同轴双通道气流式雾化喷嘴初次雾化过程

对同轴双通道气流式雾化喷嘴的初次雾化过程进行了实验研究,发现在初次雾化过程中,初始微小扰动经过一段距离（即未扰动长度）后,在液体射流表面发展成为可以观察到的不稳定波.当气速U_g超过一临界值（大约25 m·s^-1）时,在不稳定波的波峰附近,形成小的突起,这些突起迅速被拉成细长液丝,液丝进一步破裂成液滴,最终导致液体的初次雾化.同时得到不稳定波长λ_m与环隙通道出口气速U_g、中心通道出口水速U_L的关系为λ_m＝68.60 U^-0.79_gU^-0.24_L;未扰动长度L_u与气速U_g、水速U_L的关系为L_u＝783.8 U^-1.54_gU^-0.16_L.     

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。     

氧化铝悬浮液流变性能及空间位阻影响机制

聚合物空间稳定机制是陶瓷悬浮液稳定的主要方式。本文以聚合物空间稳定的氧化铝悬浮液为研究对象，通过流变性能测试，研究了悬浮液体积分数、聚合物含量、颗粒粒径对悬浮液弹性模量的影响规律。结果表明，稳态剪切和振荡剪切两种流变测试模式都证明了悬浮液存在明显的弹性特征。确定了对于聚合物稳定的氧化铝悬浮液，影响弹性模量的核心要素为颗粒表面间距，因为颗粒表面间距影响了吸附聚合物的压缩程度。增大悬浮液体积分数、减小颗粒粒径均是通过降低颗粒表面间距以及被压缩吸附层的厚度使系统弹性模量上升，表现为弹性变大，最终影响悬浮液的稳定性。     

黏弹性表面活性剂溶液中颗粒沉降特性研究

黏弹性表面活性剂溶液悬浮颗粒流广泛存在于自然界和工业生产中,黏弹性表面活性剂溶液的非线性流变性质及应力松弛效应对其中颗粒沉降有着显著影响。采用FENE-P和Giesekus黏弹性本构模型对表面活性剂溶液中颗粒沉降特性进行研究,发现两种本构模型不仅表现出剪切稀化,而且出现拉伸硬化。颗粒在沉降初期的不稳定性主要是由溶液自身的弹性效应引起,弹性效应越强,颗粒沉降速度不稳定性越强,而剪切稀化效应会减弱颗粒沉降速度的不稳定。颗粒沉降过程中在其尾部形成一个“负尾迹”,随着剪切稀化和拉伸硬化效应增强,负尾迹区增大,弹性效应增加,负尾迹增强,负尾迹区流体内部反向速度分布导致的表面活性剂溶液中微观胶束的拉伸断裂和重构可能是引起颗粒沉降速度持续波动的原因。     

水煤浆气流雾化的初次破裂特性

以水煤浆和空气作为实验介质,利用高速摄像仪对同轴双通道喷嘴水煤浆气流雾化的初次破裂过程进行了实验研究,重点考察了在喷嘴出口附近水煤浆的射流核心长度和振荡频率等特征。研究结果显示,实验中水煤浆的破裂模式为非轴对称雷利破裂模式,根据实验结果,得到了浆体的量纲1射流核心长度与气速和液速之间的关系式。雾化过程中浆滴的产生与水煤浆射流振荡有关,研究了其Strouhal数与Weber数和液体Reynolds数之间的关系。     

硅酸盐复合黏弹性驱油剂的研究与评价

使用黏弹性表面活性剂形成具有一定黏弹性的蠕虫状胶束,所需原料的浓度较高,成本较高,制约了黏弹性表面活性剂驱油剂在现场的应用。以液体硅酸钠、两性表面活性剂、纳米二氧化硅为原料,制备了在经济使用浓度下能够显著提高注入水黏度且具有优良驱油性能的黏弹性驱油剂。透射电镜表征结果表明,驱油剂在有效质量分数为0.3%条件下即可达到较高的黏度。调整液体硅酸钠、表面活性剂的有效质量分数为0.12%~0.20%,制备的驱油剂的黏度达到10~50 mPa·s。实验对比了常用聚合物与黏弹性驱油剂的驱油效果,结果显示黏弹性驱油剂的驱油效果几乎是聚合物的2倍。这项工作为开发新型高效驱油剂提供了新方法,也为驱油剂流变学研究提供了新思路。     

