液固两相流压降规律及超声法压降测量

液固两相流广泛存在于能源动力、石油化工等工业过程,两相流压降作为重要的流动参数,有助于流动建模及流态分析。建立液固两相压降测量模型,提出了一种结合超声多普勒及超声透射衰减的液固两相超声压降测量方法。搭建液固两相流动实验平台,对两相压降规律进行研究。两相混合流速和固相体积分数升高时,液固两相压降均逐渐增加。在固相体积分数为0.28%～1.37%,两相混合流速为0.9～1.65 m/s时,根据液固两相压降测量模型及Churchill模型的超声法得到的两相压降与差压传感器测量的压降平均相对误差为4.93%和5.10%,验证了测量模型的准确性。针对非均匀分布的两相流态进行压降测量,进一步拓展了压降测量模型的应用范围。本研究工作为非侵入超声法测量液固两相压降提供了方法基础。     

基于蒙特卡罗模型的高浓度浆液细度在线测量

近年来颗粒粒径测量问题受到了国内外的广泛研究。 针对燃煤电厂高浓度脱硫石灰石浆液细度在线测量,将基于蒙特 卡罗方法的声衰减模型拓展至高浓度范围,高浓度蒙特卡罗模型(HC-MCM)预测衰减系数与实验测量值相吻合。 构建 HC-MCM 矩阵用于颗粒粒径分布的反演可减小计算时间,且差分进化算法的计算结果与设定粒径和分布宽度的相对误差小于 1% 。 搭建基于透射和反射法的双模式超声检测装置并开发软件测量系统,加工适用于高浓度浆液细度测量的透射传感器和超声探 针,依托燃煤电厂完成长达 168 h 的浆液细度在线测量实验。 结果表明,两种模式超声衰减谱的变化趋势和数值大小基本吻 合。 粒径分布参数 DV50 与激光粒度仪测量结果的相对误差小于 8% ,其粒径分布满足燃煤电厂成品石灰石浆液的细度要求。     

大颗粒下螺旋离心泵内运动特性数值模拟与分析

以150×100LN-32型螺旋离心泵为模型,采用欧拉多流体、RNG k-ε模型对其内部进行三维数值模拟。对比不同颗粒粒径以及浓度情况下固液两相流场,分析了在大颗粒情况下,固体颗粒在螺旋离心泵内的运动情况。通过固相体积分数、压力以及速度分布,得出了大颗粒固液两相流在螺旋离心泵内的运动特性。并以此为参照,分析大颗粒情况下螺旋离心泵磨损情况。     

离心式污水泵叶轮磨损的数值模拟

针对离心污水泵内固液两相流动比较复杂的情况,用含沙水为工作介质,通过改变沙粒粒径和含沙水颗粒浓度的方法,对小粒径颗粒在离心污水泵内的流动进行了数值模拟。借助弄清内流场的速度、压力与颗粒分布,分析了粒径大小对泵内固体颗粒运动的影响和进口初始颗粒浓度对泵内压力和固相分布的影响,得出压力沿叶轮吸力面和压力面的分布规律以及固体颗粒沿叶片吸力面和压力面的分布规律,并在此基础上得出了离心污水泵叶轮的磨损特性。     

双叶片螺旋离心泵固液两相流特性研究

为研究双叶片螺旋离心泵叶轮内固液流动特性,采用Eulerian多相流模型,扩展的标准k-ε湍流方程以及SIMPLE算法,应用流体动力学软件对双叶片螺旋离心泵叶轮内固液两相湍流进行了数值模拟。分析了多粒径及初始固相体积浓度条件下的固相体积浓度分布规律。通过分析可得到固体颗粒存在由叶片压力面向吸力面迁移的趋势,同时有从轮毂侧向轮缘侧运动的趋势;通过外特性分析得到了相同粒径下水泵扬程随固相浓度的升高而减小,相同固相浓度下水泵扬程随粒径的增大而减小的变化趋势。     

小粒径固液两相流在旋流泵内运动的数值模拟

为了分析旋流泵内固液流动特性,采用Eulerian多相流模型,扩展的标准κ-ε湍流方程与SIMPLEC算法,应用流体动力学软件FLUENT对旋流泵叶轮内固液两相湍流进行了数值模拟。分析了多种粒径及浓度条件下的固相体积浓度分布规律。在旋流泵叶轮固液两相流动中,固体颗粒还是主要集中于叶轮工作面,因而会加剧叶轮工作面磨损破坏速度。数值结果表明,泥沙颗粒直径变大以及泥沙浓度的加大都会使旋流泵扬程和效率下降,其中浓度的变化对扬程和效率的影响更明显。     

