多相泵设计方法初探

１引言由于多相泵输送的是气液两相混合介质,而且其中气或液的含量往往高于常规泵或压缩机的工作范围,所以多相泵应兼备压缩机和泵的性能,这使多相泵的设计成为一个难点。到目前为止,国外已开发研制出的多相泵主要有容积式和叶片式［１］,业已进入现场试验和工业化应用阶段,但离形成完整的设计方法还有一定距离,国内这方面的工作则刚刚起步。所以目前对于多相泵尚没有成熟的设计方法,还不能象清水泵那样,按给定的流量、扬程、转速等参数进行可靠的设计。在多相泵的设计中,人们关心的主要问题是：泵型选择、总体设计方案的确定、效…     

受迫内流吸收过程传热性能的实验研究

1引言气体吸收过程是吸收式能量系统最重要的能量与质量传递过程。传统的吸收方式为立式除膜和卧式喷淋、然而传统吸收器的热质传递效率不理想，体积庞大，难于实现紧凑式热交换和空气直接冷却吸收，在应用上受到一定的限制．为此我们提出一种更为有效的新型气体吸收方式一管内受迫流动吸收。受迫内流气体吸收是一多组分多相流动传热传质过程，由于在汽液两相流动过程中，两相物质在流动过程中相互作用、充分混合，造成强烈的界面紊动，从而造成吸收边界层和传热边界层的亲动和两相间的频繁交换，大大强化了热质传递效率。同时，过程中随着…     

新型涡旋多相泵原理及其工作过程研究

提出了一种新型涡旋式气液多相混输泵,通过构建变啮合间隙涡旋齿型线,使得所形成的压缩腔存在一条通向排出口的内泄漏卸压通道。构建了一种液相压缩卸荷的新方法,解决了容积式多相泵在混输较高含液率介质时易出现的压缩腔液击问题。介绍了新型涡旋多相泵的工作原理,得到了变啮合间隙涡旋齿型线的生成方法和型线方程,分析了工作腔容积和啮合间隙的变化规律。建立了涡旋多相泵工作过程中气液介质在伴有内泄漏时的增压过程热力模型,求解得到了工作过程中压力的变化规律。     

固-液相变糊状区的格子Boltzmann研究

为深入探讨固-液相变材料在相界面内(糊状区)的流动和传热对固-液相变过程的影响,本文基于"焓-多孔介质"模型,提出研究糊状区的"多相流-多孔介质"两区域复合模型,将糊状区的高含液率视为多相流区域,而低含液率区域视为多孔介质,采用格子Boltzmann方法对固-液相变糊状区的流动和传热过程进行研究.重点讨论了相变温度半径,不同高、低含液率区的分界点γ_(tr)对糊状区的发展、迁移以及对相变过程的影响.研究结果表明糊状区厚度随相变半径的增大而增加,进而影响相变过程中流动和换热;对比复合模型的不同高、低含液率分界点γ_(tr)时和单纯多孔介质模型时的糊状区的边界、流动和换热情况,表明将糊状区高液相率区采用多相流模型进行分析,可以正确反映出高含液率区域内固相微粒随液相流动的特性及其对相变过程的影响。     

基于几何重建的气液两相流孔隙尺度模拟

本文基于二维micro CT扫描图像进行数值重构得到三维多孔介质几何模型,采用Shan-Chen多相格子Boltzmann方法(LBM)建立适用不规则几何边界区域内气液两相流动数值模型,在此基础上对复杂多孔介质内的两相流动过程进行孔隙尺度模拟。结果表明,气-液两相流动受限于多孔介质的复杂孔隙结构,气液表面张力、壁面润湿特性以及进出口压差对两相流动特性将产生明显影响。     

自由汇流旋涡多相耦合输运演变机理

含自由液面的汇流旋涡抽吸演变中存在多相耦合、物质传输、能量剧烈交换等物理过程,其中所涉及的多相流体耦合输运机理是具有高度非线性特征的复杂动力学问题,多相黏滞耦合输运动力学建模与数值求解具有较高难度.针对上述问题,提出一种含自由液面的汇流旋涡多相耦合输运建模与求解方法.基于水平集-流体体积耦合(CLSVOF)计算方法,结合连续表面张力模型和可实现(k-ε)湍流模型,建立含自由液面的汇流旋涡多相耦合输运动力学模型;利用一种有效的体积修正方案来计算高速旋转多相流,保证流场质量守恒和无散度的速度场;结合相间耦合求解策略对多相流体分布与多相界面进行精确追踪.基于旋流场多特征物理变量,得到多相耦合界面动态演变与跨尺度涡团输运规律,揭示了多相耦合输运过程与压力脉动特性之间的相互作用机理.研究结果表明:多相耦合输运过程是流体介质过渡的关键状态,旋涡微团受到不同时空扰动模式在界面处形成层层螺纹波形;旋涡多相耦合输运过程随着水口尺度增大而增强,且耦合能量激波引起非线性压力脉动现象.研究结果可为旋涡输运机理、涡团跨尺度求解、流型追踪等方面的研究提供有益借鉴.     

