Effect of cationic surfactant addition on the drag reduction behaviour of anionic polymer solutions

Although extensive research work has been carried out on the drag reduction (DR) behaviour of polymers and surfactants alone, little progress has been made on the synergistic effects of combined polymers and surfactants. In this work, the interactions between drag‐reducing anionic polymer (copolymer of acrylamide and sodium acrylate, referred to as PAM) and drag‐reducing cationic surfactant (octadecyltrimethylammonium chloride, OTAC) are studied. Solutions are prepared using both deionised (DI) water and tap water. The measurement of the physical properties such as electrical conductivity and viscosity are used to determine the surfactant–polymer interactions. The addition of surfactant to the polymer solution has a significant effect on the properties of the system. The critical micelle concentration (CMC) of the mixed surfactant–polymer system is found to be different from that of the surfactant alone. With the addition of surfactant to a polymer solution, a substantial decrease in the viscosity occurs. The observed changes in the viscosity of mixed polymer–surfactant system are explained in terms of the changes in the extension of polymeric chains, resulting from polymer–surfactant interactions. The anionic PAM chains tend to collapse upon the addition of cationic OTAC. The pipeline flow behaviour of PAM/OTAC mixtures is found to be consistent with the bench scale results. The DR ability of PAM is reduced upon the addition of OTAC. At low concentrations of PAM, the effect of OTAC on the DR behaviour is more pronounced. The DR behaviour of polymer solutions is strongly influenced by the nature of water (DI or tap). © 2011 Canadian Society for Chemical Engineering     

Time‐series and extended Karhunen–Loève analysis of turbulent drag reduction in polymer solutions

Direct numerical simulations and statistical analysis techniques are used to study the drag‐reducing effect of polymer additives on turbulent channel flow in minimal domains. Additionally, a new formulation of Karhunen–Loève decomposition for viscoelastic flows is introduced, allowing the dominant features of the polymer stress fields to be characterized. In minimal channels, there are intervals of “active” and “hibernating” turbulence that display very different structural and energetic characteristics; the present work illustrates how the statistics of these intervals evolve over the entire range of drag reduction (DR) levels. The effect of viscoelasticity on minimal channel turbulence is twofold: first, it strongly suppresses the active turbulent dynamics that predominate in Newtonian flow and second, at sufficiently high Weissenberg number it stabilizes the dynamics of hibernating turbulence, allowing it to predominate in the maximum drag reduction regime. In this regime, the stress fluctuations become delocalized from the wall region, encompassing the entire flow domain. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1460–1475, 2014     

Adsorption of cationic/nonionic surfactant mixtures on polyester

Experiments were performed to characterize the adsorption of the cationic surfactant benzalkonium chloride (BZK) on polyester as well as measure the effect of the cationic surfactant on polyester surface charge. Additional studies were performed to examine the effect of adding nonionic surfactants on surface charge. In studies of adsorption of BZK on polyester, different behaviors were observed at pH values 6 and 10, with adsorption reaching a maximum at pH 10 but not at pH 6. In probing the zeta potential and isoelectric point (IEP) of polyester exposed to solutions composed of BZK (cationic surfactant) and an ethoxylated alcohol (nonionic surfactant), it was seen that the IEP could be shifted to higher pH levels by increasing the mole fraction of nonionic surfactant in a cationic/nonionic surfactant solution. A maximum in the IEP was obtained at a certain mole fraction for most cases. The shift in the IEP was hypothesized to be driven by increased deposition of the cationic, since the nonionic itself did not significantly change the IEP. The cooperative interactions between cationic and nonionic species were theorized to be driven not so much by attractive interactions, but other interactions, such as minimization of cationic charge repulsion.     