驱油用聚丙烯酰胺溶液界面特性研究

使用 TRACKR全自动液滴界面张力仪测量了不同试验条件下十二烷 /聚丙烯酰胺溶液界面扩大、缩小时的流变特征及界面张力 ,开发出了用以表征液膜强度的界面黏弹性 E的测量方法。在十二烷 /聚丙烯酰胺界面形成稳定的过程中界面 (扩张 )黏弹模量不断增加 ,并逐渐达到恒定 ,其中弹性成分所占比例远大于黏性成分即 E′>E″。考察的聚合物浓度范围为 5 0～ 2 0 0 0 mg/ L ,界面黏弹模量从 1 7.6提高到 3 0 .6m N·m-1。放置 3 d后的聚合物溶液界面黏弹模量保留率为 82 .8%。实验结果表明聚合物浓度变化对界面张力影响不显著。     

碱和聚合物类型对多元复合体系性质影响及其作用机理研究

近年来,随着新型聚合物和表面活性剂的出现,它们之间的配伍性直接影响多元复合体系的性质特征和应用效果。针对多元复合体系中碱、聚合物和表面活性剂之间相互依存和制约关系,笔者利用仪器检测和理论分析方法,研究了碱和聚合物类型对多元复合体系界面张力、黏度和流变性和黏弹性的影响及其作用机理。结果表明,"缔合型"聚合物对多元复合体系界面张力存在不利影响,多元复合体系黏度愈高,界面张力愈高。多元复合体系中碱不仅会引起结垢和乳化问题,而且对聚合物溶液的流变性和黏弹性带来不利影响。Stem双电层理论分析和扫描电镜观测结果表明,碱可以使聚合物分子链双电层厚度减小,分子线团蜷缩,黏弹性变差。因此,无碱二元复合体系开发与应用是今后多元复合驱油技术发展方向。     

黏弹性表面活性剂及其在油田中的应用

介绍了黏弹性表面活性剂溶液的性质，确定黏弹性表面活性剂性质的测试方法和实验手段，以及其内部微观结构和流变特性等方面的研究成果。当黏弹性表面活性剂溶液浓度增加到某一临界浓度时，球形胶束开始向蠕虫状胶束转变，溶液黏度突然增大，随着浓度的进一步增大，蠕虫状胶束快速生长、增长并形成线型柔性棒状胶束，柔性棒状胶束相互缠绕、粘附甚至融合，形成某种超分子三维网状结构，溶液黏度急剧增加，并表现出较强的黏弹性。概述了黏弹性表面活性剂在油田中的应用，特别是在压裂液、酸液、钻井液及提高采收率等方面的应用，指出了黏弹性表面活性剂广泛运用的前景和尚未解决的问题。     

黏弹性聚合物熔体多相成型界面不稳定的机理分析

基于动网格法和EVSS/SU等混合有限元技术，建立了黏弹性聚合物多相成型界面不稳定的数值模拟系统，模拟结果与Matsunaga的理论研究和Yamaguchi的实验研究结论相符合。通过研究流率、黏度和松弛时间（弹性）对界面不稳定的影响规律，发现在相应条件下流率、黏度和松弛时间都能使界面变得不稳定，而界面两侧第一法向应力差的阶跃是导致黏弹性界面不稳定的根本原因，进而揭示了黏弹性界面不稳定的机理，并对生产实践提出了若干指导原则。     

Threshold wavelength on filaments of complex fluids

The breakup into drops of complex-fluid filaments – usually jets of polymeric and surfactant solutions – plays a central role in many engineering applications ranging from crop spraying to food processing and propulsion systems. To assess the influence of interfacial perturbations in the breakup process, we followed the dynamics of the initial wavelength of surface instability on complex-fluid filaments using direct numerical simulation. We found a threshold wavelength at low Reynolds numbers corresponding to a change on the filament's configuration near breakup from large primary drops connected by slender liquid threads for wavelengths below the threshold to clearly defined satellite drops in between the primary drops for wavelengths larger than the threshold. We also found that shear-thinning effects, by reducing the viscous resistance to the Marangoni stress responsible for the formation of the satellites, cause the threshold to appear at shorter wavelengths.     

