Drag-reducing Surfactant Solution Research Articles

211 抵抗低減用界面活性剤水溶液の単一円柱周りの流動特性に関する研究

211 抵抗低減用界面活性剤水溶液の単一円柱周りの流動特性に関する研究

Heat Transfer Enhancement of Drag-Reducing Surfactant Solution Flow in a Circular Tube.

Heat Transfer Enhancement of Drag-Reducing Surfactant Solution Flow in a Circular Tube.

Asymptotes of maximum friction and heat transfer reductions for drag-reducing surfactant solutions

A new maximum drag reduction asymptote (MDRA) for surfactant solutions is presented. Various concentrations including cationic and non-ionic surfactant solutions were used to experimentally determine this asymptote. It is shown that if solvent viscosity is used to compute Reynolds and Prandtl numbers for viscous solutions, it leads to underestimations of the friction coefficient. To avoid uncertainties in the selection of the fluids viscosity, most solutions used were intentionally conditioned so their shear viscosity was water-like in the ranges covered. Using the same solutions, a maximum heat transfer reduction asymptote (MHTRA) was also determined – a correlation that did not exist for surfactants until now. Finally, by using slightly modified definitions to quantify the heat transfer and drag reductions (TRH and TRD), it is possible to express the ratio between the MHTRA and MDRA with a constant value of 1.06, independent of Reynolds number. This relationship can be used as an auxiliary criterion to determine whether or not a solution is asymptotic when there is an uncertainty about the shear viscosity.

Enhanced heat transfer of drag reducing surfactant solutions with fluted tube-in-tube heat exchanger

Solutions containing drag reducing additives also show reduced heat transfer which limits their use in hydronic cooling and heating systems where heat exchange is critical. For Reynolds numbers 10,000–50,000 and test fluid inlet temperatures 50–70°C, a fluted inner tube heat exchanger showed increased heat transfer coefficients for both cationic and zwitterionic/anionic drag reducing surfactant solutions. The pressure drop penalty for heat transfer enhancement of the cationic surfactant solution flowing through the fluted tube is high while for the zwitterionic/anionic solution, significant heat transfer improvement was achieved with only a modest pressure drop penalty.

Drag Reduction and Its Application. Transition in Pipe Flow of Drag-Reducing Surfactant Solution.

Transition in pipe flow of drag reducing surfactant solution (C14TABr) has been studied experimentally. Two stainless pipes with inside diameter of 3.03 mm and 2.04 mm are used and the measurements of pressure drop and pressure fluctuations are carried out. In the case of surfactant solution, turbulence appears at higher Reynolds number than that for water and the flow is stabilized. In contrast to the flow of polymer solution, critical Reynolds number for surfactant solution doesn't decrease even in the case of smooth inlet condition, except for the case of high concentration solution. With an increase in the concentration of solution, critical Reynolds number becomes to be unaffected by the pipe inlet conditions. When the surfactant solution is used, frequency of pressure fluctuation becomes higher and amplitude of it becomes less than that for water.

Drag Reduction and Its Application. Flow of Drag-Reducing Surfactant Solutions Through a Sudden Expansion Pipe.

Flow of surfactant solution (C14 TABr and ARQUAD) through a sudden expansion pipe is studied experimentally from measurements of pressure distribution, velocity profile, and flow visualization. Two acrylic pipes with inside diameters of 15 mm and 30 mm are joined and the test section with 5.4 m length is used. Velocity profiles are measured by LDV. In the case of surfactant solution, loss coefficient of sudden expansion is lower than that for water at low Reynolds number. Pressure recovery length and reattachment length for surfactant solution increase remarkably compared with the case of water. In the sudden expanded pipe, fluid near the center of the pipe is very fast, while reverse flow appears near the wall. This flow becomes more remarkable for surfactant solution than for water.

A105 界面活性剤水溶液の噴流特性におよぼす温度の影響(オーガナイズドセッション1 : 機能性流体の熱伝達)

The present experiment study is conducted to examine the near field characteristics of the axisymmetric jet discharged from circular pipe for a dilute drag-reducing surfactant solution (Ethoquad O/12). The temperature effect on the jet behavior is studied for a fixed Reynolds number of 10000. It is found that the turbulence suppression effect reduces with the development of jet and strongly depends on the temperature.