Characteristic time scales for predicting the scalar flux at a free surface in turbulent open‐channel flows

The purpose of this study is to predict the turbulent scalar flux at a free surface subject to a fully developed turbulent flow based on a hydrodynamic analysis of turbulence in the region close to the free surface. The effect of the Reynolds number on turbulent scalar transfer mechanisms is extensively examined. A direct numerical simulation technique is applied to achieve the purpose. The surface‐renewal approximation is used to correlate the free‐surface hydrodynamics and scalar transport at the free surface. Two types of characteristic time scales have been examined for predicting turbulent scalar flux. One is the time scale derived from the characteristic length and velocity scale at the free surface. The other is the reciprocal of the root‐mean‐square surface divergence. The results of this study show that scalar transport at the free surface can be predicted successfully using these time scales based on the concept of the surface‐renewal approximation. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

Direct numerical simulation of the turbulent flow in a baffled tank driven by a Rushton turbine

We present a direct numerical simulation (DNS) of the turbulent flow in a baffled tank driven by by a Rushton turbine. The DNS is compared to a Large Eddy Simulation (LES), a Reynolds Averaged Navier‐Stokes (RANS) simulation, Laser Doppler Velocimetry data, and Particle Image Velocimetry data from the literature. By Reynolds averaging the DNS‐data, we validate the turbulent viscosity hypothesis by demonstrating strong alignment between the Reynolds stress and the mean strain rate. Although the turbulent viscosity ν_T in the DNS is larger than in the RANS simulation, the turbulent viscosity parameter C_μ = ν_T?/k², is an order of magnitude smaller than the standard 0.09 value of the k‐? model. By filtering the DNS‐data, we show that the Smagorinsky constant C_S is uniformly distributed over the tank with C_S ≈ 0.1. Consequently, the dynamic Smagorisnky model does not improve the accuracy of the LES. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

Drag reduction and mechanical degradation in polymer solutions in flow

A list of conclusions from experimental studies of drag reduction (DR) and mechanucal degradation in flow (MDF) is made. A statistical-mechanical model of chain conformations developed by the author⁹ is used, and its consequences for DR and MDF established. Experimental findings are explained in terms of the model, including those considered to be puzzling and contrary to expectations. A relation between the extent of mechanical degradation and flow time is derived. The equation obtained for relative drag reduction in function of time reproduces perfectly the experimental data for polystyrene+toluene solutions reported by Hunston and Zakin¹². Some predictions from the present model have yet to be tested experimentally.     

Dynamic salinity-induced phase-inversion conductivity measurements used to characterize alcohol ethoxylate based surfactant/oil/water systems

Dynamic conductivity measurements proved to be an effective and rapid method to determine the optimal experimental conditions for a salinity-induced phase-inversion from surfactant/oil/water (SOW) systems consisting of nonionic surfactants, more specifically alcohol ethoxylates. This emerging methodology can be used as a rapid screening tool to determine the impact of alcohol ethoxylate surfactants in a SOW solution and was demonstrated to be not only repeatable, but highly comparable to the traditional static method, in which the solutions are added to flat bottom tubes and allowed to equilibrate at a given temperature for extended time periods. Given a set of experimental conditions (oil-type, temperature, etc.), these dynamic salinity-induced phase-inversion (Dy-SPI) conductivity measurements can be used to determine the optimal salinity (S*) for a given surfactant at a set concentration, as well as its characteristic curvature via a series of experiments with varying oil types. Additionally, Dy-SPI was used to confirm the previously observed inverse relationship between the concentration of an alcohol ethoxylate and S* under a given set of conditions. What makes this method so unique is the amount of time (30 min to 1 h) and the simplicity of the equipment needed for these Dy-SPI conductivity measurements, allowing for a rapid screening tool for these SOW parameters.     

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%。     

Surface remobilization of buoyancy-driven surfactant-laden drops at low reynolds and capillary numbers

It is well known that the terminal velocity of a drop settling in a viscous fluid is impacted by surface tension gradients. These gradients can develop because of nonuniform accumulation of surfactant on the surface as a result of a number of transport mechanisms. Here, a surfactant transport model based on a sorption-limited Frumkin framework is used to describe surfactant transport in the presence of both surface convection and diffusion at low Reynolds and capillary numbers. Constants characterizing surfactant transport in the Frumkin framework are experimentally determined and used to predict aqueous drop velocities with varying surfactant concentrations and volumes. Computation is carried out by satisfying equations governing mass, momentum, and interface species conservation. Experiments demonstrate qualitative and quantitative agreement between predicted and measured drop velocities. It is shown that surface remobilization explains some observed trends in measured velocity as the drop size decreases. © 2018 American Institute of Chemical Engineers AIChE J, 65: 294–304, 2019     

Drag reduction of aqueous suspensions of fine solid matter in pipe flows

It is well known that drag reduction properties of polymer solutions in pipe flows are classified into two categories, based on the relationship between the friction factor and the Reynolds number. The degree of drag reduction either increases with an increase in the Reynolds number or is independent of the Reynolds number. In the latter case, the drag reduction behavior is referred to as type B behavior. In this study, the pressure losses of aqueous suspensions of biofibers and graphene oxide flat particles in pipe flows were measured to clarify the effect of the shape of suspended fine solid matter on the friction factor. The experimental results demonstrated that the behavior of the friction factor corresponded with the type B behavior of drag reduction. The mean velocity profile in the range of the turbulent flow was also estimated from the friction factor data.     

