Computational Analysis of Centrifugal Pump Delivering Solid-liquid Two-phase Flow during Startup Period

The transient behavior of centrifugal pumps during transient operating periods, such as startup and stopping, has drawn more and more attention recently because of urgent needs in engineering. Up to now, almost all the existing studies on this behavior are limited to using water as working fluid. The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet. In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow, the transient flows inside the pump are numerically simulated using the dynamic mesh method. The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time, and are written into computational fluid dynamics （CFD） code-FLUENT by using a user defined function. The predicted heads are compared with experimental results when pumping pure water. The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process. Moreover, the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water. The solid-liquid two-phase flow results in a higher impeller shaft power, a larger dynamic reaction force, a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water. The research may be useful to tmderstanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.

Numerical simulation of predicting and reducing solid particle erosion of solid-liquid two-phase flow in a choke

Chokes are one of the most important components of downhole flow-control equipment. The particle erosion mathematical model, which considers particle-particle interaction, was established and used to simulate solid particle movement as well as particle erosion characteristics of the solid-liquid two-phase flow in a choke. The corresponding erosion reduction approach by setting ribs on the inner wall of the choke was advanced. This mathematical model includes three parts： the flow field simulation of the continuous carrier fluid by an Eulerian approach, the particle interaction simulation using the discrete particle hard sphere model by a Lagrangian approach and calculation of erosion rate using semiempirical correlations. The results show that particles accumulated in a narrow region from inlet to outlet of the choke and the dominating factor affecting particle motion is the fluid drag force. As a result, the optimization of rib geometrical parameters indicates that good anti-erosion performance can be achieved by four ribs, each of them with a height （H） of 3 mm and a width （B） of 5 mm equaling the interval between ribs （L）.

Pressure Drop of Liquid–Solid Two-Phase Flow in the Vertical Tube Bundle of a Cold-Model Circulating Fluidized Bed Evaporator

A cold-model vertical multi-tube circulating fluidized bed evaporator was designed and built to conduct a visualization study on the pressure drop of a liquid–solid two-phase flow and the corresponding particle distribution.Water and polyformaldehyde particle(POM)were used as the liquid and solid phases,respectively.The effects of operating parameters such as the amount of added particles,circulating flow rate,and particle size were systematically investigated.The results showed that the addition of the particles increased the pressure drop in the vertical tube bundle.The maximum pressure drop ratios were 18.65%,21.15%,18.00%,and 21.15%within the experimental range of the amount of added particles for POM1,POM2,POM3,and POM4,respectively.The pressure drop ratio basically decreased with the increase in the circulating flow rate but fluctuated with the increase in the amount of added particles and particle size.The difference in pressure drop ratio decreased with the increase in the circulating flow rate.As the amount of added particles increased,the difference in pressure drop ratio fluctuated at low circulating flow rate but basically decreased at high circulating flow rate.The pressure drop in the vertical tube bundle accounted for about 70%of the overall pressure drop in the up-flow heating chamber and was the main component of the overall pressure within the experimental range.Three-dimensional phase diagrams were established to display the variation ranges of the pressure drop and pressure drop ratio in the vertical tube bundle corresponding to the operating parameters.The research results can provide some reference for the application of the fluidized bed heat transfer technology in the industry.

Flux vector splitting solutions for coupling hydraulic transient of gas-liquid-solid three-phase flow in pipelines

The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.

Mechanism from particle compaction to fluidization of liquid–solid two-phase flow

A new model of particle yield stress including cohesive strength is proposed,which considers the friction and cohesive strength between particles.A calculation method for the fluidization process of liquid–solid two-phase flow in compact packing state is given,and the simulation and experimental studies of fluidization process are carried out by taking the sand–water two-phase flow in the jet dredging system as an example,and the calculation method is verified.

RESEARCH ON METHOD TO CALCULATE VELOCITIES OF SOLID PHASE AND LIQUID PHASE IN DEBRIS FLOW

Velocities of solid phase and liquid phase in debris flow are one key problem to research on impact and abrasion mechanism of banks and control structures under action of debris flow. Debris flow was simplified as two-phase liquid composed of solid phase with the same diameter particles and liquid phase with the same mechanical features. Assume debris flow was one-dimension two-phase liquid moving to one direction, then general equations of velocities of solid phase and liquid phase were founded in two-phase theory. Methods to calculate average pressures, volume forces and surface forces of debris flow control volume were established. Specially, surface forces were ascertained using Bingham＇s rheology equation of liquid phase and Bagnold＇s testing results about interaction between particles of solid phase. Proportional coefficient of velocities between liquid phase and solid phase was put forward, meanwhile, divergent coefficient between theoretical velocity and real velocity of solid phase was provided too. To state succinctly before, method to calculate velocities of solid phase and liquid phase was obtained through solution to general equations. The method is suitable for both viscous debris flow and thin debris flow. Additionally, velocities every phase can be identified through analyzing deposits in-situ after occurring of debris flow. It is obvious from engineering case the result in the method is consistent to that in real-time field observation.