1002 界面活性剤水溶液の抵抗減少流れにおける乱れ構造の可視化

Turbulent structure in the two-dimensional channel flow of drag-reducing surfactant solution is investigated using hydrogenbubble technique. The visual observations are focussed on the coherent motions in the near-wall region; i.e., ejections and quasi-streamwise vortices. It is revealed that the ejections of near-wall fluid are suppressed in the drag-reducing flows. The ejection could not be observed when ‘turbulence reduction – drag’ (TRD) is larger than 75%, where TRD is defined using the friction difference between laminar and turbulent flows (Gasljevic and Matthys [2]). It is found that quasi-streamwise vortices exist even at large TRD above 80%. The average position of the quasi-streamwise vortex centre becomes more distant from the wall as TRD increases. Introduction It is well known that some kinds of surfactant solution cause a remarkable drag reduction in turbulent flows. Many investigations have been conducted concerning this problem [3,12]. The measurements using LDV (laser Doppler velocimetry) show that the Reynolds shear stress is close to zero in surfactant solutions with large drag reduction [3,11]. Warholic et al. [11] conjectured that the quasi-streamwise vortices do not exist near the wall under maximum drag reduction. In our previous experiment [5], we visualized lowspeed streaks in the two-dimensional channel flow of dragreducing surfactant solutions and showed that the low-speed streaks exist even at large drag reduction. It was also revealed that, in the drag-reducing flows, the mean streak spacing reaches a minimum at some distance from the wall and the streaks decrease rapidly with approaching the wall. In order to interpret these experimental evidences, the coherent motions near the wall (ejections and quasi-streamwise vortex motions) are visualized in the present work. Hydrogen-bubble technique is widely used to visualize the coherent motions. Experimental Apparatus and Procedure The experimental apparatus used in this work is the same with the one used before [4]. The two-dimensional channel is made of acrylic plates and the dimensions are the width W = 40 mm, the height H = 400 mm and the length L = 4 m. The pressure drops were measured from static pressure taps situated at 65W~90W downstream from the channel inlet. The velocity measurements and the visual observations of near-wall turbulent structures were made using the hydrogen-bubble technique [6,9]. Figure 1 shows the details of the measuring section. The wire used for generating hydrogen-bubbles was a 30μm stainless-steel wire. A DC pulse generator was used to generate hydrogen-bubbles, and the hydrogen-bubble time-lines or sheets were viewed and recorded using a CCD video camera and a VTR. The individual video frames were converted to a digital array using an imageprocessing system and then analysed by a microcomputer. Th mixt salic impu filter were Exp Pres Fi versu figur

Coupling Between Heat and Momentum Transfer Mechanisms for Drag-Reducing Polymer and Surfactant Solutions

Drag-reducing solutions exhibit simultaneous friction and heat transfer reductions, yet it has been widely believed that there is no direct coupling between the two. In this work, we have conducted a study to re-examine this issue, using measurements of friction and heat transfer over a wide range of flow conditions from onset to asymptotic, various pipe diameters, and several polymer and surfactant solutions. Contrary to some earlier suggestions, our tests show that no decoupling of the momentum and heat transfer mechanisms was seen at the onset of drag reduction, nor upon departure from the asymptotes, but rather that the friction and heat transfer reductions change simultaneously in those regions. For asymptotic surfactant and polymer solutions, the ratio of heat transfer and drag reductions was seen to be constant over a large range of Reynolds numbers, if modified definitions of the reduction parameters are used. In the nonasymptotic region, however, the ratio of heat transfer to drag reductions is higher and is a function of the reduction level, but is approximately the same for polymer and surfactant solutions. This variation is consistent with the concept of a direct coupling through a nonunity constant Prt, as also suggested by our local measurements of temperature and velocity profiles. We also saw that our diameter scaling technique for friction applies equally well to heat transfer. These findings allow us to predict directly the heat transfer from friction measurements or vice versa for these drag-reducing fluids, and also suggest that a strong coupling exists between the heat and momentum transfer mechanisms.

C602 界面活性剤水溶液噴流の速度分布

The present study describes the velocity profiles in a circular pipe jet of drag-reducing surfactant solution. The Reynolds number covers from 5000 to 20000, and the velocity field is measured by LDV. It is revealed that the radial momentum transport is significantly reduced at Re 5000, but the reduction becomes insignificant at higher Reynolds numbers.

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 ...

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.

Experimental Investigation of Thermal and Hydrodynamic Development Regions for Drag-Reducing Surfactant Solutions

The reductions in friction and heat transfer exhibited by a surfactant solution in the entry region of a circular pipe were measured and analyzed, with special attention paid to the relationship between the local heat transfer and friction. Two entrance configurations were used, a cone contraction and wire mesh plugs used as a device for velocity profile flattening. Both the simultaneous development of temperature and velocity profiles and the development of temperature profile with hydrodynamically predeveloped flow were studied. Interestingly, the local heat transfer measurements for surfactant solutions matched very well a correlation developed for polymer solutions, but for surfactants the development of the heat transfer and velocity profiles appear coupled, unlike what is thought to happen for polymer solutions. The development patterns appear to be independent of velocity and entrance type at low disturbance levels. At high disturbance levels, however, some striking changes in the fluid itself, likely due to temporary micellar structure degradation by high local shear stress in the inlet region, were observed as well, and quantified.

界面活性剤水溶液の抵抗減少流れにおけるストリーク構造

The characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method. The mean velocity profiles and the distributions of streamwise turbulence intensity are also obtained. It is shown that, at a large drag reduction rate DR, the profile of the streamwise turbulence intensity has a plateau region around its peak. In the drag-reducing flow, the mean spanwise streak spacing reaches minimum at some distance from the wall. In the drag-reducing flow of high-density(1000 ppm)surfactant solution, the low-speed streaks appear intermittently at the Reynolds number smaller than those for the 'hump' of the f-Re curve(f:friction factor). The mean spanwise streak spacing very near the wall increases as DR becomes large. It is speculated that the nondimensional wall-normal distance y+ of the center of streamwise vortices is larger for the flow of large DR compared with that for the Newtonian fluid flow.

