表面活性剂虫状胶束流体中颗粒沉降负尾迹模拟

颗粒在剪切稀释黏弹性表面活性剂形成的蠕虫状胶束流体中沉降时会产生负尾迹,负尾迹的形成对该种复杂流体与固体颗粒之间的相互作用具有重要影响。基于Giesekus本构方程,采用POLYFLOW软件模拟了黏弹性表面活性剂(Viscoelastic Surfactant, VES)蠕虫状胶束流体中单颗粒的沉降过程,分析了流体松弛时间和迁移因子对颗粒周围速度场及应力场的影响,重点研究了颗粒尾部速度负尾迹的产生原因及其对颗粒曳力的影响。结果表明,Giesekus本构方程能够描述VES流体的非线性剪切变稀行为和弹性导致的拉伸变形。流体弹性导致颗粒尾部产生较大的拉伸变形,剪切稀化和流体弹性的共同作用使颗粒尾部产生拉伸变形,导致负尾迹出现。表征流体弹性的De(黛博拉数)越大,流体拉伸黏度的Tr(特劳顿数)越小,负尾迹越长。负尾迹的出现使VES流体中颗粒所受曳力减小,沉降速度开始增加。模拟结果为此种流体的进一步应用提供了一定的研究基础。     

黏弹性双子表面活性剂压裂液的制备及性能评价

考察了阴离子双子表面活性剂SA系列及水杨酸钠对阳离子双子表面活性剂SC-18溶液黏弹性的影响。黏弹性表面活性剂的基础配方为:1%SA-12+1%SC-18+0.5%水杨酸钠。该压裂液体系可满足井温小于100℃的低渗透油藏的压裂改造。该压裂液具有较好的抗剪切能力,170s~(-1)下剪切2h后,黏度保留率大于80%;破胶后黏度小于5 mPa·s,表明该配方具备优异的破胶性能;破胶后均无残渣;石英砂在压裂液的沉降速度满足压裂液性能要求。     

缓蚀剂和无机盐对黏弹性表面活性剂流变性能的影响

针对黏弹性表面活性剂转向酸化和压裂液体系,研究了新型双聚喹啉季胺盐缓蚀剂与其相互作用,和不同盐溶液对其黏温性能的影响和机理。结果表明,作为转向酸液体系的黏弹性表面活性剂对缓蚀剂的缓蚀效率无影响,双聚喹啉季胺盐缓蚀剂降低黏弹性表面活性剂耐高温性。低浓度无机盐溶液对黏弹性表面活性剂黏度无影响,而高浓度二价盐盐溶液CaCl₂和MgCl₂可显著提高黏弹性表面活性剂溶液的耐高温性能。在高浓度CaCl₂的存在下,含季胺盐酸化缓蚀剂的黏弹性表面活性剂耐高温性提高。     

表面活性剂聚集体的流变性质

以流变学基础知识为出发点，系统综述了胶束、微乳液，溶致液晶（层状、六角状、立方状），囊泡、虫状胶束等表面活性剂聚集体的流变性质及其剪切诱导结构转变现象的研究现状，总结了自流变性质的特点和理论模型，对具有黏弹性的表面活性剂活性剂聚集体进行了较为详细的论述，胶束稀溶液和微乳液多为牛顿流体；溶致液晶为非牛顿流体，有应力服价值和较高的黏弹性，囊泡的弹性性质比较突出，；虫状胶束体系具有非线性黏弹性，易形成网络结构；层状液晶、囊泡和虫状胶束等结构在剪切作用下能发生变化。这些结论对指导表面活性剂的研究和应用有重要意义。     

具有高温流变学稳定的VES压裂液性能的分析研究

针对目前黏弹性表面活性剂压裂液耐温性不足、成本高的缺点,研制了双子阳离子表面活性剂FL-25,并以其作为稠化剂配制成压裂液.FL-25无须添加任何有机或无机盐,便可在水中形成黏弹性流体.对新型双子阳离子表面活性剂的流变性质和热稳定性进行实验研究.结果表明:F-25溶液具有较好的稳定性、黏弹性、触变性和抗剪切性.在温度为110℃、剪切速率为170 s?1时,剪切90 min黏度保持在69 mPa·s,表现出良好的耐高温性能.     

