Drag-reducing Cationic Surfactant Research Articles

Drag-reduction of a nonionic surfactant aqueous solution and its rheological characteristics

In order to develop turbulent drag-reducing technology by using an environmentally friendly additive in a water-transporting system, the drag reducing characteristics in a non-ionic surfactant (Oleyldimethylamineoxide, ODMAO) dilute aqueous solution flowing in a circular pipe of 5 mm diameter have been experimentally investigated with an air-driven fluid resistance test device. The rheological characteristics of the solution have also been examined by a rheometer with a cone-plate flow cell. The results show that the ODMAO solutions are drag-reducing when concentration is 400 ppm or higher, that the critical Reynolds number corresponding to the maximum drag reduction rate increases with both concentration and temperature, and that the maximum drag reduction rate can reach up to 70% in the straight pipe. At low shear rates, the shear viscosity of ODMAO solutions with a relatively high drag-reduction behaves similarly to Newtonian fluids; at above a certain critical shear rate, it is firstly shear-thickening, then shear-thinning. Such shear-rate-dependent characteristics of the shear viscosity are attributed to the different transitions of micellar network structure induced by different shear rates. Relaxation of shear stress after removing an applied constant shear rate at which the solution is in the SIS (shear-induced structure) state is found to be well expressed by a 2-step Maxwell model with a tail relaxation time much shorter than that for a drag-reducing cationic surfactant, which indicates that for the ODMAO solution, a viscoelasticity as strong as a drag-reducing cationic surfactant is not needed to realize turbulent drag-reduction.

Relaxation Behavior of a Drag-Reducing Cationic Surfactant Solution

Relaxation Behavior of a Drag-Reducing Cationic Surfactant Solution

Turbulent drag reduction in nonionic surfactant solutions

There are only a few studies on the drag-reducing effect of nonionic surfactant solutions which are nontoxic and biodegradable, while many investigations of cationic surfactant solutions have been performed so far. First, the drag-reducing effects of a nonionic surfactant (AROMOX), which mainly consisted of oleyldimethylamineoxide, was investigated by measuring the pressure drop in the pipe flow at solvent Reynolds numbers Re between 1000 and 60 000. Second, we investigated the drag-reducing effect of a nonionic surfactant on the turbulent boundary layer at momentum-thickness Reynolds numbers Reθ from 443 to 814 using two-component laser-Doppler velocimetry and particle image velocimetry systems. At the temperature of nonionic surfactant solutions, T=25 °C, the maximum drag reduction ratio for AROMOX 500 ppm was about 50%, in the boundary layer flow, although the drag reduction ratio was larger than 60% in pipe flow. Turbulence statistics and structures for AROMOX 500 ppm showed the behavior of typical drag-reducing flow such as suppression of turbulence and modification of near-wall vortices, but they were different from those of drag-reducing cationic surfactant solutions, in which bilayered structures of the fluctuating velocity vectors were observed in high activity.

Evaluation of the role of a cationic surfactant on the flow characteristics of fly ash slurry

Transportation of fly ash is a major problem in its efficient disposal. The main problem associated with fly ash transportation is that the particles settle down sooner than desired. The primary objective of this research is that not only the fly ash particles should remain floated till it reaches the end but also settle down after that. In this investigation the role of a drag-reducing cationic surfactant and a counter-ion has been evaluated to achieve the objectives. The experimental results show encouraging trends of surfactant helping fly ash particles to remain water-borne. The material exhibited Newtonian behavior. This paper describes these in term of shear rates, shear stress, temperature, concentration and viscosity. Rheological tests were conducted using Advanced Computerized Rheometer. Zeta potential was measured to test the stability of the colloidal fly ash particles using Malvern Zeta Sizer instrument. Surface tension was also measured to know the drag reduction behavior of the fly ash slurry by using Surface Tensiometer. The test results and flow diagrams were generated using Rheoplus software and are presented in this paper. Surfactant concentration of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5% by weight was mixed with equal amount of counter-ion and the slurry was prepared by adding fly ash with ordinary tap water to achieve the desired solid concentration of 20% (by weight).

0504 抵抗低減化界面活性剤溶液のマルチ構造に関する研究(OS5-1 非ニュートン流体の流動現象,オーガナイズドセッション)

Experimental study on the contribution from the surfactant structure to the shear stress characteristics of drag-reducing cationic surfactant solution has been performed. The contributions from each structure were estimated while the surfactant concentration and the counter-ion molar ratio to the surfactants were widely changed. From the results, it was found that the structure having shortest relaxation time well corresponds to the shear stress characteristics. Form the comparison with the drag reduction occurrence map, the shortest relaxation structure was concluded to be the main cause of drag reduction occurrence.