Theoretical analysis of effect of solid phase on cavitation performance of deep-sea mining pump

In view of the present situation of low cavitation performance of deep-sea mining slurry pump, the effect of solid phase on the cavitation performance of deep-sea mining pump is analyzed theoretically. The relationship between gas and liquid phases are established by cavitation nucleon theory and mass energy equation as well as solid phase and liquid phase, and then we explored the relationship between gas phase and solid phase. The results show that the critical bubble radius and solid-phase concentration flow rate during the cavitation can be related to the liquid pressure. Eq.(19) show that the larger the solid particle concentration and the solid phase flow, the earlier the cavitation will occur, and pump anti-cavitation performance will decline.

煤层气储层气-液-固多相渗流规律研究

揭示储层非饱和流阶段煤粉运移产出规律,对煤层气高效排采具有重要现实意义。基于气-液-固三相流模拟装置,通过设定不同煤粉粒径、注入流速、裂缝宽度和煤粉质量分数等条件,开展了煤层气储层非饱和流阶段煤粉产出运移特征试验,并分析了煤粉沉淀量、产出量及煤岩气相与液相渗透率变化特征。研究表明:随着裂缝宽度增加,煤粉产出量呈现出逐渐增大的趋势,沉淀量呈现出先增大后减小的变化特征,在裂缝宽度为0.1 mm时达到最大值;随着煤粉质量分数的增大,产出量表现为先增大后减小(峰值点在0.15‰附近),沉淀量逐渐增大,说明煤粉在储层中运移存在一定的单位体积含量极值,超过极值后,煤粉将大量沉淀并堵塞孔裂隙;合理控制煤层气产水产气速率,能够有效地控制煤粉的产出,煤粉沉淀量和产出量随着注入流速的增长均呈现出先增大后减小的趋势,注入流速为5.0 mL/min时的煤粉沉积量最大,在流速为7.5 mL/min时煤粉产出量相对较高;液相渗透率演化特征呈现出逐渐降低和先稳定后逐渐降低2种变化趋势,气相渗透率演化特征较为复杂;综合注入压力、煤岩渗透率变化、煤粉产出和沉淀特征,可将煤粉在裂缝中运移划分为缓慢沉积、快速沉积和完全堵塞3个阶段。

基于CFD-DEM方法的组合管路磨损特性研究

鉴于管道磨损对于确保管道系统的安全、经济和可持续运行至关重要,基于计算流体力学——离散元耦合法(CFD-DEM),对一种由2个90°弯头组成的组合管路固液两相流磨损特性进行了数值模拟研究。结果表明,在颗粒体积浓度保持恒定的情况下,随着流速的增加,磨损率将呈指数型增长,并与碰撞速度的2.41次方成正比;随着颗粒浓度的增加,2个弯头的碰撞频率和磨损率的增长率出现了不同的变化,高浓度工况下管道内更易出现“护盾效应”;弯头间距的增大使得颗粒的流动更为充分,同时削弱了弯头内二次流的影响,导致颗粒与壁面接触的次数减少,碰撞频率和磨损率也随之降低;在相同浓度的混合粒径工况下,粒径的增加将导致弯头壁面的平均磨损率减少,然而大颗粒的惯性力增加将导致弯头壁面的最大磨损率增加。研究结果为组合管路的抗磨损性能提升提供了理论支撑。

ON EQUATION OF DISCRETE SOLID PARTICLES' MOTION IN ARBITRARY FLOW FIELD AND ITS PROPERTIES

The forces on rigid particles moving in relation to fluid having been studied and the equation of modifications of their expressions under different flow conditions discussed, a general form of equation for discrete particles' motion in arbitrary flow field is obtained. The mathematical features of the linear form of the equation are clarified and analytical solution of the linearized equation is gotten by means of Laplace transform. According to above theoretical results, the effects of particles' properties on its motion in several typical flow field are studied, with some meaningful conclusions being reached.