面向渗流力学应用特征的预条件方法

渗流力学模型由多个偏微分方程非线性耦合而成。在不同的应用问题中,渗流力学问题的特性并不完全相同,相应的求解方法也不相同。本文以油气藏开发中的典型数学模型为例,介绍多孔介质中的多相多组分渗流力学方程的数学形式、应用特征以及其离散线性方程组的高效求解方法,特别是一些常用的预条件方法。此外,对标准算例进行适当的修改,对部分预条件方法的共享内存并行效率进行了测试。     

N-17000型凝汽器的热力性能的数值分析

采用具有分布阻力和分布质量汇的多孔介质模型,将凝汽器壳侧多相、多组分的复杂流动简化为单相蒸汽、空气双组分的理想气体二维流动,建立了凝汽器数值计算的模型。针对一个N-17000型凝汽器的管束设计,通过数值模拟评价了两种布管方案的优劣,并依据对计算结果的分析,在布管方案1的基础上提出了改进建议,结果表明可以明显提高凝汽器的热力性能。     

多组分介质低温相平衡的理论研究现状

多元混合工质的相平衡特性是复杂且重要的问题之一。文中综述了国内外多组分介质相平衡的理论研究现状,包括状态方程和混合规则的改进、活度系数模型的研究以及对特定体系计算方法的研究等。并总结了适用于低温下尤其是针对天然气组分的相平衡计算方法。     

时间推进方法计算气液两相流动

１前言对气液、气固、液固两相或多相流体混合流动的研究在许多领域都显得十分重要,相对气固流动的研究来说,人们对气液两相流动的研究更为薄弱．而工程实际的需要（例如海底石油天然气混输问题）又要求我们对这种复杂流动有进一步的认识．在数值求解不可压单相或多相流动的方法中,应用较广的是压力－速度校正法。时间推进法是解可压问题的主要方法。如果能将它应用到不可压问题中去,在编程、计算兼容性方面都有较大优势。针对时间推进法在解不可压问题时遇到的困难,文献出提出一种所谓的人工可压缩性方法。本文用这种方法尝试计算了叶…     

凝固前沿和气泡相互作用的大密度比格子玻尔兹曼方法模拟

建立了二维双组分两相流的大密度比格子玻尔兹曼方法 (lattice Boltzmann method, LBM)模型. 该模型基于改进的Shan-Chen伪势多相流LBM模型, 结合采用不同时间步长的方法, 实现密度比达800以上的气液两相流模拟. 为了对模型进行验证, 模拟了在不同气液相互作用系数和密度比条件下气泡内外压力差与其半径之间的关系, 其结果满足Laplace定律. 将所建立的大密度比LBM与介观尺度的元胞自动机(cellular automaton, CA)和有限差分法(FDM)相耦合, 用LBM模拟气液两相流, 用CA方法模拟固相生长, 用有限差分法模拟温度场, 采用LBM-CA-FDM耦合模型对定向凝固过程中凝固前沿的气泡与液-固界面之间的相互作用进行模拟研究. 结果表明, 绝热气泡的存在影响了温度场分布, 使得凝固前沿接近气泡时, 液-固界面凸起, 在不同的固相生长速度条件下, 出现凝固前沿淹没气泡或气泡脱离凝固前沿的不同情况, 模拟结果与实验结果符合良好. 关键词： 格子玻尔兹曼方法 元胞自动机 凝固 气泡     

High pressure vle in petroleum fluids: Acoustical and visual experimental determination. comparison with data deduced from a number of E.O.S.

Abstract

An apparatus for the measurement of ultrasonic velocity in liquids at high pressures (up to 90MPa) is briefly described. It was used to determine liquid-liquid transitions and vapour-liquid phase boundaries in synthetic mixtures and petroleum fluids. The experimental results were confirmed using a transparent sapphire high-pressure cell. The experimental vapour-liquid equilibria were compared to those calculated from cubic equations of state, in order to emphasize the practical limitations involved in predicting the bubble point of such mixtures.     

Cavitation bubble collapse in a vicinity of a liquid-liquid interface – Basic research into emulsification process

The initial motivation for the study was to gain deeper understanding into the background of emulsion preparation by ultrasound (cavitation). In our previous work (Perdih et al., 2019) we observed rich phenomena occurring near the liquid-liquid interface which was exposed to ultrasonic cavitation. Although numerous studies of bubble dynamics in different environments (presence of free surface, solid body, shear flow and even variable gravity field) exist, one can find almost no reports on the interaction of a bubble with a liquid-liquid interface. In the present work we conducted a number of experiments where single cavitation bubble dynamics was observed on each side of the oil-water interface. These were accompanied by corresponding simulations. We investigated the details of bubble interface interaction (deformation, penetration). As predicted, by the anisotropy parameter the bubble always jets toward the interface if it grows in the lighter liquid and correspondingly away from the interface if it is initiated inside the denser liquid. We extended the analysis to the relationships of various bubble characteristics and the anisotropy parameter.Finally, based on the present and our previous study (Perdih et al., 2019), we offer new insights into the physics of ultrasonic emulsification process.     

