Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump units.The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model.UDF(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology.The results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually decreases.And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner.The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude.The mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values.Compared with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and leakage.During actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

Experimental Study and Simulation Principles of An Oil-Gas Multiphase Transportation System

Presented is an experimental study on the performance of an oil-gas multiphase transportation system, especially on the multiphase flow patterns, multiphase pumping and multiphase metering of the system. A dynamic simulation analysis is conducted to deduce simulation parameters of the system and similarity criteria under simplified conditions are obtained. The reliability and feasibility of two-phase flow experiment with oil and natural gas simulated by water and air are discussed by using the similarity criteria.

Performance Prediction of the Helico-axial Multiphase Pump

A modified one-dimensional model is developed for prediction of multiphase pump performance. Taken into account in the model are the gas compressibility, the slip speed gap between two phases and the flow cross-sectional depth gradient in the flow line. By using this model, we can select appropriate geometrical parameters of the impellers and guide vanes, and thus higher-pressure boost is obtained but phase separation does not occur. Accordingly, the design method can be optimized. The drag coefficients are analyzed for different flows. Results predicted by the modified model are compared with a series of experimental data and found in good agreement. This model provides a convenient and economical tool for engineering design over a traditional one.

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.

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.

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.

工况对双螺杆混输泵振动特性影响实验

为研究工况对双螺杆混输泵振动特性的影响,搭建双螺杆混输泵多通道振动测试系统,测试并分析不同含气率、转速及出口压力下混输泵振动参数。结果表明:排液开始时排液腔瞬时打开诱发射流,射流向竖直向的泵出口偏转从而产生压力脉动并诱发振动,导致泵竖直方向振动加速度有效值高于水平方向和轴向;含气率为7.5%时振动加速度有效值为纯液工况时的1.88倍,随着含气率进一步升高测量值降低;而含气率大于20%时,振动有效值继续升高。在转速为1450r/min时y方向振动加速度有效值是850r/min时的2.95倍;振动加速度有效值随出口压力变化较小。当转速由850r/min升高至1450r/min时,径向垂直方向振动加速度主频由75fn移动至50fn。研究可为提高双螺杆混输泵运行稳定性提供指导。

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.

Optimization design of multiphase pump impeller based on combined genetic algorithm and boundary vortex flux diagnosis

A novel optimization design method for the multiphase pump impeller is proposed through combining the quasi-3D hydraulic design（Q3DHD）, the boundary vortex flux（BVF） diagnosis, and the genetic algorithm（GA）. The BVF diagnosis based on the Q3DHD is used to evaluate the objection function. Numerical simulations and hydraulic performance tests are carried out to compare the impeller designed only by the Q3DHD method and that optimized by the presented method. The comparisons of both the flow fields simulated under the same condition show that（1） the pressure distribution in the optimized impeller is more reasonable and the gas-liquid separation is more efficiently inhibited,（2） the scales of the gas pocket and the vortex decrease remarkably for the optimized impeller,（3） the unevenness of the BVF distributions near the shroud of the original impeller is effectively eliminated in the optimized impeller. The experimental results show that the differential pressure and the maximum efficiency of the optimized impeller are increased by 4% and 2.5%, respectively. Overall, the study indicates that the optimization design method proposed in this paper is feasible.

沙粒粒径对高比转速离心泵非定常特性的影响

在离心泵实际运行环境中,固液两相流中存在的沙颗粒会直接影响离心泵运行的效率及稳定性,因此,以一比转速ns=157的离心泵为例,对不同粒径沙粒在泵中的运动特性进行了仿真模拟分析。首先,采用CFturbo及UG等软件对离心泵进行了三维建模及优化处理,使用ICEM软件对模型进行了全流域网格划分,使其达到了计算精度要求;然后,利用ANSYS商业软件进行了计算前处理,再结合Mixture多相流模型与Finnie磨损模型设计了五种不同沙粒粒径,并对其进行了全流道仿真模拟;最后,根据仿真计算结果分析了不同粒径沙粒在泵流道中的运动分布、磨损情况及其对泵的瞬态影响。研究结果表明:在粒径为0.04 mm~0.2 mm范围内,沙粒直径每增大0.04 mm,泵扬程降低1.3%左右,效率降低0.6%~1.5%;沙粒主要聚集在叶片吸力面外侧尾缘处、泵前盖板、蜗壳隔舌处,且其浓度与沙粒粒径大小呈正比关系;沙粒粒径每增加一个梯度,其在吸力面分布面积将增加约5%,最高占叶片面积约35%;由于结构差异,在蜗壳流道内,低直径沙粒更容易悬浮在流道中造成聚集,在叶轮流道中较大直径的沙粒会由于摩擦力而聚集;以粒径0.08 mm为界,小直径沙粒引起的压力脉动幅值与径向力增长的速率均小于大直径沙粒。

多相混输泵用超高压机械密封性能研究

针对超高压混输泵机械密封易磨损失效的问题,介绍了端面槽加工和涂层应用两种策略,用热流固耦合分析方法,分析了浅槽微接触式机械密封在实际应用中的温度分布和端面变形情况,阐述了表面涂层技术的应用,进行了一系列机械密封性能的试验研究。研究结果不仅证实了这些技术在提高机械密封寿命和可靠性方面的有效性,还证实了端面开槽和涂层技术在降低摩擦、改善耐磨性能方面的显著效果。为超高压混输泵机械密封系统的设计和优化提供了重要的理论依据及实践指导。

Temperature and thermodynamic deformation analysis of the rotors on a twin screw multiphase pump with high gas volume fractions