螺旋式纸浆离心泵内部流动的数值模拟

为分析螺旋式纸浆离心泵内部流动状态，给优化过流部件结构的优化设计提供基础，采用CFD分析软件Fluent对螺旋式离心泵内部单相流动和固液两相流动进行了数值模拟。给出了螺旋式叶轮建模方法和流场分析方法，分析了泵内流体速度和压力的分布特性，并基于流动模拟结果预测了水力性能，单相输送条件下的计算结果与试验结果取得了较好的一致。通过对一定体积浓度和颗粒粒径下固液两相流的研究计算，分析了螺旋式离心泵叶片表面以及流道内的固液相分布状态，对螺旋式结构的优化具有一定的参考意义。     

固相粒径对深海采矿矿浆泵空化特性影响的规律

针对深海采矿矿浆泵空化现象,研究固相粒径对其空化特性的影响。根据空化核子理论、质能方程建立气液两相之间的质量转换方程,运用Fluent软件和Singhal et al的空化模型对在不同固相颗粒粒径工况下的深海采矿矿浆泵进行稳态全流道空化仿真研究。分析叶轮叶片背面压力和气相体积分布规律,对不同区间气相体积分数进行统计,计算出不同颗粒粒径下泵的空化余量和扬程。研究结果表明:随着固相颗粒的增大,叶轮叶片背面入口处的低压区面积逐渐扩展,泵的空化现象趋于严重,扬程下降。当粒径为25 mm时空化余量陡降至最低1.11m,空泡分布广泛,部分区域体积分数高达0.9;粒径从10 mm到25 mm的过程中扬程下降了8.67 m;继续增大粒径,泵的空化性能有所提升,空化余量稳定在3.5 m,但泵的扬程在空化和颗粒磨损共同作用下继续下降至65.3 m。     

超短接触旋流反应器分离腔气固分离特性的数值模拟

采用欧拉模型对超短接触旋流反应器内的气固两相流场进行了数值模拟,主要研究了分离腔内气固两相的分离过程。具体考察了导叶下部柱段与锥段分离空间以及排剂口附近固相体积分数的分布情况,评估气固两相在分离腔不同部位的分离效果,重点对比分析了固相粒径差异对流动情况以及颗粒聚集的影响规律。计算结果表明:5μm颗粒在分离腔的浓度分布规律不同于10μm和30μm颗粒,由于颗粒粒径较小易被气流携带,在分离空间以及排剂口都出现了不同程度的返混,对分离不利。     

超细颗粒悬浊液超声衰减谱与声速谱测量研究

将短时傅里叶变换应用于超细颗粒两相介质中超声脉冲信号处理和时频谱联合分析,采用变声程方式,提出了一种对超细颗粒两相介质声衰减谱与声速谱同时测量的方法,并对平均粒径281nm的ZnO-H2O悬浊液超声衰减谱与声速谱进行实验研究。     

Heat transfer characteristics of liquid-solid suspension flow in a horizontal pipe

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration, The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to 78 μm. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.     

旋流泵内液固两相流场的CFD-PBM耦合计算

为获得旋流泵内更为符合物理真实的液固两相流动特征,在传统欧拉(Euler)双流体模型基础上加载群体平衡模型(PBM),以考虑实际存在的颗粒聚并、破碎等动力学行为,与CFD耦合计算了不同流量、颗粒粒径及浓度下的液固两相流场,分析了颗粒存在对泵外特性的影响规律。计算结果表明:从进口到出口,叶片背面附近颗粒粒径明显增大;在叶轮出口位置,同一半径上,从叶片工作面到背面附近存在粒径梯度;在外缘部,沿轴向形成粒径梯度。与Euler模型计算结果对比发现:加载PBM模型后,颗粒总体浓度分布特征存在差异;同一轴截面上,颗粒浓度在中心部的分布基本相同,而在中间和外缘部位置出现差异。PBM模型计算得到的泵扬程、效率曲线更接近于实验值,证明基于CFD-PBM耦合计算的预测精度更符合实际。     

颗粒性质对叶片圆盘泵叶轮内颗粒分布的影响

为研究颗粒性质对颗粒在叶片圆盘泵叶轮内分布规律的影响,将叶片圆盘泵叶轮分为无叶区和叶片区,采用多重参考坐标系法模拟流体在叶片区和无叶区内的流动。采用Eulerian多相流模型、RNG k-ε湍流模型与SIMPLEC算法,利用Fluent软件对叶片圆盘泵内固液两相湍流进行数值模拟。对不同直径、不同浓度及不同密度颗粒在叶轮叶片区和无叶区的分布及颗粒在叶轮表面分布规律进行分析。结果表明:颗粒密度和颗粒直径对颗粒分布影响较大,颗粒密度、粒径越大,颗粒越难被液相带动加速而处在液相相对速度较慢的无叶区,随着颗粒密度、粒径的增大,叶轮表面颗粒浓度分布变化趋缓;颗粒浓度对颗粒在无叶区和叶片区分布影响较小;叶片表面颗粒浓度大于轮盘表面颗粒浓度,从动轮上轮盘表面和叶片表面颗粒浓度要小于相应主动轮表面颗粒浓度。     

