋油气开采过程中，当海底混输管线到达海洋平台时，需与上升管连接，从而构成了集输一上升管系统。而在油田开采后期，由于气液相速度较低，该系统中易形成强烈段塞流。由于该流型在生产实际中会带来许多问题，例如系统中压力的剧烈波动以及长液塞的出现会造成分离器的控制困难，甚至出现生产中断，同时在深海油田中强烈段塞流现象会产生很高的背压，对油藏造成不利的影响，甚至出现死井。因此，深入系统地研究强烈段塞流的发生机理和流动特征，探索消除强烈段塞流的可行方法，是我国海洋油气工业油田开发过程中亟须解决的科学问题。

管式液塞捕集器设计及性能测试研究

管式液塞捕集器是气液混输管线终端的重要设备,其设计参数复杂,目前国内还没有具有独立知识产权的液塞捕集器产品。为此,研究了混输管线段塞流参数变化规律,指出捕集器的液位控制系统对捕集器的工作性能有较大影响——不使用液位控制系统时,捕集器液位和压力都不稳定,影响捕集器的工作性能。而启动液位控制系统后,捕集器压力和液位都较稳定;启用液位控制系统以后,捕集器内液位在设定值附近周期性波动,受液位波动影响,捕集器内压力也出现周期性波动,液位和压力的波动周期与液体流量有关。编制了段塞流捕集器设计规则,建立了捕集器系统的优化数学模型,设计并优化了液塞捕集器的结构与尺寸。所研制的液塞捕集器经室内测试,运行状态良好,在不同的试验工况下,捕集器内部的压力、液位都比较平稳,可以较好地分离气、液两相,有效消除段塞流的影响。

上升管系统中严重段塞流的液塞速度特性

During the exploitation of offshore oil,it is easy to form severe slugging in the riser system at a low gas-liquid velocity.The magnitude of the pressure fluctuation can be significantly high,causing dramatic change of flow rate and leading to other damages.In this paper,the characteristics of slug velocity during the four stages of severe slugging in the pipeline-riser system were studied.It was found that the slug head rose in the riser at a constant velocity in the slug formation stage.At the same time,the direction of slug tail movement was opposite to the flow direction,and the tail velocity kept constant when flowing through the inclined pipe.In the process of blowout,the liquid velocity in the pipeline-riser system increased and reached a maximum value when the slug tail reached the top of the pipeline-riser.At this moment,the instantaneous flow rate was much larger than that in the slug production stage.

离心泵气液固多相流动数值模拟与试验

为研究离心泵输送含有气固液多相时内部的流动情况,采用Pro/E三维造型软件进行几何造型,基于ANSYSCFX软件应用雷诺时均方程、双方程湍流模型,并结合SIMPLEC算法对其内部三维气固液多相流各相流动规律进行数值计算,将计算结果与试验结果进行对比结果表明:受气相所产生旋涡的影响,固相体积分数在径向量纲位置r/R2为0.4时达到最大值后直线急剧下降,下降至一定值后开始波动变化,而气相体积分数在径向量纲位置r/R2为0.4时较小,从径向量纲位置r/R2为0.4以后急剧增大。气、固两相互相影响对方颗粒的分布。气相主要集中在叶片工作面的中间位置,气相的存在使叶轮流道内产生旋涡,影响叶轮流道内的能量交换与传递;固相在没有旋涡的流道内是紧靠叶片表面运动的,在有旋涡流道内主要是随着旋涡旋转方向进行流动,固相所占比值的增加对流动轨迹的影响并不明显。对气液固多相流的深入研究和应用提供了有价值的参考。