Drag-reducing Surfactant Solution Research Articles

Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow

An experimental study is performed to investigate the effects of the extensional rheological properties of drag-reducing wormlike micellar solutions on the vortex deformation and turbulence statistics in two-dimensional (2-D) turbulent flow. A self-standing 2-D turbulent flow was used as the experimental set-up, and the flow was observed through interference pattern monitoring and particle image velocimetry. Vortex shedding and turbulence statistics in the flow were affected by the formation of wormlike micelles and were enhanced by increasing the molar ratio of the counter-ion supplier to the surfactant, ξ, or by applying extensional stresses to the solution. In the 2-D turbulent flow, extensional and shear rates were applied to the fluids around a comb of equally spaced cylinders. This induced the formation of a structure made of wormlike micelles just behind the cylinder. The flow-induced structure influenced the velocity fields around the comb and the turbulence statistics. A characteristic increase in turbulent energy was observed, which decreased slowly downstream. The results implied that the characteristic modification of the 2-D turbulent flow of the drag-reducing surfactant solution was affected by the formation and slow relaxation of the flow-induced structure. The relaxation process of the flow-induced structure made of wormlike micelles was very different from that of the polymers.

Flow Characteristics of Drag-Reducing Surfactant Solutions

The objective of this study is to clarify the flow characteristics of drag-reducing flow and to elucidate the mechanism underlying this phenomenon. The surfactant and counter ion we used were Lipothoquad O/12 and sodium salicylate, respectively. The drag reduction rate (DR%) was measured by using a recirculating system with a diameter of 25.6 mm. We also measured the flow characteristics of the surfactant solutions with different concentrations and temperatures by using particle image velocimetry (PIV). From the experimental results, DR% at an average velocity of 2.0 m/s increased from 0 to 68% as the temperature increased from 10 to 40 °C at a constant concentration of surfactant (300 mg/L). From the velocity contour plot obtained from PIV, we found that the thickness of the lower-velocity region of the drag-reducing flow near the pipe wall was thick at 20 °C, whereas vortex motions seemed controlled at 30 °C. On the other hand, the lower-velocity region thickened as the concentration of the surfactant increased at 25°C. Even if the same level of drag-reducing effects occurred, the flow patterns were quite different depending on the concentration and temperature.

Rheological modeling of both shear-thickening and thinning behaviors through constitutive equations

Shear-thickening and thinning behaviors are often observed in the rheological measurements of dilute surfactant solutions with drag-reducing ability in wall-bounded turbulent flows. This study proposes a simple rheological modeling method based on combining constitutive equations, such as Giesekus and FENE-P models, with a fluidity equation to determine both thickening and thinning behaviors in simple shear flows simultaneously. The Giesekus and FENE-P models, which are typically used in numerical studies on turbulent drag reduction, cannot capture such complex behaviors. However, the proposed models, called f-Giesekus and f-FENE-P models, can predict the shear-thickening properties. The developed models are inspired by the Bautista–Manero–Puig model, where the Oldroyd-B model (upper-convected Maxwell model) is coupled with the fluidity equation. Parametric studies prove that the proposed models can accurately predict both the shear-thickening and shear-thinning properties. Notably, the f-FENE-P model shows prominent flexibility to determine the plateau region of the shear viscosity as a function of the shear rate. We verify that the analytical solutions of the f-FENE-P model agree with the experimental data of the shear viscosity in dilute drag-reducing surfactant solutions, except for the remarkable steep increase in the shear viscosity. The start-up shear flow is also studied to confirm various transitions accompanied by the overshoot and undershoot of the f-FENE-P model.