三维小球随机堆积多孔介质内黏弹性流体流动数值模拟分析

复杂流体在多孔介质内的流动广泛存在于自然界和工业生产中,研究复杂流体的非牛顿特性对多孔介质内流动的影响具有重要的意义。基于黏弹性流体本构方程,对三维颗粒随机堆积的多孔介质模型进行研究,获得了流体流变性质对多孔介质内流动特性的影响规律。研究发现,流体的流变性质对多孔介质流场内流动的压力降和渗透率等有着显著的影响。对于黏弹性流体来说,随着弛豫时间的增大,即流体的弹性增强,导致流场内压力降减小,渗透率增大;当表征剪切稀化效应的迁移因子增大时流场内部压力降减小,渗透率增大。     

石油污染土壤地下水修复拖尾反弹及控制措施

在石油污染土壤地下水治理过程中,拖尾和回弹是修复难以达到预期目标的重要因素,导致修复时间延长和修复成本增加.表面活性剂增强修复(SER)在抑制石油污染土壤地下水修复治理拖尾反弹方面表现出色.分析了石油污染土壤地下水修复拖尾和反弹效应产生的原因,并介绍了拖尾和反弹效应的两项控制措施:使用表面活性剂泡沫和添加剪切稀化聚合物达到黏度控制效果,进而促进表面活性剂均匀分布,提高低渗透区的洗脱效率;表面活性剂增强原位化学氧化,有助于增强石油污染物的氧化降解,同时避免无二次污染.     

黏弹性表面活性剂压裂液的研究与应用进展

黏弹性表面活性剂压裂液是以黏弹性表面活性剂为主剂的清洁压裂液。黏弹性表面活性剂压裂液体系具有破胶后无残渣、携砂性好、滤失控制性能好等特点,但随着对环保问题的日益重视及钻井深度的不断增加,丰富黏弹性表面活性剂压裂液体系迫在眉睫。本文介绍了黏弹性表面活性剂压裂液的发展和应用。根据压裂液配方不同,将其分为常规黏弹性表面活性剂压裂液和非常规新型黏弹性表面活性剂压裂液,总结了不同种类的黏弹性表面活性剂压裂液的组成、耐温耐剪切等性能及应用情况。分析表明,降低成本、研制简单的配制工艺是常规黏弹性表面活性剂压裂液的主要发展方向;在油田进行大规模实际应用及得到更完善的体系是非常规新型黏弹性表面活性剂压裂液的主要发展方向。     

剪切稀化流体中微粒子聚集行为研究

在化工过程、生物工程等领域中,实现颗粒分离至关重要。通过整合微流控技术、高速显微图像采集技术和数字图像处理技术,探究微粒尺寸、通道流量和液相流变特性对微粒聚集的影响规律。结果表明,在剪切稀化流体羧甲基纤维素钠(CMC)水溶液中,随着通道流量和颗粒粒径增大,微颗粒聚集位置逐渐向剪切速率较高的一侧偏移;随着CMC质量分数增加,聚集位置不断向剪切速率较低的一侧偏移。利用求解的幂律型剪切稀化流体速度和剪切速率方程,结合对微颗粒的受力分析,证明稠度系数越大,聚集位置越偏向剪切速率较低处;剪切稀化特性越强,聚集位置越偏向剪切速率较高处,说明在幂律型剪切稀化流体中的黏度变化是微颗粒发生特殊迁移聚集行为的一个重要原因。     

新型缔合聚合物ADH溶液性能研究

研究了疏水缔合水溶性聚合物稀溶液的盐增粘性、抗温性、pH值效应,分析了溶液中聚合物与外加表面活性剂的相互作用,并初步研究了剪切速率对聚合物溶液粘度的影响。     

Numerical Characterization of the Bubble Rise Behavior in Viscoelastic Liquids

The bubble rise behavior in viscoelastic media is analyzed numerically with CFD. Three different constitutive models, Giesekus, linear and exponential Phan‐Thien‐Tanner, are used to evaluate three different biopolymer solutions. The terminal rise velocity over a range of bubble sizes is validated against experimental data. The local velocity fields are compared with respect to the shape and onset of the negative wake. Furthermore, the normal and shear components of the stress fields, transformed according to the local flow direction, are given. The simulations are performed with a volume of fluid solver in OpenFOAM.     