Rheological and rheo-optical characterization of shear-induced structure formation in a nonionic drag-reducing surfactant solution

We know of only a few rheological studies of nonionic surfactant solutions, and these did not show clear evidence of shear-induced structures (SIS) formation. This paper reports, however, some rheological and rheo-optical results for nonionic surfactant solutions at different concentrations and temperatures that do show clear evidence of such SIS formation. For example, in a 0.3% SPE 95285 solution at 5 °C, the shear viscosity, N1, and flow birefringence start from a low level and takes tens of seconds to grow to a high plateau region upon the application of a 100 s−1 shear. The re-application of the same shear after rest following a preshear indicates that the effect of the shear persists for a very long time (hundreds of seconds). These transient flow results resemble those exhibited by cationic surfactants or associating polymer solutions. The time needed for the viscosity and N1, to reach plateau values generally decrease with increasing shear rate and temperature. At moderate shear rates, the N1 and ...

Characteristics of Low-Speed Streaks in the Flow of Drag-Reducing Surfactant Solution.

The characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method. The mean velocity profiles and the distributions of streamwise turbulence intensity are also obtained. It is shown that, at a large drag reduction rate DR, the profile of the streamwise turbulence intensity has a plateau region around its peak. In the drag-reducing flow, the mean spanwise streak spacing reaches minimum at some distance from the wall. In the drag-reducing flow of high-density(1000 ppm)surfactant solution, the low-speed streaks appear intermittently at the Reynolds number smaller than those for the 'hump' of the f-Re curve(f:friction factor). The mean spanwise streak spacing very near the wall increases as DR becomes large. It is speculated that the nondimensional wall-normal distance y+ of the center of streamwise vortices is larger for the flow of large DR compared with that for the Newtonian fluid flow.

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.

Turbulent Characteristics of Drag-Reducing Flow of Surfactant Solutoin.

Turbulent characteristics of a drag-reducing surfactant solution in a two-dimensional channel flow are measured by means of a hot-film anemometer. It is confirmed for the drag-reducing flow that the mean velocity profiles on the semilogarithmic plot are S-shaped at high drag reduction and the ratio of the wall-normal turbulence intensity υ'rms to the streamwise u'rms is constant within a region near the wall. At a distance from the wall, the large-amplitude turbulent velocity fluctuations are more intermittent than in the corresponding water flow. The generation of Reynolds shear stress is maximized in a very-low-frequency range of turbulent fluctuations. The energy content of the turbulent fluctuations decreases at the intermediate frequency range.

Characterization of micellar structure dynamics for a drag-reducing surfactant solution under shear: normal stress studies and flow geometry effects

Some surfactant solutions have been observed to exhibit a strong drag reduction behavior in turbulent flow. This effect is generally believed to result from the formation of large cylindrical micelles or micellar structures. To characterize and understand better these fluids, we have studied the transient rheological properties of an efficient drag-reducing aqueous solution: tris (2-hydroxyethyl) tallowalkyl ammonium acetate (TTAA) with added sodium salicylate (NaSal) as counter ion. For a 5/5 mM equimolar TTAA/NaSal solution, there is no measurable first normal stress difference (N1) immediately after the inception of shear, but N1 begins to increase after a well-defined induction time — presumably as shear-induced structures (SIS) are formed — and it finally reaches a fluctuating plateau region where its average value is two orders of magnitude larger than that of the shear stress. The SIS buildup times obtained by first normal stress measurements were approximately inversely proportional to the shear rate, which is consistent with a kinetic process during which individual micelles are incorporated through shear into large micellar structures. The SIS buildup after a strong preshear and the relaxation processes after flow cessation were also studied and quantified with first normal stress difference measurements. The SIS buildup times and final state were also found to be highly dependent on flow geometry. With an increase in gap between parallel plates, for example, the SIS buildup times decreased, whereas the plateau viscosity increased.

Rheological behavior and birefringence investigations on drag-reducing surfactant solutions of tallow-(tris-hydroxyethyl)-ammonium acetate/sodiumsalicylate mixtures

Rheological and flow birefringent properties of a drag-reducing mixture of tallow-(tris-hydroxiethyl)-ammonium acetate (ETHOQUAD T/13-50) and sodiumsalicylate (NaSal) have been studied as a function of the concentration and of the salt/surfactant molar ratio x. The optimum molar ratio x for drag reduction is around 2.5. It is shown that shear-induced supramicellar structures (SIS) which are believed to be responsible for friction reduction in turbulent pipe flow develop in the presence of NaSal. It was observed that SIS are also formed even if the concentration c exceeds c*, i.e., the concentration where the volumes of rotation of the individual rodlike micelles start to overlap. The validity of the stress optical law is discussed. A switch from a reptation-controlled stress relaxation to a kinetically controlled mechanism takes place at x ≈ 2.5 for this system.