Experimental study on flow in cylindrical container of drag-reducing surfactant solution due to agitator

Experimental study on flow in cylindrical container of drag-reducing surfactant solution due to agitator

Exergy transfer characteristics analysis of turbulent heat transfer enhancement in surfactant solution

This paper presents an exergy transfer analysis for turbulent drag reducing surfactant solution flow with and without heat transfer enhancement devices which employ static or dynamic mixers. Heat transfer and pressure drop measurements were performed at an inlet temperature of 297.7–298.2 K in pipe flow with a concentric tube heat exchanger. The environmental temperature in the analysis was set to be 288.2 K in assumption of a cooling system. The experimental range of the Reynolds number was 1.0×104 to 4.2×104. Adding surfactant to a water flow decreases the exergy transfer Nusselt number, Nue, owing to the heat transfer reduction and increases the exergy transfer efficiency, ηeff, by a maximum of 9.3% at high Reynolds numbers at moderate fluid transport distance owing to the drag reduction. Also the secondary flow caused by the enhancement devices increases Nue. The proposed flow performance curve which provides ηeff for an arbitrary Nue shows that ηeff in viscoelastic fluid flow compared to Newtonian fluid flow is small independently of the fluid transport distance, and that the installation of heat transfer enhancement devices has a positive effect on energy-saving in certain ranges of Reynolds numbers and fluid transport distances.

Heat transfer enhancement in turbulent drag reducing surfactant solutions by agitated heat exchangers

Drag reducing solutions can reduce turbulent pressure loss by nearly 90% and can decrease pumping energy requirements and increase flow rates in fluid flow systems. Unfortunately, drag reduced flow is accompanied by lower convective heat transfer coefficients, which is undesirable in district heating and cooling systems, heated tube bundles for undersea petroleum production, and other recirculating heat transport systems.In this study, three different rotating agitators were installed inside the inner tube of a concentric tube heat exchanger to enhance heat transfer in a surfactant drag reducing solution. An earlier mathematical model for heat transfer in scraped surface heat exchangers was adapted for this application so that the effectiveness of agitators with different geometries could be compared quantitatively. In addition, an enhancement efficiency factor was defined to compare power efficiency with previous methods. It was found that agitation can increase the effective inner heat transfer coefficient to exceed that of pure water; heat transfer reduction compared to water was reduced from 60% to −20%. In addition, the enhancement can be more energy-efficient than that of previously studied static mixers.

Intentional mechanical degradation for heat transfer recovery in flow of drag-reducing surfactant solutions

Temporary intentional mechanical degradation of surfactant solutions was investigated as a method of heat transfer recovery for heat exchangers installed in recirculating systems where surfactant solutions are used as drag-reducing additives. Heat transfer recovery is particularly important for implementation of the drag reduction technology in systems such as buildings or district heating and cooling. We studied and quantified the degradation and subsequent recovery processes associated with this heat transfer recovery technique, and the strong effect of fluid temperature on recovery. Some of the important issues for successful implementation of the approach studied here include also the efficiency of the degradation devices and the optimization of the relevant properties of surfactant solutions, which are both needed to achieve maximum overall drag reduction in the system while still maintaining sufficient heat transfer in the exchangers. These results and the concepts related to heat transfer recovery in heat exchangers are discussed in terms of practical implementation considerations and in light of the results from an associated field test conducted in a hydronic cooling system in a building.

EXPERIMENTAL STUDY ON THE COLLABORATIVE DRAG REDUCTION PERFORMANCE OF A SURFACTANT SOLUTION IN GROOVED CHANNELS

Abstract Turbulence with a relatively larger vortex is obtained in drag-reducing surfactant solution, which provides an excellent condition for the application of small scale grooves. In this work, the coupling drag reduction performance of surfactant solution and grooves was experimentally investigated to explore the complementary possibility between their drag reduction mechanisms. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC) mixed with the counterion salt sodium salicylate (NaSal) was experimented in smooth or grooved channel, respectively, at the mass concentrations of 50-150 ppm. It was found that the surfactant solutions gave more effective drag reduction in the grooved channel by the interaction between the restriction effect and peak effect of grooves. Moreover, the critical temperature and critical Reynolds number of the surfactant solution were smaller in the grooved channel, and the friction factor in the grooved channel increased much more rapidly than that in the smooth channel when Re is larger than a critical value.