Extensional flow of wormlike micellar solutions

We consider the inhomogeneous extensional response of a new constitutive model, the VCM model [Vasquez, et al., 2007. A network scission model for wormlike micellar solutions I: model formulation and homogeneous flow predictions. J. Non-Newt. Fluid Mech. 144, 122-139] that has been developed to describe concentrated solutions of wormlike micelles. The time dependent numerical analysis is carried out in a simplified slender filament formulation appropriate for transient elongational flows of complex fluids. The simulations show that, beyond a critical extension rate, elongating filaments of a micellar fluid described by the VCM model exhibit a dramatic and sudden rupture event as a result of the scission of the entangled wormlike chains. The computations capture many of the features of the high-speed rupture process observed experimentally [Bhardwaj, et al., 2007. Filament stretching and capillary breakup extensional rheometry measurements of viscoelastic wormlike micelle solutions. J. Rheol. 51, 693-719] in filament stretching experiments with wormlike micelle solutions. The highly localized rupture predicted by the VCM model and the corresponding evolution in the tensile force within the filament is contrasted with the familiar and more gradual necking responses predicted by the upper convected Maxwell and Giesekus models under equivalent kinematic boundary conditions.     

Origin of the negative wake behind a bubble rising in non-Newtonian fluids

The present work aims at understanding the behavior of individual bubbles in non-Newtonian fluids. By means of a Particle Image Velocimetry (PIV) device, the complete flow field around either a single non-spherical bubble rising in polyacrylamide (PAAm) solutions or a solid sphere settling down in the same fluids shows for the first time the similar coexistence of three distinct zones: a central downward flow behind the bubble or the sphere (negative wake), a conical upward flow surrounding the negative wake zone, and an upward flow zone in front of the bubble or the sphere. This excludes then the possible influence of the interface deformation on the negative wake. A theoretical lattice Boltzmann scheme coupled to a sixth-order Maxwell model was developed for computing the complex flow field around a solid sphere. The good agreement with the experimental measurements provides evidence that the physical mechanism responsible for the negative wake in such fluids could be related to the fluid's viscoelastic properties.     

Characterization of viscoelastic fluid flow in a periodically driven cavity: Flow structure,frequency response,and phase lag

Transport phenomena in periodically driven cavities are important because of their relevance in polymer processing and microfluidics. The transient periodic flow of viscoelastic fluids in a cuboidal cavity, with periodic motion of top plate, was studied in this work. Flow with a characteristic time scale was achieved through the simple harmonic motion of the top plate. The flow in the cavity was characterized by measuring planar velocity fields using particle image velocimetry (PIV). Temporal variation of velocity except at central vertical plane showed predominance of the plate frequency. The temporal point variations, though seemingly similar to those for Newtonian and purely viscous non‐Newtonian fluids, led to rich varieties of spatial flow structures in case of the viscoelastic fluids. The overall flow behavior was characterized using spatial variations, phase trajectories, and streamline patterns. The transition from low Reynolds number steady‐lid driven type flow to complex vortical patterned flow was observed during a cycle of periodic motion of viscoelastic fluids. The effects of elasticity and inertia on the flow fields were analyzed. Computational fluid dynamics simulations with purely viscous shear thinning fluid (power law) and Newtonian fluid showed significant differences with experimental measurements on viscoelastic fluids. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