Erosion Characteristics of Hydraulic Turbine Guide-Vane End Clearance in Sediment Water Flow: A Simplified Model Analysis

The effect of clearance flow on the erosion characteristics of a circular cylinder with a backward facing step in sediment-laden water flow is analyzed numerically with the mixture model and the re-normalization group (RNG) k-ε turbulence model. Thirty-six monitoring points are set up on different stream surfaces to collect information on the impact erosion under different flow conditions, where the Initial Sediment Volume Fraction (ISVF) is set to 0.05, 0.075, 0.1, 0.125, and 0.15;particle diameter is set to 0.05 mm, 0.15 mm, 0.25 mm, 0.35 mm, and 0.45 mm respectively. The distribution of particle velocity and Local Solid-Phase Volume Fraction (LSVF) along different stream surfaces are calculated, based on which the trend of erosion is qualitatively evaluated. ISVF and particle diameter play different roles on the impact erosion index parameter () on the different wetted walls. Relative wear rate of numerical estimation agrees well with the practical one under the same working condition. Numerical analysis demonstrates that guide vane with a negative curvature end surface (concave surface) can decrease erosion damage effectively, which may provide a reference for optimal design and maintenance of hydraulic turbine.

欧拉-欧拉双流体模型中颗粒黏性对液固散式流态化的影响

采用无黏性双流体模型、基于颗粒动理学的双流体模型以及Brandani和Zhang简化双流体模型探究了颗粒黏性对液固散式流化特性的影响规律。经与文献中实验数据和Gibilaro公式计算值对比后发现:3种双流体模型均能较好地预测整体固含率,与实验值相对偏差在3%以内,其中无黏性双流体模型和简化双流体模型对固含率预测更符合散式流态化特点;3种双流体模型对时均颗粒轴向速度预测均呈现整体环核结构的固有属性,其中简化双流体模型在较低和较高两组液速工况下预测的相对偏差平均值分别为0.277和1.028;当入口液速突然变化后,收缩过程中简化双流体模型对响应时间预测准确度略高,而膨胀过程中因低浓度区界面不稳定以及膨胀过程中床内颗粒形成的由浓到稀过渡段延长了稳定时间,3种模型预测均与理想过程存在一定偏差,其中液速较低时三者差异不明显,但液速较高时简化双流体模型准确性略高。基于颗粒动理学的双流体模型对动态过程模拟的计算耗时最长。

基于A-RAFT模型的垂直管道输送测速方法

流速作为流动特性的重要参数之一,在垂直管道提升效率研究中有着重要地位.以管道固液两相流为研究对象,研究管道测速的方法.结合深度学习技术,提出了基于注意力机制的光流全场递归匹配模型(A-RAFT),提高了网络对速度场突变区域的估计能力;构建了一个虚实结合的数据集,用于训练神经网络模型.对新提出的模型与数据集进行评估,结果显示:该模型在合成的图像上实现了高精度的速度场计算,与现有其他模型相比,估计误差减小了15.6%;开展了垂直管道固体颗粒输送的模拟实验,本模型在实验中所采集的真实流场数据上同样展现了准确的估计性能,该模型对颗粒速度的测量平均相对误差低于5%.上述实验结果充分证明了该方法在速度场中有较高的估计精度,模型有较强的泛化能力.这一研究能够为能源开采、隧道掘进、污水处理以及长距离管道运输等领域中的固液两相流特性分析提供新思路.

基于CFD-DPM的离心泵内颗粒性质对泵性能与磨损的影响

为揭示离心泵在输送固液两相流时颗粒密度和粒径对泵性能和磨损的影响,采用Realizable k-ε湍流模型(液相)和DPM离散相模型,对模型泵内固液两相流动进行定常数值模拟,研究固液两相流场中颗粒的运动轨迹以及磨损规律。结果表明:随着颗粒密度和粒径的增大,模型泵的扬程和效率均下降;密度、粒径越大的颗粒,其运动轨迹越易偏向叶片工作面;随着颗粒密度的增加,叶片工作面以及蜗壳内的磨损程度加剧,但是叶片背面的磨损减轻,颗粒相应地在叶片工作面和蜗壳外壁边缘聚集;随着颗粒粒径的增大,蜗壳整体磨损程度加重,其中蜗壳的隔舌区域、Ⅱ区域和Ⅵ区域磨损程度最严重;叶片整体磨损程度逐渐降低,且叶片工作面磨损程度大于叶片背面。

基于加压酸浸锰烟尘过程中固-液两相流体力学特性CFD模拟

将欧拉-欧拉(E-E)双流体模型、颗粒动力学理论(KTGF)与k-ε湍流模型耦合,以搅拌速度、固相体积分数为变量探究对釜体内液相速率、液相湍流动能的影响.结果表明:釜体内的液相速率、湍流动能与搅拌速度成正相关,且与固相体积分数的大小成负相关.当固体体积分数为2.5%、7%、13%,对应液相速度下降幅度为8%,16.2%,18.4%,对应湍动能下降幅度为7.6%,13.2%,20.6%.