简单剪切流动中液滴断裂机理

The experimental results of the deformation and breakup of a single drop immersed in a Newtonian liquid and subjected to a constant shear rate which generated by counter rotating Couette apparatus were presented in this paper. From experimental observations, the breakup occurred by three mechanisms, namely, necking, end pinching, and capillary instability. Quantitative results for the deformation and breakup of drop are presented. The maximum diameter and Sauter mean diameter of daughter drops and capillary thread radius are linearly related to the inverse shear rate and independent of the initial drop size, the dimensionless wavelength which is the wavelength divided by the thread width at breakup is independent of the shear rate and initial drop size, and the deformation of threads follows a pseudo-affine deformation for Cai/Cac larger than 2.     

Growth and breakup of a wet agglomerate in a dry gas–solid fluidized bed

Using CFD‐DEM simulations, a wet agglomerate of particles was placed in a void region of a dry vigorously fluidized bed to understand how wet agglomerates grow or breakup and how liquid spreads when agglomerates interact with dry fluidized particles. In the CFD‐DEM model, cohesive and viscous forces arising from liquid bridges between particles were modeled, as well as a finite rate of liquid bridge filling. The liquid properties were varied between different simulations to vary Bond number (surface tension forces/gravitational forces) and Capillary number (viscous forces/surface tension forces) in the system. Resulting agglomerate behavior was divided into regimes of (i) the agglomerate breaking up, (ii) the agglomerate retaining its initial form, but not growing, and (iii) the agglomerate retaining its initial form and growing. Regimes were mapped based on Bo and Ca. Implications of agglomerate behavior on spreading of liquid to initially dry particles were investigated. This article identifies a new way to map agglomerate growth and breakup behavior based on Bo and Ca. In modeling both liquid forces and a finite rate of liquid transfer, it identifies the complex influence viscosity has on agglomeration by strengthening liquid bridges while slowing their formation. Viewing Ca as the ratio of bridge formation time to particle collision and separation time capture why agglomerates with high Ca struggle to grow. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2520–2527, 2017     

低速横流作用下液体射流初次破碎实验

基于专门搭建的射流破碎雾化实验平台,利用高速摄像可视化研究低速横流作用下不同气液量纲为1参数对液体射流初次破碎模式特征和射流穿透轨迹特征的影响规律。实验结果表明,低速横流作用下液体射流破碎存在柱状破碎和袋式破碎两种模式,其中柱状破碎又可以分为鼓包破碎和拱形破碎。从实验得到的液气动量通量比q和液体韦伯数We_j射流破碎模式图可以看出,液气动量通量比q和液体韦伯数We_j共同决定低速横流条件下射流破碎模式,不同破碎模式之间存在明显的过渡边界。结合液气动量通量比q、液体韦伯数We_j、液体雷诺数Re_j等量纲为1参数,拟合得到了射流穿透轨迹曲线对数形式公式,该公式能够很好地预测低速横流作用下液体射流穿透轨迹,其中液气动量通量比q是影响射流穿透轨迹的主要量纲为1参数。     

液丝破裂过程的VOF模拟

Study on pinching liquid filament in literature was reviewed. The breakup of liquid filaments under surface tension is governed by incompressible, two-dimensional (2-D), Navier-Stokes Equations. Surface tension was expressed via a CSF (continuous surface force) model that ensures robustness and accuracy. A new surface reconstruction scheme, alternative phase integration (API) scheme was proposed to solve the kinematic equation,and was compared with other three referential schemes. A general-purpose computer program has been developed for simulating transient, 2-D, incompressible fluid flows with free surface of complex topology. The transient behavior of breaking Newtonian liquid filaments under surface tension was simulated successfully using the developed program.The initial wave growth predicted using API-VOF (volume of fluid) scheme was in good agreement with Rayleigh‘‘s linear theory and one-dimensional (l-D) long-wave theory. Both long wave theory and two-dimensional (2-D) API-VOF model on fine meshes show that as time goes on, these waves pinch off large droplets separated by smaller satellite ones that decrease in size with decreasing wavelength. Self-similar structure during the breakup was found using 1-D and 2-D models, and three breakups were predicted for a typical case. The criterion of filament breaking predicted by the 2-D model is that the wavelength is longer than the circumference of a filament. The predicted sizes of main and satellite droplets were compared with published experimental measurements.     