Phase discrimination and a high accuracy algorithm for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump

PIV technology is an efficient and powerful measurement method to investigate the characteristics of fluid flow field. But for PIV particle image post-processing, some problems still exit in two-phase particles discrimination and velocity field algorithm, especially for high-speed rotating centrifugal slurry pump. In this study, through summarization and comparison of the various phase discrimination methods, we proposed a two-phase identification method based on statistics of gray-scale level and particle size. The assessment of performance through experimental PIV images shows that a satisfying effect for particle identification. For high speed rotation of the impeller, a combination of adaptive cross-correlation window deformation algorithm and multistage grid subdivision is presented. The algorithm is applied to experimental PIV images of solid–liquid two-phase flow in a centrifugal slurry pump, the results show that the algorithm in the present study has less pseudo vector number and more matching particle pairs than those of fixed window and window translation methods, having the ability to remove pseudo vector efficiently. It confirmed that the algorithm proposed in the present study has good performance and reliability for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump.     

Experimental study on size-dependency of effective permittivity of particle-gas mixture with agglomeration

The effective medium approximation （EMA） theory is the basis of a capacitance sensor used for concentration measurementof a particulate solid flow, its measurementresultis independenton particle size. In existence ofparticle agglomeration or aggradation, however, it is found that the effective permittivity of a gas/solid mixture is de-pendent on particle size. In this paper, a parallel plate, differential capacitance sensor is utilized to investigate theinfluence of particle size on the effective permittivity of the mixture in such a case. Static experiments using threematerials including glass, limestone and quartz particles were carried out in an off-line manner. The volume fractionof particles being tested ranged from20×10^-6to 600×10^-6, while the particle size was between 3 and 100μm.Experimental results showthat the effective permittivity of a particle-gas mixture with particle agglomeration is largerthan that predicted by EMA and the smaller the particle size, the larger the effective permittivity. The experimentprocess and analysis results are discussed in detail in the paper.     

超声测沙仪研究

黄河水中含有大量泥沙是泥沙固体颗粒分散在液体中形成的混合物,称悬浮液.超声波在悬浮液的声速和声衰减系数不但取决于组成各相自身的性质和含量,而且受到相互之间相互作用的影响.悬浮液的声衰减分为三种主要类型:吸收衰减、散射衰减和扩散衰减.前两类衰减取决于媒质的特性,而后一类衰减则由声源特性而引起.影响超声波测量含沙量准确度的主要因素有:含沙浓度和粒径级配;浑水中气泡等杂质;温度变化等.采用超声衰减法测量含沙量,并利用超声波双频测量含沙平均粒径修正含沙量可有效提高测量精度.     

旋流泵内颗粒分布特性及对泵性能的影响

基于Eulerian多相流模型和RNG κ-ε两方程湍流模型对旋流泵内的液固两相流场进行了数值模拟,获得了不同粒径、浓度时泵内的颗粒分布特性及对泵性能的影响。研究结果表明:固体颗粒进入泵内后主要集中于无叶腔内,无叶腔中的颗粒分布以泵轴为中心呈现一定的轴对称分布,随着粒径的增大,颗粒在无叶腔内壁面聚集的更加明显,随着浓度的增大,颗粒在无叶腔内的分布规律几乎没有变化,随着流量的增大,无叶腔中心部分颗粒浓度几乎不变的区域扩大;在叶轮内,叶片工作面附近的颗粒浓度要大于叶片背面的;随着粒径及浓度的增大旋流泵的效率会降低,随着粒径的增大泵的扬程会降低。     

A modified cross-correlation algorithm for PIV image processing of particle-fluid two-phase flow

PIV (Particle Image Velocimetry) technique for flow field measurement has achieved popular self-identify through over ten years development, and its application range is becoming wider and wider. PIV post-processing techniques have a great influence on the success of particle-fluid two-phase flow field measurement and thus become a hot and difficult topic. In the present study, a Phase Respective Identification Algorithm (PRIA) is introduced to separate low-density solid particles or bubbles and high-density tracer particles from the PIV image of particle-fluid two-phase flow. PTV (Particle Tracking Velocimetry) technique is employed to calculate the velocity fields of low-density solid particles or bubbles. For the velocity fields of high-density solid particles or bubble phase and continuous phase traced by high-density smaller particles, based on the thought of wavelet transform and multi-resolution analysis and the theory of cross-correlation of image, a delaminated processing algorithm (MCCWM) is presented to conquer the limitation of conventional Fourier transform. The algorithm is firstly testified on synthetic two-phase flows, such as uniform steady flow, shearing flow and rotating flow, and the computational results from the simulated particle images are in reasonable agreement with the given simulated data. The algorithm is then applied to images of actual bubble-liquid two-phase flow and jet flow, and the results also confirmed that the algorithm proposed in the present study has good performance and reliability for post-processing PIV images of particle-fluid two-phase flow.