基于“lock-in”效应的阳离子三联表面活性剂蠕虫状胶束流变性能

以三联阳离子表面活性剂双(2-羟基-二亚甲基醚)-α,ω,γ-三(十六烷基二甲基氯化铵)(16-4(OH)-16-4(OH)-16)在水杨酸钠(NaSal)及氯化钠(NaCl)作用下形成的蠕虫状胶束为研究对象,向该体系中增溶苯乙烯(S_t)引发聚合,探讨了聚合前后胶束溶液的流变性能。通过表观黏度法研究了16-4(OH)-16-4(OH)-16/NaSal/NaCl及十六烷基三甲基溴化铵(CTAB)/NaSal两种体系聚合后溶液的耐温(T)及耐剪切性,并利用流变测试对16-4(OH)-16-4(OH)-16/NaSal/NaCl体系增溶S_t聚合前后溶液性能进行了表征。结果表明:CTAB/NaSal胶束体系中S_t最佳增溶量为0.05 g,T=100℃或剪切90 min,聚合后溶液表观黏度(η_a)分别为66.9、15.5 mPa·s;而16-4(OH)-16-4(OH)-16/NaSal/NaCl胶束中S_t 最佳增溶量为0.10 g,T=100℃且连续剪切90 min后,聚合后溶液的η_a 始终维持在99.1 mPa·s,该体系聚合后稳态模量(G₀)高于未增溶S_t体系,由此说明蠕虫状胶束内S_t聚合物链可以产生对其微结构的“lock-in”效应。     

Physicochemical behavior of mixed surfactant systems: Petroleum sulfonate and lignosulfonate

The physicochemical properties of mixed polymeric surfactant systems were studied with different techniques. A binary system consisting of lignosulfonate and petroleum sulfonate and a ternary system consisting of two different lignosulfonates and petroleum sulfonate were studied with respect to phase behavior, interfacial tension, specific conductivity, and pH measurements. In addition, the original lignosulfonates were subjected to ion exchange from sodium to calcium or vice versa, and the effects were investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 860–865, 2003     

Influence of the boundary conditions on capillary flow dynamics and liquid distribution in a porous medium

After depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into the porous medium creating a wetted imprint. The flow within the porous medium does not cease once all the liquid is imbibed but continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and the influence of the boundary condition on the liquid distribution within the porous medium is investigated. The pores at the porous medium boundaries can be defined as open or closed pores, where an open pore is checked for the potential threshold condition for flow to take place. In contrast, the closed pore is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the pores at distinct porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction, ranging from constant to steadily decreasing, to the profile with a local maximum, are found numerically. It is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the flow principal direction, and changing the boundary type from open to closed allows the liquid distribution within the porous medium to be controlled. In addition to the liquid distribution, the influence of the boundary conditions on capillary pressure and relative permeability is investigated, where both parameters are not influenced by variation of the boundary condition types. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Reconstruction of large-scale flow structures in a stirred tank from limited sensor data

We combine reduced order modeling and system identification to reconstruct the temporal evolution of large-scale vortical structures behind the blades of a Rushton impeller. We performed direct numerical simulations at Reynolds number 600 and employed proper orthogonal decomposition (POD) to extract the dominant modes and their temporal coefficients. We then applied the identification algorithm, N4SID, to construct an estimator that captures the relation between the velocity signals at sensor points (input) and the POD coefficients (output). We show that the first pair of modes can be very well reconstructed using the velocity time signal from even a single sensor point. A larger number of points improves accuracy and robustness and also leads to better reconstruction for the second pair of POD modes. Application of the estimator derived at Re = 600 to the flows at Re = 500 and 700 shows that it is robust with respect to changes in operating conditions.     

