Drag-reducing Surfactant Solution Flow Research Articles

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.

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.

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.

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)

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.

305 抵抗低減界面活性剤水溶液流れの流動伝熱特性に及ぼす微細気泡混入の影響(OS-2 熱流体力学における非線形現象の解析・制御(2))

305 抵抗低減界面活性剤水溶液流れの流動伝熱特性に及ぼす微細気泡混入の影響(OS-2 熱流体力学における非線形現象の解析・制御(2))

Flow of drag-reducing surfactant solutions in rough pipes

The paper reports the results of experimental study of the flow of hexadecyltrimethylammonium chloride (CTAC) solutions with addition of sodium salicylate (NaSal) in the rough pipes. Measurements were performed in the range of the surfactant concentration from 200 to 400 ppm at a constant molar ratio CTAC/NaSal of 1:2. Five pipes of the relative roughness k/ D varying from 1.2 × 10 −2 to 5.6 × 10 −2, obtained by the covering of inner surface of the pipes with glued silicon carbide particles of different size, were studied. The roughness was observed to increase the drag of flow of CTAC/NaSal solutions already at Reynolds numbers higher than 800. With increasing relative roughness k/ D, the critical value of Reynolds number, at which the drag reduction disappears, was found to decrease. However, no influence of the roughness on the critical shear stress was noted. The ratio of the critical Reynolds number for rough pipes to that of hydraulically smooth pipes was independent of the surfactant concentration. The degree of drag reduction by the flow of surfactants was greater in rough pipes than in smooth pipes.

459 微細気泡混入による界面活性剤水溶液の伝熱促進(GS 流体工学3)

459 微細気泡混入による界面活性剤水溶液の伝熱促進(GS 流体工学3)

Friction and heat transfer in drag-reducing surfactant solution flow through curved pipes and elbows

A study of drag-reducing flow in curved pipes was conducted. In contrast to earlier studies we show that if we use a modified definition of drag reduction that includes only the turbulence effects, we observe indeed the same level of drag reduction in both coiled and straight pipes. More complex results showing reduced drag reduction compared to curved pipes were achieved with elbows. Two elbows of different size and type were tested in turbulent flow of both water and drag-reducing surfactant solution. A more elaborate analysis was conducted for a half-inch threaded elbow with a ratio of curvature radius to diameter of 1.2. The pressure drop and heat transfer were measured in a section downstream from the elbow over a distance of x/ D = 130 in order to investigate the hydrodynamic and thermal developments of the flow. The pressure drop coefficient of the elbow was calculated for water and a surfactant solution, based on the total increase in pressure drop in the system due to the presence of the elbow. For a larger welded elbow of 6″ diameter some drag reduction was measured for the surfactant solution.

Experimental study on the effects of shear induced structure in a drag-reducing surfactant solution flow

In this paper, The drag reduction characteristics of surfactant solutions have been experimentally studied, as well as, the shear viscosities of turbulent drag-reducing surfactant solution have been measured as a function of concentration, shear rate and temperature by using AG-G2 (TA Instruments, New Castle, USA) rheometer. In comparison the rheological property with the macroscopic behavior of the solutions in turbulent channel flow, a deeper insight into the mechanisms of drag-reducing surfactant solution has been obtained. For no shear induced structure of surfactant solutions they just show features shear thinning, but the drag reduction is very significant phenomenon. Surfactant solution of the shear induced structure is not a surfactant fluid drag reduction of the necessary elements.

Reynolds-number dependence of turbulence structures in a drag-reducing surfactant solution channel flow investigated by particle image velocimetry

The Reynolds-number dependence of turbulence structures in a drag-reducing surfactant solution flow is attributed to the Reynolds-number effect on rheology of the solution flowing in the passage and the rheological properties are associated with the shear-induced structure (SIS) formed in a sheared surfactant solution. Through analysis of turbulence statistics of the two-dimensional velocity field, measured by particle image velocimetry, for a drag-reducing flow with addition of cetyltrimethyl ammonium chloride (CTAC) in different flow regimes characterized by the drag-reducing effectiveness dependent on the Reynolds number, we studied the characteristics of turbulence structures for different Reynolds-number-dependent flow states and indirectly revealed the dynamic processes of SIS across the flow passage. A 25ppm (ppm—parts per million) CTAC solution at 30°C was tested. Based on the relationship between the Reynolds number and the drag-reduction levels, the CTAC solution flow was categorized into four regimes: Regime I is laminar and transitional flow without drag-reducing ability; in regime II drag-reduction level increased with the Reynolds number; in regime III drag-reduction level decreased with the Reynolds number; and in regime IV drag-reducing ability disappeared. Five cases of CTAC solution flow—two in regime II, two in regime III, and one in regime IV—were measured. Five cases of water flow at similar Reynolds numbers corresponding to those of CTAC solution flows were also measured for comparison. It was found that the flows in regimes II and III behave differently in turbulence statistics, including mean streamwise velocity, turbulence intensities of both streamwise and wall-normal velocity components, Reynolds shear stress and contour map of spectral density functions of velocity fluctuations in a coordinate plane of wave number and wall-normal position, regardless of similar drag-reduction levels. In regimes III and IV, multilayer structures associated with different flow states were obtained from the analysis of profiles of the Reynolds shear stress and the viscoelastic shear stress, which characterize the dynamic processes of SIS in the solution across the flow passage at different Reynolds numbers.