纳米尺度下气泡核化生长的分子动力学研究

采用分子动力学方法模拟纳米尺度下液体在固体壁面上发生核化沸腾的过程,主要研究壁面浸润性对气泡初始核化过程和气泡生长速率的影响以及固-液界面效应在液体核化沸腾的能量传递过程中所起到的作用.研究结果发现：壁面浸润性越强,气泡在固壁处越容易核化.该结果与经典核化理论中“疏水壁面易于产生气泡”的现象产生了明显的区别.其根本原因是在纳米尺度下,固-液界面热阻效应不能被忽略.一方面,在相同的壁温下,通过增强固-液相互作用,可以显著降低界面热阻,使得热量传递效率提高,导致靠近壁面处的流体温度升高,气泡核化等待时间缩短,有利于液体沸腾核化.另一方面,气泡的生长速率随着壁面浸润性的增强而明显升高.当气泡体积生长到一定程度时,会在壁面处形成气膜,从而导致壁面传热性能恶化.因此,通过壁面的热流密度呈现出先增大后减小的规律.     

Ions at helium interfaces

The boundaries between different phases of condensed helium provide an interesting testing ground for studying ions in a quantum matter matrix. Here we consider the simplest positive and negative ions in helium — snowballs and electron bubbles, respectively — being trapped at the liquid-liquid interface of phaseseparated³He–⁴He mixtures and at the liquid-solid interface of⁴He. A comparison of experimental results for the trapping with predictions of the snowball and the bubble models shows that the models are in qualitative accord with the observations, but disagree in detail. It is suggested to use such studies for refinements of the ion models. In addition multielectron bubbles (=mesoscopic ions) and electrons on helium films are briefly discussed.     

Viscosity destabilizes sonoluminescing bubbles

In single-bubble sonoluminescence (SBSL) microbubbles are trapped in a standing sound wave, typically in water or water-glycerol mixtures. However, in viscous liquids such as glycol, methylformamide, or sulphuric acid it is not possible to trap the bubble in a stable position. This is very peculiar as larger viscosity normally stabilizes the dynamics. Suslick and co-workers call this new mysterious state of SBSL "moving-SBSL." We identify the history force (a force nonlocal in time) as the origin of this destabilization and show that the instability is parametric. A force balance model quantitatively accounts for the observed quasiperiodic bubble trajectories.     

Numerical investigation of relationship between water contact angle and drag reduction ratio of superhydrophobic surfaces

This paper proposes a novel bubble model to analyze drag reduction. The relationship between the slip length and air bubble height is discussed. The numerical relationship between the surface contact angle and slip length is obtained using the solid-liquid contact ratio in the Cassie equation. The surface drag reduction ratio increases by 40% at low velocities when the solid liquid contact ratio decreases from 90% to 10%. An experimental setup to study liquid/solid friction drag is reported. The drag reduction ratio for the superhydrophobic surface tested experimentally is 30%–35% at low velocities. These results are similar to the simulation results obtained at low velocities.     

Calculation of Thermodynamic Parameters and Degree of Ionization of Nitrogen and Its Mixtures with Argon in Typical Single-Bubble Sonoluminescence Conditions

The results of numerical simulation of the behavior of a system consisting of a spherical bubble filled with nitrogen or its mixtures with argon and surrounding water under external influence typical of experimental study of single-bubble sonoluminescence are presented. Comparison of the results of calculations and experiments shows that gas heated at the bubble compression stage cannot be regarded as the only source of radiation. This circumstance requires the presence of other, basic, sources. In the polarization model, this is the channel of electrical breakdown in a liquid. Possible electrical effects accompanying the liquid?solid phase transformation in water near the moment of the maximum compression of the bubble are assumed.     

Closed-loop liquid-liquid equilibria and the global phase behaviour of binary mixtures involving hard-sphere + van der Waals interactions

Calculations of the critical properties of binary mixtures of components of equal size are reported using the Guggenheim equation of state. The calculations are used to determine the global phase diagram of binary mixtures. Type VI phase behaviour is predicted successfully indicating that closed-loop liquid-liquid equilibria can be obtained from hard-sphere + van der Waals interactions. Closed-loop liquid-liquid equilibria occur in the region of the global phase diagram characterized by moderately strong unlike interactions and components with very dissimilar critical temperatures. The Guggenheim equation can predict all experimentally known phase behaviour types. In addition, other hypothetical phase behaviour types are also predicted.     

气泡成核过程的格子Boltzmann方法模拟

利用精确差分格子Boltzmann模型探讨水在特定温度下的亚稳态及不稳定平衡态, 获得等温相变过程中形成气泡和液滴的条件, 模型预测结果与理论解符合良好. 在该等温模型的基础上耦合能量方程, 通过调节流体-壁面相互作用力获得不同的气泡与固壁间接触角, 从而建立了一种新的描述气液相变的格子Boltzmann理论模型. 利用该新模型模拟不同流体-壁面相互作用力下凹坑气泡成核过程, 再现了气泡成核过程中的三阶段特性; 探讨了接触角、曲率半径及气泡体积随气泡成核过程的变化关系, 获得了与文献结果定性符合的曲率-气泡体积关系曲线. 关键词： 格子Boltzmann方法 气泡成核过程 气液相变 接触角