A modified method to detect surface rheological behavior of mixed partially hydrolyzed polyacrylamide (HPAM)/surfactant systems

The visualization of monolayers at the air/water interface by Brewster Angle Microscope (BAM) was used to watch the movement of the domains of surfactant or surface‐active complexes without any adscititious probe materials, and to examine the changes in surface rheology of partially hydrolyzed polyacrylamide (HPAM)/surfactant systems. Clear indications of rheological properties at the air/water interface are obtained over substantial concentration regions of the HPAM/Sodium Dodecyl Benzene Sulfonate (SDBS) and HPAM/Triton X‐100/SDBS systems, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 704–706, 2000     

Propulsion efficiency of achiral microswimmers in viscoelastic polymer fluids

We report the effects of polymer size, concentration, and polymer fluid viscoelasticity on the propulsion kinematics of achiral microswimmers. Magnetically driven swimmer's step-out frequency, orientation angle, and propulsion efficiency are shown to be dependent on fluid microstructure, viscosity, and viscoelasticity. Additionally, by exploring the swimming dynamics of two geometrically distinct achiral structures, we observe differences in propulsion efficiencies of swimmers. Results indicate that larger four-bead swimmers are more efficiently propelled in fluids with significant elasticity in contrast to smaller 3-bead swimmers, which are able to use shear thinning behavior for efficient propulsion. Insights gained from these investigations will assist the development of future microswimmer designs and control strategies targeting applications in complex fluids.     

Wetting kinetics of polymer solutions and force‐based contact angles

The effect of the shear thinning behavior and elasticity of polymer solutions on the dynamic contact angles are investigated. Under dynamic conditions, the contact angle of a liquid on a solid surface changes significantly with the substrate velocity from its equilibrium value. The dynamic contact angles for polyethylene oxide (PEO) solutions of two molecular weights 3 × 10⁵ and 4 × 10⁶ have been measured using a polyethylene terephthalate (PET) plate. The three‐parameter Ellis model to fit the rheological data to obtain shear thinning power n, characteristic shear stress, and the zero‐shear viscosity is used. The theory indicates that dynamic contact angles follow power law in this instance instead of showing Newtonian behavior with zero‐shear viscosity when the shear thinning effects are considered. The elastic effect becomes important at larger polymer concentrations that reduces the dependence on capillary number, that is, reduces n keeping with the experiments. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2533–2541, 2016     

A new differential pressure flow meter for measurement of human breath flow: Simulation and experimental investigation

The development and performance characterization of a new differential pressure‐based flow meter for human breath measurements is presented in this article. The device, called a “Confined Pitot Tube,” is comprised of a pipe with an elliptically shaped expansion cavity located in the pipe center, and an elliptical disk inside the expansion cavity. The elliptical disk, named Pitot Tube, is exchangeable, and has different diameters, which are smaller than the diameter of the elliptical cavity. The gap between the disk and the cavity allows the flow of human breath to pass through. The disk causes an obstruction in the flow inside the pipe, but the elliptical cavity provides an expansion for the flow to circulate around the disk, decreasing the overall flow resistance. We characterize the new sensor flow experimentally and theoretically, using Comsol Multiphysics^® software with laminar and turbulent models. We also validate the sensor, using inhalation and exhalation tests and a reference method. © 2016 American Institute of Chemical Engineers AIChE J, 62: 956–964, 2016     

壁面微沟槽与表面活性剂耦合对管道中湍流减阻特性的影响

通过矩形管道压降实验研究了壁面微沟槽和表面活性剂的减阻性能及联合减阻的增益效果,用粒子成像测速仪分析了流场特性。实验所用的微沟槽为3种不同结构的顺流向V形沟槽,表面活性剂为十六烷基三甲基氯化胺(CTAC),水杨酸钠(NaSal)作为补偿离子。结果表明,壁面微沟槽和表面活性剂溶液均有减阻效果,二者耦合后减阻率进一步提升,最高减阻率为48.26%。微沟槽的减阻性能主要作用在近壁区,通过影响边界层平均流速、速度脉动强度和涡结构,减少表面活性剂的湍动能损耗。当超过表面活性剂的临界雷诺数后,沟槽尖端的高剪切力会加剧胶束结构分解。表面活性剂能抑制湍流涡的演变,扩大微沟槽有效减阻的雷诺数范围。