表面活性剂溶液与壁面纵向微沟槽协同减阻研究

采用直接数值模拟方法对表面活性剂溶液在不同尺寸宽肋矩形微沟槽通道内的湍流流动进行了数值模拟研究。结果表明表面活性剂溶液的减阻性能在合适尺寸的微沟槽通道内能进一步得到强化,同时微沟槽的最优减阻尺寸在表面活性剂溶液中也可以得到放大;表面活性剂溶液在微沟槽通道内的协同减阻强化效果是由微沟槽的“约束作用”和“尖峰作用”这两个主要因素相互博弈的结果。微沟槽尖峰处具有较高的剪切应力,槽谷内部剪切应力很小。当微沟槽能有效防止近壁湍流涡侵入槽谷内部,且又能对部分流向涡的展向运动起到较好的约束作用时,微沟槽将表现出减阻强化性能,反之则会出现增阻性能。微沟槽在槽谷内诱导的数量多、尺寸小且旋转强度弱的二次流向涡是其在表面活性剂溶液中能增大“约束作用”和发挥减阻强化性能的本质因素。     

湍流边界层内表面活性剂减阻特性研究

湍流主要通过边界层流体与壁面的摩擦引起的,因此,研究表面活性剂的流向上边界层内湍流减阻性非常有意义,通过压降和粒子图像测速法分别研究了质量分数为10×10~(-6),50×10~(-6)和100×10~(-6)下的表面活性剂溶液与水的压降、范宁系数、减阻率、平均速度、速度分布云图、雷诺应力、涡量和涡量分布云图,实验发现:在表面活性剂的壁面范宁系数要比水时壁面的范宁系数要小,在质量分数为50×10~(-6)时减阻效果最好,最大减阻率为20%。得出结论:表面活性剂的加入使湍流边界层的厚度增加,雷诺切应力减小,在靠近管道的中心处的涡量最小,随着远离管道的中心,涡量缓慢地增大,近壁区的涡量降低,表面活性剂的减阻溶液的涡量比水的涡量稍微大一点,说明主要抑制管道中心区域的湍流强度来降低阻力,从而达到减阻效果。     

表面活性剂溶液与壁面纵向微沟槽协同减阻研究

采用直接数值模拟方法对表面活性剂溶液在不同尺寸宽肋矩形微沟槽通道内的湍流流动进行了数值模拟研究。结果表明表面活性剂溶液的减阻性能在合适尺寸的微沟槽通道内能进一步得到强化,同时微沟槽的最优减阻尺寸在表面活性剂溶液中也可以得到放大;表面活性剂溶液在微沟槽通道内的协同减阻强化效果是由微沟槽的"约束作用"和"尖峰作用"这两个主要因素相互博弈的结果。微沟槽尖峰处具有较高的剪切应力,槽谷内部剪切应力很小。当微沟槽能有效防止近壁湍流涡侵入槽谷内部,且又能对部分流向涡的展向运动起到较好的约束作用时,微沟槽将表现出减阻强化性能,反之则会出现增阻性能。微沟槽在槽谷内诱导的数量多、尺寸小且旋转强度弱的二次流向涡是其在表面活性剂溶液中能增大"约束作用"和发挥减阻强化性能的本质因素。     

表面活性剂湍流减阻研究进展

表面活性剂较高分子聚合物在流体管道输运中具有可逆机械降解特性的优点,更适用于存在高剪切的场合以及封闭的循环回路进行减阻,但存在对其复杂流变特性及减阻机理认识不完善的问题,使得其在减阻领域的应用受到了限制。本文回顾了作者近年来在表面活性剂溶液微观结构、复杂流变学特性、湍流结构以及其与减阻和传热性能之间的内在联系方面的研究进展;介绍了表面活性剂减阻和壁面微沟槽协同作用减阻的研究成果;指出通过拉伸流的方式能够在压损较小的情况下更有效地提高表面活性剂溶液的传热性能。针对表面活性剂现有研究的不足,本文提出4条建议作为表面活性剂的未来研究方向,分别为开发环境友好型高效表面活性减阻剂、强化换热装置的优化设计及优化布置、表面活性剂与其他减阻方式耦合特性的深入研究以及表面活性剂在尺度放大、防腐和减阻持久性方面的实际工业应用研究。     