Analysis of an organized turbulent structure using a pattern recognition technique in a drag-reducing surfactant solution flow

This work presents the investigation for an organized turbulent structure in a drag-reducing flow of dilute surfactant solution by utilizing a particle image velocimetry system to perform the pattern recognition technique on a trajectory in four quadrants of streamwise and wall-normal velocity fluctuations. The pattern recognition is added to a new algorithm in order to directly capture the spatial rotation motion. The Reynolds number based on the channel height and bulk mean velocity was set to 1.5×104. Surfactant solution with a weight concentration of 150ppm was employed and the drag reduction rate was 65%. In the drag-reducing flow, we observe increased frequencies of occurrence of the flow events that correspond to a meandering motion in the wall-normal direction of the high-and low-speed regions. Three findings from investigation of the ensemble-averaged Reynolds shear stress and vortex structure are as follows: (i) the Reynolds shear stress in the large fluctuation range occurs in the narrow region; (ii) Size, strength, arrangement and inclination in the spatial vortex structure in the drag-reducing flow differ from those of the water; and (iii) all trajectory contributions for the wall friction coefficient decrease. Finally, we interpreted that the viscoelasticity characterizing the viscoelastic stress and relaxation time in rheological properties of the flow changes specific elementary vortex for the drag-reducing flow, and the trajectories of each flow pattern change drastically.

Experimental study on drag reduction performance of surfactant flow in longitudinal grooved channels

Drag-reducing surfactant solution can provide a large-eddy environment for longitudinal microgrooves and may realize the complementarity between their drag-reduction mechanisms. In this work, the collaborative drag reduction performance of surfactant solution and longitudinal microgrooves was experimentally studied to verify the speculation about their complementary possibility. The mixture aqueous solution of cationic surfactant (cetyltrimethyl ammonium chloride) and counterion salt (NaSal) was tested in the smooth and two longitudinal microgroove channels respectively at the mass concentrations of 0.16–0.47mmol/L. It was found that the drag reduction performance of surfactant solution was enhanced by the longitudinal microgrooves. The drag-reduction mechanisms of microgrooves in water and surfactant solution were illustrated by the competition between the “peak effect” and the “restriction effect” of microgroove. Moreover, the “second peak effect” was proposed to explain the drag-reduction enhancement mechanisms for surfactant flow in microgroove channels. The groove with a larger size and roughness which might increase the drag in water could still enhance the drag reduction effectiveness of surfactant flow, and had a lower critical temperature and critical Reynolds number in surfactant solution, indicating a promising application in the heat transfer and drag reduction field. Moreover, the results of particle image velocimetry of smooth channel indirectly verified that the drag-reducing mechanism of microgroove was related to the turbulent vortex scale and the restriction effect on near-wall vortices.

Steady Shear and Dynamic Properties of Drag Reducing Surfactant Solutions

Steady Shear and Dynamic Properties of Drag Reducing Surfactant Solutions

J0550302 抵抗低減界面活性剤水溶液の円管流れにおけるミセル構造と乱流遷移の関係

In general, the drag-reducing effect in a pipe by a surfactant additive is attributed to rod-like micelles in the surfactant solution. This paper describes the results of experiments performed for determining the relationship between the micelle structure in the surfactant solution and the drag-reducing effect in a pipe flow. The experimental apparatus is circulation type by using pump and inner diameter of test pipe is 10.6mm. A fluorescence probe method was used to examine the micelle structure in the drag-reducing surfactant solution flow. Pyrene-1-carboxaldehyde was used as the fluorescence probe. The obtained experimental results were as follows. When the drag-reducing surfactant solution was irradiated with ultraviolet light, the fluorescence intensity at the wavelength of 487nm varied with the micelle structure. The fluorescence intensity decreased with the generation of the Shear Induced Structure (SIS) and increased with the disappearance of the SIS. The fluorescence intensity near the pipe wall increased simultaneously with the flow transitions to turbulence. In other words, the turbulent transition occurs along with the disappearance of the SIS near the wall.