On the mitigation of erosion–corrosion of copper by a drag-reducing cationic surfactant in turbulent flow conditions using a rotating cage

Erosion–corrosion is a complex materials degradation mechanism involving the combined effects of mechanical erosion and electrochemical corrosion. It is known to be induced by high shear stresses in strong flows. One way to mitigate this phenomenon is to use additives reducing the turbulent Reynolds stresses. Oleyltrimethyl ammonium cationic surfactant and sodium salicylate as counter-ion known to form thread-like micelles behaving as drag reducers were tested in this work and successfully imaged by using AFM technique. A shear stress mapping in the rotating cage using an electrochemical method was implemented in the absence and in the presence of surfactant, showing drag reduction amounts up to 65%. In a second step, erosion corrosion of Cu in Na 2SO 4 0.1 M in the presence of small amounts of NaCl (1 mM) was investigated on Cu microelectrodes located at different positions on plastic coupons in the cage. The surfactant effect was found to be beneficial by preventing the removal of the pre-existing oxide films, otherwise observed in the absence of surfactant. Tests performed with benzotriazole known as a good corrosion inhibitor for Cu, could not prevent either the breaking of the oxide film in strong flow conditions.

Chemical and Rheological Characterization of Drag-Reducing Cationic Surfactant Systems

Surfactant drag-reducing additives are very promising for saving pumping energy in recirculation systems such as district heating and cooling systems because of their “self-repairability” after mechanical degradation compared to polymer drag-reducing additives, which degrade irreversibly. The effectiveness of cationic surfactant drag-reducing additives, as indicated by their effective drag-reduction temperatures and Reynolds number ranges, depends on the chemical structures and concentrations of the surfactants and counterions. In this paper, the effects of the surfactant (alkyl chain length, saturated/unsaturated chain, odd/even numbers of carbons, and surfactant headgroup) and counterion (size, polarity, etc.) chemical structures on surfactant drag reduction, as well as three physical properties postulated to be associated with surfactant drag reduction, are addressed. Shear-induced structure (SIS), viscoelasticity (in the forms of nonzero first normal stress difference, quick recoil, and stress oversho...

Surfactant-induced effects on turbulent swirling flows

We employ digital particle imaging velocimetry (DPIV) to investigate the influence of a drag reducing cationic surfactant additive, cetyltrimethyl-ammonium chloride (CTAC), on turbulent swirling flows generated in a cylindrical vessel either by a rotating disk or a rotating disk fitted with vertical flat blades. The largest concentration of CTAC used in this study (0.05 ≤ C ≤ 0.5 mmol/l) is an order of magnitude smaller than those used in experimental investigations of surfactant induced drag reduction in turbulent pipe/channel flows. Even for such dilute systems, a number of dramatic and intriguing effects are observed. In the case of disk-driven flow, it is shown that the surfactant has a non-monotonic influence on turbulence intensity: both radial and axial root mean square velocity fluctuations first increase with increasing surfactant concentration C, reach a maximum and decrease upon further increase in C. Moreover, the maximum intensity is attained at a concentration that is practically independent of the angular frequency Ω of the disk. For the flow driven by bladed impeller, the introduction of the surfactant leads to flow reversal at the impeller plane for low concentrations. Enhancement in the radial and azimuthal mean velocities is also observed. For relatively larger concentrations (=0.5 mmol/l), a mean flow field that consists of multiple transient mixing pockets emerges as Ω exceeds a critical value. Plausible mechanisms are proposed to explain these observations.

Effect of variations in counterion to surfactant ratio on rheology and microstructures of drag reducing cationic surfactant systems

Rheology, drag reduction and cryo-TEM experiments were performed on Arquad 16–50/NaSal and Ethoquad O/12/NaSal surfactant systems at different counterion-to-surfactant ratios and at constant low surfactant concentrations, 5 mM, appropriate for drag reduction. The molar ratio of counterion-to-surface was varied from 0.6 to 2.5. All the surfactant systems described here are viscoelastic and drag reducing. The viscoelasticity and drag reducing effectiveness increase with increase in counterion/surfactant ratio. Network are present in the solutions with high ratio, and they are viscoelastic. However, shear is needed to induce network formation for solutions at low ratio. Cryo-TEM images confirm the existence of thread-like micelles which form entanglement networks, and show that the micellar network becomes denser with increasing counterion/surfactant ratio in one surfactant series. Both increase in the counterion/surfactant ratio and increase in the shear rate result in shorter relaxation times.

Effect of Chemical Structure on Viscoelasticity and Extensional Viscosity of Drag-Reducing Cationic Surfactant Solutions

Drag reduction, shear and extensional rheometry, and cryogenic transmission electron microscopy (cryo-TEM) were used to study aqueous solutions of one cationic surfactant, Arquad 16-50 (5 mM), with three isomeric counterions, 2-, 3-, or 4-Cl-benzoate at 12.5 mM. Each isomer showed different types of rheological and drag reduction behavior and different micellar structures. The 4-Cl system showed good drag reduction, high apparent extensional viscosity, and a thread-like micellar network, while the 2-Cl system showed no drag reduction, low apparent extensional viscosity, and only spherical micelles. The 3-Cl system was drag reducing and had high extensional viscosities at 30 °C. However, at 20 °C, the 3-Cl solution precipitated at high shear or extensional rates, leading to loss of drag reduction and low apparent extensional viscosity. The 3-Cl at 20 °C showed threadlike structures in some pictures and vesicles in others, presumably because of variations in the level of shear the samples were subjected to ...