阳离子Gemini表面活性剂18-3-18/水杨酸钠胶束体系流变和减阻性能研究

为丰富和发展表面活性剂减阻体系,研究了阳离子Gemini表面活性剂丙撑基双(十八烷基二甲基氯化铵)(18-3-18)与水杨酸钠(NaSal)组成的新型胶束体系的流变和减阻性能。考察了不同浓度胶束体系的流变特性,讨论了该胶束体系的摩擦阻力系数和减阻率随广义雷诺数的变化关系,并比较了在光滑管及粗糙管中该体系的减阻效果。结果表明,18-3-18/NaSal胶束体系具有良好的黏弹性、触变性和剪切变稀性。随胶束体系浓度增大,减阻效果提高。对18-3-18/NaSal(5 mmol L 1/10 mmol L 1)胶束减阻体系,存在临界广义雷诺数,最大减阻率为78.5%;对18-3-18/NaSal(7.5mmol L 1/15 mmol L 1,10 mmol L 1/20 mmol L 1)胶束体系在光滑管中的最大减阻率可分别达到82.3%和81.7%。该胶束体系在光滑管中的减阻效果优于粗糙管中的减阻效果,表明18-3-18/NaSal胶束是一种新型减阻胶束体系。     

非光滑结构对轮胎抗水滑性能的影响

以轮胎单个花纹沟作为分析对象,建立V形沟槽分布数学模型和轮胎水滑模型,运用计算流体力学方法对轮胎水滑性能进行分析。用正交试验法分析和对比V形沟槽结构与光滑结构的壁面减阻率,得到减阻效果最佳的V形沟槽设计参数,并引入轮胎纵向花纹沟槽底部进行水滑分析。结果表明,V形沟槽非光滑结构能有效降低轮胎花纹沟壁面阻力系数,提高轮胎的抗水滑性能。     

低粘附功管壁的内流减阻研究

以乙烯基三乙氧基硅烷 无水乙醚溶液处理玻璃管道内壁 ,降低流体水与管壁间的粘附功 ,研究了低粘附功内壁管道的内流减阻性能。结果表明 ,在管壁与液体间的粘附功小于液体的内聚功条件下 ,当雷诺数大于临界雷诺数时 ,低粘附功内壁管道呈现明显的内流减阻效果 ,临界雷诺数的值与一定的临界壁面剪力值或层流底层临界厚度值相对应 ;在减阻区内 ,减阻率随雷诺数的增加及管道内径的减小而增大 ,阻力系数的无因次关联式可表示为λ=f (Re ,X) ,其中X为无因次数群 [W / (du2 ρ) ]。     

减阻表面活性剂的研究进展

介绍了表面活性剂减阻的机理。探讨了影响表面活性剂减阻效果的各种因素,包括:表面活性剂与补偿离子的结构及其浓度、管路系统的直径、流体的温度和速度以及环境中的金属离子。论述了表面活性剂的减阻与传热效率之间的关系;并且讨论了在使用减阻表面活性剂的循环系统中提高传热效率的方法。总结了减阻表面活性剂的一般特点。预测了减阻表面活性剂的发展趋势。引用文献35篇。     

二氧化硅疏水涂层的水下减阻性能研究

采用溶胶-凝胶法中的Werner StÖber方法制备二氧化硅颗粒,并添加于聚偏二氟乙烯中,喷涂在钢片表面,制得类似荷叶表面结构的疏水涂层。红外光谱测试结果显示,制备的二氧化硅颗粒纯度较高,副产物少。X射线衍射结果表明,二氧化硅颗粒为无定形结构。疏水涂层表面的扫描电镜照片表明,表面颗粒形貌均一,分散性好,具有仿生微粗糙结构。测得涂层水接触角为133°。减阻测试结果表明,低雷诺数下,减阻率大大高于普通聚偏二氟乙烯树脂,最高可达57.6%。减阻效果受二氧化硅颗粒用量的影响,2.5 g聚偏二氟乙烯加入0.4 g二氧化硅时减阻效果较好。     