特征时间对剪切稀化流体气泡上浮特性的影响

非牛顿气液两相流广泛存在于工农业生产中,气泡和液相间的接触非常复杂,对相间的传递效率具有重要的影响。为了理解气泡在非牛顿流体中的运动特性,基于连续表面张力模型与Carreau本构模型,本文运用volume of fluid（VOF）法研究了单气泡在剪切稀化流体内自由上浮的运动特性。研究发现：气泡的动力学特性与液相的特征时间λ密切相关,液相的剪切稀化程度越强（流变指数n越小）或表面张力越小（Eo数越大）时,特征时间λ对气泡变形和尾涡的影响越大。在给定的剪切稀化程度和表面张力下,λ越大,气泡终端速度越大,其尾涡强度和尺度也越大,导致气泡周围液相高剪切速率区和低表观黏度区的范围越宽。此外,当液相的表面张力较小时,在气泡尾部出现了黏度盲区;并且随着λ的增大,黏度盲区逐渐脱离气泡尾部并破碎;黏度盲区的出现减小了气泡周围液相低表观黏度区的面积,增大了气泡上浮过程的摩擦阻力,降低了气泡的终端速度。     

聚合物流动的多尺度模拟

基于聚合物分子运动论,提出了一种新的计算聚合物流体的多尺度方法。该方法在宏观尺度上应用无网格方法求解速度场,在微观尺度上应用随机模拟技术计算聚合物对应力的贡献,从而避免需要本构方程来封闭连续性方程和动量守恒方程。对Hooke哑铃模型、FENE哑铃模型、FENE-P哑铃模型,模拟了突然起动平面Couette流动;对Hooke哑铃模型,模拟了方腔驱动流动。从而验证了该方法的有效性和计算结果的可靠性。     

A new fluid model for particles settling in a viscoplastic fluid

The study of the settling behaviour of particles in viscoplastic fluids is closely related to the study of rheology. In this paper, a thorough examination of the flow behaviour of viscoplastic fluids, in the form of aqueous polyacrylamide solutions, has been presented. The results of this study suggest that the experimental fluids exhibit time-dependent flow characteristics, where the apparent viscosity of the solutions depends highly on their shear history. This time dependency has been attributed towards the processes of destruction and rejuvenation in the ‘structural network’ of the fluids (due to the presence of hydrogen bonding between polyacrylamide and water molecules), as they are subjected to changing rates of shear. A new fluid model was thus developed to capture this flow behaviour. This model, termed as ‘semi-viscoplastic’, features temporary yield stress characteristics that tend to dissipate once the structural network of the fluid is destroyed due to the application of shear. The time dependency of the fluid viscous parameters becomes apparent in the settling sphere experiment, where it has been demonstrated that a sphere that is following the flow path of another sphere tends to attain a fall velocity that is significantly higher than the preceding sphere. Based on this finding, a new generalised correlation has been developed, through which predictions of the fall velocity of spherical particles settling through viscoplastic fluids, of various shear history, can be made.     

黏弹性流体基纳米流体流变学特性

黏弹性流体基纳米流体（viscoelastic fluid based nanofluid,VFBN）是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10^-3、5×10^-3、1×10^-2三种质量分数的十六烷基三甲基氯化铵/水杨酸钠水溶液为基液,粒子体积分数为0.1%、0.25%、0.5%、1.0%的铜纳米流体的剪切黏度、零剪切黏度以及松弛时间的测量,实验结果表明VFBN有明显的剪切稀变特性,同时纳米粒子的添加增大了基液的零剪切黏度,并导致基液黏弹性增强。以Giesekus本构模型为理论基础,利用实验参数得到了描述VFBN剪切黏度的实验关联式。     

Numerical simulation of viscoelastic two-phase flows using openFOAM

In this work a new solver is developed for the OpenFOAM^® CFD toolbox, which handles viscoelastic two-phase flows. A derivative of the volume-of-fluid (VoF) methodology is used to describe the interface. Established constitutive equations derived from kinetic theory, such as Oldroyd-B, Giesekus, FENE-P and FENE-CR, from network theory of concentrated solutions and melts, such as linear and exponential Phan-Thien–Tanner (PTT), and from reptation theory, such as Pom–Pom and XPP models, as well as multi-mode formulations are implemented in OpenFOAM. Validation of the numerical technique is performed by comparing detailed simulation predictions to data from several experimental studies, numerical studies and analytical models found in the literature. Two well-known viscoelastic free-surface effects, namely the Weissenberg and the Die Swell effect, are simulated. Furthermore, transient and steady-state droplet flow in shear and elongational flows is examined.