Evaluation of Micellar Overlapping Parameters for a Drag-Reducing Cationic Surfactant System: Light Scattering and Viscometry

The equilibrium micellar structure in a tris(2-hydroxyethyl)(tallowalkyl)ammonium acetate (TTAA)/sodium salicylate (NaSal) surfactant system has been studied using light scattering and low-shear viscometry methods. Scattered light intensity autocorrelation functions were measured and the hydrodynamic correlation lengths were obtained for solutions with surfactant concentrations ranging from 1 to 5 mM and NaSal/TTAA ratios from 0.6 to 5 at temperatures from 10 to 80 °C. From the temperature dependence of the hydrodynamic correlation length, the concentration, counterion/surfactant ratio, and temperature at which the free micelles begin to overlap were inferred. The overlapping surfactant concentration decreases with increasing counterion/surfactant ratio, and the overlapping ratio decreases with increasing surfactant concentration. The overlapping temperature increases with increasing surfactant concentration and counterion/surfactant ratio. “Zero shear rate” viscosities of these solutions at 25 °C were measured to estimate the overlapping concentrations, and the results are compared to light scattering results.

Effect of Metal Ions and Compounds on the Rheological Properties of a Drag-Reducing Cationic Surfactant Solution Exhibiting Shear-Induced Structure Formation

The effect of various metal ions and compounds on the viscoelasticity of a 12.5/5 mMsodium salicylate (NaSal)/tris(2-hydroxyethyl) tallowalkyl ammonium acetate (TTAA) surfactant solution has been studied phenomenologically. This solution normally exhibits shear-induced structure formation and strong drag reduction properties. The viscosity andN1buildup times under a constant shear rate increase monotonically with the concentration of added Zn(OH)2, Cu(OH)2, or Fe(OH)3. The magnitude ofN1and the viscosity do not change significantly with the addition of Zn(OH)2, but decrease dramatically with increasing Cu(OH)2, Cu2(OH)2CO3, and Fe(OH)3concentrations. The effect is believed to be due to adsorption on insoluble particulates and to reaction between copper compounds and NaSal. Mg2+and Cu2+do not change the steady-state viscosity andN1, whereas Na+, Zn2+, and Ca2+decrease these quantities significantly at low shear rates. The loss of viscoelasticity in the NaSal/TTAA solution due to Cu(OH)2and Cu2(OH)2CO3can be recovered, however, by adding the chelating agent ethylenediaminetetraacetate to the contaminated solution. The rheological results are consistent with drag reduction experiments. The results show that chemical contamination may be an important issue for drag-reducing cationic surfactant additives used in industrial applications where such contaminants are present.

The effects of salts on the rheological characteristics of a drag-reducing cationic surfactant solution with shear-induced micellar structures

The effect of the counterion salt sodium salicylate (Nasal) on the transient rheological properties of a drag-reducing surfactant system tris (2-hydroxyethyl) tallowalkyl ammonium acetate (TTAA) has been studied with both rheometric and rheo-optical methods. Three types of transient behavior for N1 and viscosity were identified in 5 mM TTAA solutions depending on the counterion concentration: induction and growth (below equimolar concentration); overshoot and growth (above equimolar concentration); and overshoot then plateau (at high concentrations of Nasal). The transient flow birefringence and orientation angle show trends similar to those of the viscosity and N1. The second type of transient behavior suggests a two-stage alignment and shear thickening process. The SIS buildup time from the quiescent state, the rebuilding time after a strong preshear, and the relaxation time were also obtained from N1 measurements, and show a maximum around equimolar conditions. The initial N1 and viscosity immediately after the flow startup, on the other hand, show a maximum around a ratio of 2.5 to 3 Nasal/TTAA. For solutions with a Nasal concentration in the ratio 1.5 to 3, the steady state values of N1 and viscosity do not show much variation with Nasal concentration over the shear rate range covered, however. The effect of an addition of sodium chloride (NaCI) to an equimolar Nasal/TTAA solution on the characteristic times and steady state values was also quantified. These rheological results provide us with tools to determine the optimal concentration ratio for practical drag reduction applications.

The behaviour of drag-reducing cationic surfactant solutions

The behaviour of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. Our surfactant systems contained rod-like micelles; they consisted of equimolar mixtures ofn-tetradecyltrimethylammonium bromide,n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. Shear viscosity measurements in laminar pipe and Couette flows show the occurrence of the so-called shear-induced state, where the viscosity increases and the surfactant solution becomes viscoelastic. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more “S-shaped” profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.