表面活性剂添加对歧管式微通道阻力特性的影响

歧管式微通道（MMC）热沉具有热阻小、结构紧凑、冷却液流量小、流速低、沿着流动方向温度分布均匀等优点,但其小尺寸所产生的较大压降却增加了泵功的损耗.本文研究了表面活性剂添加对其阻力特性的影响,实验选用了纯度为95%的阴离子表面活性剂十二烷基硫酸钠（SDS）和纯度为98%的新型绿色非离子表面活性剂烷基多糖苷（APG）作为减阻添加剂,浓度分别为100和300 mg·kg^-1,结果表明阻力减小率与流速和温度有关.在层流区内减阻效果不是特别明显;但是当流体进入紊流区后阻力减小率开始明显增大,尤其是进入充分发展的紊流区后减阻效果大大加强.此外,温度的提升也可增加阻力减小率,但添加SDS后减阻效果的改善却不及APG.通过对两种不同类型表面活性剂的实验比较,发现温度较高时APG比SDS具有更佳的减阻效果.     

幂律流体在Kenics型静态混合器中流动特性分析

为了探究Kenics型静态混合器内扭旋叶片剪切作用对幂律流体流动的影响,利用旋转流变仪测量了浓度为0.5wt%, 0.7wt%, 0.9wt%的羧甲基纤维素(CMC)水溶液的流变参数,采用数值模拟与实验研究了扭旋叶片作用下幂律流体流动阻力和剪切稀化特性。对流场研究表明,扭旋叶片诱导产生了内流涡旋、绕流涡旋和近壁面涡旋,有效强化了静态混合器内流体流动的剪切作用。受多个纵向涡旋分布的影响,扭旋叶片局域流场中周向45°位置速度最高,周向30°位置涡量与剪切应力最高而黏度最低。径向0.4倍半径位置速度最高,0.7倍半径位置黏度最高。静态混合器有效提高了流体的二次流流动速度和剪切应力,降低了幂律流体的黏度和流动阻力系数。     

Combined effects of temperature and Reynolds number on drag‐reducing characteristics of a cationic surfactant solution

The drag‐reducing characteristics in the turbulent channel flow of dilute cationic surfactant solution, cetyltrimethyl ammonium chloride (CTAC)/sodium salicylate (NaSal) aqueous solution, were experimentally investigated in a closed loop fluid flow facility at different temperatures. The mass concentrations of the surfactant solution ranged from 75 to 200 ppm, and the temperatures ranged from 15 to 55°C. The cationic surfactant solution showed a great drag‐reducing ability, which was greatly affected by concentration, temperature, and Reynolds number. It was found that there existed a critical temperature T_c in each solution at different concentrations. Above T_c, drag‐reduction level decreases and reaches the behaviour of water flow without drag‐reducing ability. A new temperature parameters T_f, was proposed, and the difference between T_c and T_f can represent the effective temperature range for the drag reduction at a certain Reynolds number. The variation tendency of T_f and T_c with Reynolds numbers can give the guidance of selecting effective drag reduction range to the practical application in the district heating systems (DHS). It was supposed that temperature and shear stress are two kind of energy applied on the surfactant microstructure, which can be helpful to the surfactant network formation or dissociation depending on their values. © 2011 Canadian Society for Chemical Engineering     

Direct numerical simulation of surfactant solution flow in the wide‐rib rectangular grooved channel

The turbulent flow of surfactant solution in the wide‐rib rectangular grooved channels was studied by direct numerical simulation. Moreover, the variations of near‐wall streamwise vortices with time were discussed and the distributions of streamwise vortex radius, swirling strength and density were quantitatively investigated. It was found that the influence of microgrooves on the fluid mainly occurred within the buffer layer and microgrooves could induce numerous streamwise vortices with small size and swirling strength within the grooved valleys. The drag‐reducing enhancement mechanism of microgroove in the surfactant solution could be mainly considered as the competing results between the “restriction effect” and “tip effect” of microgroove, and the essential factor should be the numerous secondary streamwise vortices with small size and swirling strength within the grooved valleys. Furthermore, a predicted method for the optimal drag‐reducing size of microgroove was proposed, and the prediction values agreed well with the numerical results. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2898–2912, 2018     