The pressure increasing process within a twin screw multiphase pump, under the condition of high gas volume fractions (GVFs), induces large temperature and pressure changes that cause the rotors to deform. Rotor deformations heavily influence the backflow of the multiphase fluid through clearances within the twin screw multiphase pump and these deformations may even lead to pump failures. An accurate temperature and pressure distribution on the screw rotors need be obtained before the deformation analysis can be carried out. By means of small temperature and pressure sensors embedded into the groove at the root of the rotors, the temperatures of 12 points on the rotors and the pressure distributions of a twin screw multiphase pump under high GVFs conditions were recorded. Temperature test results were adopted to perform a heat transfer analysis for determining the temperature distribution on the screw rotors. Then deformation analyses, including thermal deformation, force deformation, and total deformation, were conducted according to the pressure and temperature distributions. Deformation analysis for different materials was also conducted under the same boundary conditions. A material was suggested for the manufacturing of rotors in a twin screw multiphase pump under the condition of high gas volume fractions.

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.

Pressure fluctuation characteristics in the pressurization unit of a multiphase pump

The tip clearance induces the tip leakage vortex(TLV),which has a great impact on the pressure fluctuation characteristics of the multiphase pump.To investigate the effect of the tip clearance on the pressure fluctuations,based on the Reynolds time-averaged Navier-Stokes equation and the shear stress transfer(SST)k-ωturbulence model,the three-dimensional turbulent flow in the pump is numerically simulated for different tip clearances in the water and gas-liquid two-phase cases by using the ANSYS CFX software and the results are verified with experimental data.It is shown the greater pressure fluctuation intensity corresponds with the TLV both in the water and gas-liquid two-phase cases.In the meantime,the location of the maximum pressure fluctuation intensity is related to the tip clearance size.In addition,for different tip clearances,the pressure fluctuation intensity with the rotor and stator interaction(RSI)is relatively larger.The difference is that when R_(tc)=1.5 mm,the pressure fluctuation intensity near the impeller middle point is also relatively larger.On the whole,the pressure fluctuation intensity in the gas-liquid two-phase case is larger than that in the water case.Furthermore,the gas causes the frequency of the high-amplitude pressure fluctuation in the impeller and the diffuser to be shifted from 7 f_(n)(f_(n) denotes impeller rotational frequency)and 3 f_(n) to the low-frequency region,respectively.The pressure fluctuations at the blade-passing frequency(BPF)and the multiple BPFs gradually disappear.Meanwhile,the amplitude at the dominant frequency in the gas-liquid two-phase case is at least one order of magnitude smaller than that in the water case,and the peak-to-peak value of the pressure fluctuation is also much smaller.

基于空泡溃灭势能的泵内空化空蚀特性

针对一双吸式离心泵内部空化流动特性及空蚀问题,开展了基于多相空化模型和空泡溃灭势能的泵内空化空蚀特性分析.基于流体体积法(VOF)和Schnerr-Sauer空化模型,并结合非定常RNG k-ε湍流模型,对双吸泵内全流场及空化流动特性开展了模拟分析.在此基础上,基于空泡溃灭势能建立空蚀风险评估方法,分析了由于泵内空化造成的空蚀风险区域.最后,基于熵产方法分析了空化造成的泵内能量损失特性及空泡产生溃灭与能量损失的关联.结果表明:该空化流动计算方法能准确模拟双吸泵扬程的变化趋势、空泡的产生过程以及空化时叶轮流道内的流动特性;空蚀风险预测结果表明:空蚀主要分布在叶轮吸力面及叶轮前盖板并位于空泡尾缘附近,且叶片表面的空蚀风险高于前盖板;泵内能量损失与空泡的产生溃灭密切相关,1个周期内能量损失极大值发生在空泡溃灭时刻.

分流叶片前缘形状对叶片式混输泵性能的影响

叶片式混输泵在气液工况下极易产生叶顶泄漏涡和气液分离的情况,这会直接导致泵的性能下降,从而影响泵的输送效率致使生产成本增加。针对上述问题,基于CFD仿真对泵的叶轮引入分流叶片进行改型,并探索分流叶片前缘形状对泵性能的影响。研究结果表明:3种分流叶片前缘形状下的模型扬程均高于原模型,其中以曲率连续方案的扬程最大,为10.85 m,扬程和效率相比原模型分别提高31.83%和2.58%;当分流叶片厚度减小时,分流叶片前半部抑制介质分离的能力得到提升,液相在分流叶片吸力面的附着力增强;受带状泄漏涡被抑制的影响,曲率连续方案下叶轮内介质流动紊乱程度低,该抑制量化为叶轮进口液相减阻5.07%和气相减阻3.80%。研究结果可为后续混输泵的优化设计提供参考。

分流叶片对多相混输泵叶轮做功性能的影响

为了提高螺旋叶片多相混输泵的做功性能,借鉴常规长短叶片离心泵的设计方法,设计了一种带有分流叶片的螺旋叶片式多相混输泵,通过采用数值计算加以试验验证的方法深入探究了设计有分流叶片后多相混输泵叶轮的做功性能。结果表明:随着进口含气量和流量的增加,原模型和分流叶片模型总功率和静功率均逐渐增加且各截面上的静功率占比远超动功率。功率分布的变化表明分流叶片会引起叶轮进口截面的静功率下降且低于原模型,出口截面的动功率增加且高于原模型,致使叶轮进口区域的做功能力被削弱,但不影响叶轮主要做功区间位置,而且还提升了叶轮总功率且该提升量主要受益于动功率的增加。研究结果对螺旋叶片式多相混输泵的结构改型和性能提升有十分重要的参考价值。

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。