Experimental research on breakup of 2D power law liquid film☆

On account of limited knowledge of the breakup of power law liquid film, the process of its disintegration and atomization was studied by using a planar liquid film. A linear stability analysis was adopted to predict the breakup characteristics of the power law film. The predicting formulas of stripping breakup length and diameter of ligament were put forward presently. Through high-speed photography and laser light sheet illumination, different breakup characteristics of flat power law film under different conditions were derived. The characteristic dimension of breakup regimes were defined and extracted. The effects of several parameters (injection pressure, ambient pressure, nozzle structure and fluid property) on the stripping breakup length and spray angle were investigated. The results revealed that increasing both the velocity of liquid film and the ambient pressure facilitated the breakup of film, reduced the stripping breakup length and enlarged the spray angle in different extents. The comparison between theoretical and experimental results was conducted to validate the feasibility of the linear stability theory.     

Self‐similar breakup of viscoelastic thread for droplet formation in flow‐focusing devices

The self‐similarity of the breakup of viscoelastic dispersed thread for droplet formation in flow‐focusing devices is investigated experimentally. A high‐speed camera is used to capture the evolution and angles of the cone‐shaped liquid‐liquid interface. The self‐similar profiles for the liquid‐liquid interface are obtained by normalizing the interface with the minimum width of the dispersed thread. The breakup of the dispersed thread transfers from a self‐similar power law scaling stage with an exponent of 0.36 to a self‐similar exponential scaling stage. The asymptotic cone angles prior to final breakup are consistent with the value of 125.5° and 151°, respectively. The viscoelasticity inhibits the development of finite‐time singularity for the breakup of the liquid‐liquid interface at microscale, similar to the capillary breakup at macroscale. The results demonstrate that the breakup of the viscoelastic dispersed thread for droplet formation exhibits self‐similarity at microscale. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

The Influence of the External Imprinted Flow Field on Capillary Instability Driven Jet Breakup

The breakup of a flowing liquid jet surrounded by a second flowing liquid is governed by capillary instabilities. These instabilities are caused by minor perturbations in the flow field that build up sinusoidal waves at the jet interface and eventually break it up. The phenomenon of such fatal wavelengths was described first by Lord Rayleigh and later extended by several authors to quiescent and flowing liquid‐liquid systems. The jet formation in a co‐flowing environment was only recently investigated. Originating from the forced breakup of liquid jets in air, this paper reports on the breakup mechanism of liquid jets surrounded by a fluid. By using different flow cells and consequently different flow profiles along the jet trajectory, the breakup mechanism given by the material and process parameters could be excited or suppressed. Two questions concerning droplet generation and the droplet size distribution are addressed: the suppression of the fatal wavelength in transient flow fields and the use of external flow fields to support the fatal wavelength.     

表面张力变化对含气泡液体射流破裂的影响

使用高速相机研究了表面张力变化对含气泡液体射流破裂过程的影响。通过改变表面活性剂浓度获得了不同表面张力的液体射流。实验发现当液体射流速度保持不变时,减小液体表面张力会增加射流破裂长度。表面活性剂一方面降低了液体动态表面张力,减小了射流表面不稳定波的增长率,增大了射流破裂长度;另一方面表面活性剂在射流表面的非均匀分布会产生Marangoni应力,促使液体向射流变形区运动,从而推迟了射流破裂的发生,增大了射流破裂长度。通过理论分析得到了液体射流破裂长度表达式。发现射流内部气泡会显著缩短含表面活性剂射流的破裂长度。通过气泡扰动射流速度和吸附表面活性剂的分析,揭示了内部气泡对含表面活性剂射流破裂的影响规律。     

CFD-PBM耦合模型模拟气液鼓泡床的通用性研究

通过对不同操作压力和不同液体性质气液鼓泡床的模拟值与实验数据进行对比，从而验证CFD-PBM耦合模型的通用性。结果表明，CFD-PBM耦合模型在加入了气泡破碎修正因子后，可以很好地预测压力对鼓泡床流体力学行为的影响趋势，当压力升高时，气含率显著升高。不同液体黏度和表面张力条件下CFD-PBM耦合模型的模拟结果与实验结果均吻合较好。随液体黏度增大，气泡破碎速率减小，气泡尺寸分布变宽，曳力显著下降，气含率随之降低。随表面张力减小，气泡破碎速率增大，气泡变小，气含率升高。CFD-PBM耦合模型具有很好的通用性，原因在于考虑了压力、液体黏度和表面张力对气泡聚并、破碎和气液相间作用力的影响。