阳离子型表面活性剂与聚合物复配体系协同减阻作用

为探究阳离子型表面活性剂和聚合物复配体系的协同减阻作用,以阳离子型表面活性剂十六烷基三甲基氯化铵（CTAC）和聚合物聚丙烯酰胺（PAM）为研究对象,设计搭建多功能湍流减阻实验测试装置,实验分析聚合物离子类型对复配体系协同减阻的影响,优选复配体系,进一步研究复配体系协同减阻作用随表面活性剂浓度、聚合物浓度、温度的变化规律。实验结果表明：CPAM-CTAC/NaSal复配体系协同减阻作用>AmPAM-CTAC/NaSal复配体系协同减阻作用>NPAM-CTAC/NaSal复配体系协同减阻作用>APAM-CTAC/NaSal复配体系协同减阻作用。CPAM-CTAC/NaSal复配体系的协同减阻作用在CTAC/NaSal浓度达到聚合物饱和浓度（PSP）0.3g/L时到达顶峰,平均减阻效率高达69.22%;当CTAC/NaSal浓度增加至0.5g/L后,平均减阻率迅速减小至10.08%,复配体系的临界广义雷诺数亦迅速降至7535.20,抗剪切性减弱。随着CPAM浓度由0.05g/L增加到0.2g/L,减阻破坏区减阻率可由9.08%增加至57.49%,临界广义雷诺数由31272.43增加到45033.36,抗剪切性增强;当CPAM浓度超过第二临界缔合浓度（CAC Ⅱ）0.15g/L后,减阻破坏区减阻率增加趋势及抗剪切性增强趋势均变缓。此外,相较于单一减阻剂,复配体系耐温性显著增强,55℃时最大减阻率增至69.05%。     

Wavelet autocorrelation identification of the turbulent flow multi-scales for drag reduction process in microbubbly flows

Measurement of turbulent flow was performed in a fully developed channel flow for both single-phase and microbubble injection conditions. A drag reduction was achieved by microbubble injection in the boundary layer. Further understanding of this phenomenon has a significant impact on energy saving. In this experiment, the Reynolds number was 5128 based on the half height of the channel. The particle image velocimetry (PIV) technique was used to obtain two-dimensional full-field velocity components in the streamwise direction near-wall normal plane. Wavelet autocorrelations were applied to the streamwise fluctuating velocity fields. By applying wavelet analysis, many of the shortcomings of Fourier analysis were overcome. The comparison of the wavelet analysis results between single-phase flow and microbubble flow indicated that the microbubbles drag reduction is a multi-scale mode, in which the small-scale fluctuations are suppressed.     

Velocity measurements in turbulent flow of viscoelastic solutions

An experimental study, based on streak photograph determination of instantaneous velocities, was directed at determining the turbulent flow velocity profiles of polymer solutions in circular pipes. The measurements resolve several discrepancies in interpretation of earlier velocity profile measurements in drag reducing systems. In particular, it is shown for dilute drag reducers that the semilogarithmic profile due to Prandtl with the same slope as for Newtonian fluids is quantitatively correct provided Bogueés empirical correction function is applied to the data. For a relatively concentrated solution, data serve to extent on earlier study which has shown the flow to be transitional at surprisingly high values of Reynolds number.     

Numerical studies on effects of bubbles regular array on the liquid‐phase turbulence

It is well known that additive drag‐reducing methods have broadly developing prospects, so studies on mechanisms of additive drag reduction are very necessary. We hypothesised that the main reason for bubbles induced drag reduction is the modification on liquid‐phase turbulence structure by the addition of bubbles, and therefore such modification is the focus of our investigation. In this paper, effects of bubbles on liquid‐phase turbulence under the circumstance of regular bubble array were investigated by using Euler–Lagrange two‐way numerical simulations. The liquid‐phase velocity field was solved by using direct numerical simulations (DNS) in Euler frame of reference, and the bubble motion was tracked by using Newtonian motion equations that took into account interaction forces including drag force, shear lift force, gravity force, buoyant force, and inertia force in Lagrange frame of reference. The coupling between the phases was realised by regarding the interphase forces as momentum source terms of the continuous phase. Similarities and differences for effects of bubbles and surfactants on liquid turbulent flows were also analysed. The study indicated that addition of bubbles enhances the mean streamwise velocity, greatly reduces the Reynolds stress, and shows anisotropic suppression to the velocity fluctuations. The interphase force has a great influence on budget of energy balance. It is a gain term near the wall and is a loss term in a wide range of the channel core.