Development characteristics of fluctuating velocity field of drag-reducing surfactant solution flow in a duct

Development behavior of the fluctuating velocity of surfactant solution in a duct has been studied experimentally. The concentration of surfactants was kept constant at 1,000 ppm, mean velocity at 0.78 m/s and fluid temperature at 15 °C. Using laser Doppler velocimetry, the fluctuating streamwise velocity distributions at six cross sections, which ranged from 14 to 112 times of hydraulic diameter of the duct, were measured. From the results, the fluctuating structures of surfactant solution flow are observed to have structures different from that of turbulent water flow in the developing field. The wavelet analysis reveals that the high-level fluctuation of surfactant solution flow is characterized by periodicity rather than irregularity around the position where the fluctuation intensity takes a peak value and that the period and the scale of periodic flow structures are related to the relaxation times of the fluid. This indicates that the high-level fluctuation is deeply related to the elastic instability and has a different generation mechanism from that of turbulence observed in a Newtonian turbulent flow.

Investigation on the characteristics of turbulence transport for momentum and heat in a drag-reducing surfactant solution flow

Simultaneous measurements of the velocity (u and ν in the streamwise and wall-normal directions, respectively) and temperature fluctuations (θ) in the thermal boundary layer were carried out for a heated drag-reducing surfactant solution flow in a two-dimensional channel by means of a two-component laser Doppler velocimetry and a fine-wire thermocouple probe. The drag-reducing fluid tested was a dilute aqueous solution of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), with 30 ppm concentration. Measurements were performed for CTAC solution flows at an inlet temperature of 31 °C and at three Reynolds numbers of 3.5×104, 2.5×104, and 1.5×104, respectively, and for water flow at the Reynolds number of 2.5×104. Drag reduction (DR) and heat transfer reduction (HTR) for the three CTAC solution flows were DR(HTR)=33.0(20.2), 70.0(77.3), and 65.1(77.0) percentage, respectively. At a high HTR level, a large temperature gradient appeared when y+<50 in the measured range (the superscript “+” denotes normalization with inner variables). Temperature fluctuation intensity, θ′+, and the streamwise turbulent heat flux, u+θ+¯, were enhanced in the layer with large temperature gradient for the drag-reducing flow, whereas the wall-normal turbulent heat flux, −ν+θ+¯, was depressed throughout the measured range. The depression of −ν+θ+¯ was due to a cause similar to that of the depression of the Reynolds shear stress −u+ν+¯, i.e., in addition to the decrease of ν′+, decorrelation between the two variables occurred. The decrease of −ν+θ+¯ resulted in HTR, which was similar to that of the decrease of −u+ν+¯ resulted in DR for the drag-reducing flow by additives. The turbulence production terms, −u+ν+¯(∂U+/∂y+) and −ν+θ+¯(∂Θ+/∂y+) where U and Θ are mean velocity and temperature, were reduced in the drag-reducing CTAC solution flows. The estimated power spectra of temperature fluctuations implied that the drag-reducing surfactant additive depressed the turbulence at high frequencies or at small scales, whereas it increased the turbulent energy at low frequencies or at large scales. The profiles of the eddy diffusivities for momentum and heat in the CTAC solution flows were both decreased. The turbulent Prandtl number deviated from that of the water flow near the heated wall with a value close to the molecular Prandtl number of the solvent.

Development characteristics of drag-reducing surfactant solution flow in a duct

Development characteristics of dilute cationic surfactant solution flow have been studied through the measurements of the time characteristics of surfactant solution by birefringence experiments and of the streamwise mean velocity profiles of surfactant solution duct flow by a laser Doppler velocimetry system. For both experiments, the concentration of cationic surfactant (oleylbishydroxymethylethylammonium chloride: Ethoquad O/12) was kept constant at 1000 ppm and the molar ratio of the counter ion of sodium salicylate to the surfactants was at 1.5. From the birefringence experiments, dilute surfactant solution shows very long retardation time corresponding to micellar shear induced structure formation. This causes very slow flow development of surfactant solution in a duct. Even at the end of the test section with the distance of 112 times of hydraulic diameter form the inlet, the flow is not fully developed but still has the developing boundary layer characteristics on the duct wall. From the time characteristics and the boundary layer development, it is concluded that the entry length of 1000 to 2000 times hydraulic diameter is required for fully developed surfactant solution flow.

Simultaneous measurements of velocity and temperature fluctuations in thermal boundary layer in a drag-reducing surfactant solution flow

The mechanism of turbulent heat transfer in the thermal boundary layer developing in the channel flow of a drag-reducing surfactant solution was studied experimentally. A two-component laser Doppler velocimetry and a fine-wire thermocouple probe were used to measure the velocity and temperature fluctuations simultaneously. Two layers of thermal field were found: a high heat resistance layer with a high temperature gradient, and a layer with a small or even zero temperature gradient. The peak value of \( \overline{{u^{ + } \theta ^{ + } }} \) was larger for the flow with the drag-reducing additives than for the Newtonian flow, and the peak location was away from the wall. The profile of \( - \overline{{v^{ + } \theta ^{ + } }} \) was depressed in a similar manner to the depression of the profile of \( - \overline{{u^{ + } v^{ + } }} \) in the flow of the surfactant solution, i.e., decorrelation between v and θ compared with decorrelation between u and v. The depression of the Reynolds shear stress resulted in drag reduction; similarly, it was conjectured that the heat transfer reduction is due to the decrease in the turbulent heat flux in the wall-normal direction for a flow with drag-reducing surfactant additives.

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.

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.

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