M1003 界面活性剤水溶液の抵抗低減流れにおけるミセル構造の崩壊と乱流遷移の関係(GS5 流体工学(3),修士研究発表セッション)

M1003 界面活性剤水溶液の抵抗低減流れにおけるミセル構造の崩壊と乱流遷移の関係(GS5 流体工学(3),修士研究発表セッション)

1208 微小管内流れにおける抵抗低減界面活性剤水溶液の擬層流化現象(GS05-2 熱工学・流体工学)

1208 微小管内流れにおける抵抗低減界面活性剤水溶液の擬層流化現象(GS05-2 熱工学・流体工学)

Effect of Air Injection on Drag-Reducing Surfactant Solution in an Upward Vertical Pipe Flow

Effect of Air Injection on Drag-Reducing Surfactant Solution in an Upward Vertical Pipe Flow

Heat Transfer Enhancement for Drag-Reducing Surfactant Fluid Using Photo-Rheological Counterion

A new heat transfer enhancement method for a drag-reducing surfactant solution using a photo-rheological counterion was discussed. Surfactant and counterion concentration effect on heat transfer enhancement was investigated combining with rheological test. Surfactant/counterion concentration of 4 mM/5 mM was considered as an efficient concentration for heat transfer enhancement.

Relaxation Behavior of a Drag-Reducing Cationic Surfactant Solution

Relaxation Behavior of a Drag-Reducing Cationic Surfactant Solution

Effective Wall Slip in Couette and Parallel Plates Flow of Drag-Reducing Surfactant Solutions

Abstract This paper presents experimental results of the study on the rheological properties of drag-reducing surfactant solutions. It is the main objective of the present work to establish the possibility of wall slip corrections for Couette and parallel plates rheometers. In addition, methodology of samples preparation of aqueous surfactant solutions to rheological measurements is presented. In the study the cationic surfactant cethyltrimethylammonium chloride (CTAC) was used. The additive enhancing micellar association was sodium salicylate (NaSal). In solutions used the molar ratio of CTAC to NaSal was in the range from 1 to 2. Concentrations of the solutions were equal to 1000 and 6000 ppm. Experimental data presented show that during the flow curve measurements for surfactant solutions there is a possibility of occurrence an effective wall slip. Correcting measurement results by the use of simple methods does not provide guaranties to obtain real flow curve characteristics. Best solution seems to be in using the measuring systems with rough surfaces.

J054044 マイクロバブルを含む垂直上昇気液二相流の流動伝熱特性

The heat-transfer coefficients decrease in a drag-reducing surfactant solution flow. Therefore, it is necessary to develop an effective method for enhancing the heat transfer of a surfactant solution flow. The objective of this study is to examine the heat transfer enhancement effect when microbubbles are injected into a drag-reducing surfactant solution flow. Specifically, the relationship between microbubble size and the heat transfer enhancement of a surfactant solution flow was investigated experimentally. Microbubbles were generated using a porous metal pipe placed in a test pipe. The flow patterns observed in air microbubble-surfactant solution two-phase flows were fine bubbly; these patterns were independent of microbubble size. The heat transfer enhancement effect depends on the air-surfactant solution flow ratio or microbubble size. An increase in the air-surfactant solution flow ratio or decrease in the microbubble size leads to a greater heat transfer enhancement effect.

Heat transfer in the thermal entrance region for drag reduction surfactant solutions in pipe flow

Experimental results relating to heat transfer for a flow of surfactant solutions in the thermal entrance region of a pipe were discussed. Aqueous solutions of hexadecyltrimethylammonium chloride with addition of sodium salicylate were used as model fluids. It was observed that the effect of buoyancy on the heat transfer process was less pronounced in the entrance region of a pipe than in the scope of a fully developed flow. It was demonstrated that it was possible to correlate experimental results for the flow of drag-reducing surfactant solutions, based on the dependence of Nusselt number on a dimensionless longitudinal coordinate. In addition, simple empirical equations were proposed which enable the local and mean values of the heat transfer coefficient to be calculated.