立式搅拌釜中固-液混合特性模拟研究

研究固-液混合特性对生产效率、能耗等指标的优化具有重要意义,实际生产中立式搅拌釜应用较多,本文采用CFD方法和DEM方法从颗粒密度、粒径、搅拌速度和初始液面高度等4个方面对立式搅拌釜的颗粒混合特性进行了数值模拟研究,并且从速度场、湍动能分布和颗粒混合度3个维度来评判颗粒的混合特性。结果表明,在这些影响因素中,颗粒密度和搅拌速度对混合特性的影响最大,特别是当颗粒密度为1200 kg/m3时,相对标准差值达到0.5左右,说明混合程度较好;搅拌速度越大,混合性能越好;颗粒粒径对混合性能的影响较小,但粒径越小,越容易悬浮,粒径增大,混合程度降低;初始液面高度的改变导致固含率的改变,但是对固液混合性能基本不产生影响。

复合管道内液-固两相流浆体水击压强计算

对于单一管道的单相液体水击现象计算已经比较成熟,但是很少有对于复合管道的液固两相流系统的浆体水击 计算方面的报道。根据实际工程设计需要,提出了具有复合管道的液-固两相流浆体水击压强的计算方法。同时对某电厂 液一固两相流输灰系统浆体水击压强进行了计算与分析,提出了防止浆体水击的措施。

液固两相介质流中Cu-Cr-Zr合金的冲蚀磨损行为

利用MCF-30冲蚀磨损实验机,对固溶态及随后经过不同形变热处理的Cu-Cr-Zr合金进行液固两相流冲蚀磨损实验,并运用扫描电镜对其微观形貌进行观察与分析。结果表明：在两种不同介质冲蚀磨损实验中,固溶态合金冲蚀磨损质量损失最大,且随形变时效后加工变形程度的增大,冲蚀磨损质量损失呈先逐渐下降然后上升的变化趋势;添加少量石英砂（10 g/L）后,合金冲蚀磨损质量损失约增加19%-35%;铜合金线材二次加工变形率在50%-80%之间时,具有良好的抗冲蚀磨损性能。

控压钻井节流阀液-固两相流冲蚀预测及验证

运用欧拉-拉格朗日法和离散相模型,预测了节流阀内部粒子运动和分布规律,利用半经验冲蚀模型求解了颗粒对阀芯的冲蚀率,并设计相关实验验证了数值模拟的准确性。结果表明,数值模拟能够较为精确地预测节流阀阀芯的冲蚀轮廓;5 h以内的预测冲蚀损失量与实验数据贴合度很高,5 h以后的预测数据经合理修正后与实验结果相近,随冲蚀时间增长,预测误差逐渐减小,最终达到1%以下;该模型能够用于预测控压钻井节流阀复杂流场的冲蚀,有望为控压钻井节流阀的进一步优化设计提供参考。

基于CFD-DEM方法的变径T型流道冲蚀特性研究

目的研究石油开采过程中,携砂压裂液对变径T型流道壁面冲蚀磨损规律及主要影响因素。方法针对石油压裂管汇及井下喷砂器等工具中常见的变径T型流道的冲蚀问题,建立了基于CFD-DEM的变径T型流道固液两相流冲蚀磨损预测模型,该模型中颗粒-颗粒、颗粒-壁面碰撞采用逆向迭代碰撞搜索算法,颗粒-流体耦合计算时间步长根据耦合收敛条件自适应调整。将数值方法与正交试验方法结合,分析各因素变化对均值主效应响应的优先排序和各因素的交互作用,并进行了单因素变化对冲蚀规律的影响。结果单因素分析时入口流速增大,T型流道最大冲蚀速率和冲蚀面积均增大,冲蚀位置向支流道出口处移动,流体携带颗粒能力增强,堆积颗粒数量减小。砂比范围为5%~35%时,最大冲蚀速率与砂比正相关。最大冲蚀速率随粒径的增大而先增大后减小,随变径比的增大而减小。与最大冲蚀速率均值主效应分析结论一致,验证了正交试验结论的准确性。结论径向流速、切向流速、管壁压力、最大冲蚀速率为衡量变径T型流道冲蚀程度的指标时,入口流速的影响最大,其次是支撑剂粒径、变径比、砂比,入口流速与其他因素的交互作用对冲蚀速率的影响最显著。