DNS study by a bilayer model on the mechanism of heat transfer reduction in drag-reduced flow induced by surfactant

A bilayer model proposed in [1] is used to investigate the mechanism of heat transfer reduction of surfactant-induced drag-reducing channel flow with a constant heat flux imposed on both walls by direct numerical simulation. In the bilayer model, Newtonian fluid and viscoelastic fluid are assumed to coexist with shear stress balance satisfied between the two fluid layers. A Giesekus model is used to model the viscoelastic fluid induced by the addition of surfactant additives. High-order compact difference schemes are applied to discretize the convective and diffusion terms whereas MINMOD scheme is used to discretize the convective terms in the Giesekus constitutive equations to enhance numerical stability. The effectiveness of the surfactant additives at different flow region on heat transfer reduction is investigated.     

Effect of Non-Newtonian Viscosity for Surfactant Solutions on Vortex Characteristics in a Swirling Pipe Flow

Effects of non-Newtonian viscosity for surfactant solution on the vortex characteristics and drag-reducing rate in a swirling pipe flow are investigated by pressure drop measurements, velocity profile measurements and viscosity measurements. Non-Newtonian viscosity is represented by power-law model (T = kD n). Surfactant solution used has shear-thinning viscosity with n < 1.0. The swirling flow in this study has decay of swirl and vortex-type change from Rankin's combined vortex to forced vortex. It is shown that the effect of shear-thinning viscosity on the decay of swirl intensity is different by vortex category and the critical swirl number with the vortex-type change depends on shear-thinning viscosity.     

添加筛网增强减阻流体湍流特性的试验研究

应用粒子图象测速仪对添加筛网后的CTAC(Cetyltrimethyl Ammonium Chloride)减阻流体湍流流场进行试验研究,得到了在筛网后不同位置的减阻流体湍流速度分布和平均速度分布。研究表明：在靠近筛网处,减阻流体的平均速度分布趋向于和水的速度平均分布相一致,而在远离筛网处,其平均速度分布趋向于减阻流体不加筛网时的平均速度分布;在筛网附近,CTAC减阻流体湍流核心区明显增大,在近壁面处出现强烈的漩涡波动,瞬间速度空间分布趋近于水的速度空间分布,在远离筛网处,CYAC减阻流体过度层明显增厚,在湍流核心区和过度层之间出现小漩涡,这表明被金属筛网破坏的胶束重新缔合成棒状胶束,恢复了减阻性能。     

Structural analysis of turbulent transport in a heated drag-reducing channel flow with surfactant additives

Turbulence transport features in a heated drag-reducing surfactant solution (CTAC, 30 wppm) channel flow was investigated by simultaneously measuring velocity and temperature fluctuations in the thermal boundary layer. Measurement was made at inlet fluid temperature of 304 K and at three Reynolds numbers (based on channel height, bulk velocity and solvent viscosity): 3.5 × 10⁴, 2.5 × 10⁴ and 1.5 × 10⁴. Structural analysis showed that the drag-reducing additives inhibited the motions associated with ejections of low-momentum fluid away from the wall and sweeps of high-momentum fluid toward the wall (the second and fourth quadrant motion respectively) but had no obvious effect on the outward motion of high-momentum fluid and wall-ward motion of low-momentum fluid (the first and third quadrant motion respectively). The depression of wall-normal turbulent heat flux was due to the decreased contributions of the second and fourth quadrant motions.     

Experimental Study for Pressure Drop of Viscoelastic Fluids through Periodically Sudden Converging－Diverging Tube

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表面活性剂减阻溶液湍流传热结构研究进展

与聚合物添加剂相比,表面活性剂减阻剂具有寿命长不发生降解的特点,已被广泛地应用到集中供暖(冷)系统。表面活性剂在降低流体湍流摩擦阻力时,溶液的传热性能恶化。为了扩大表面活性剂在传热领域的应用,理解传热下降的原因,针对表面活性剂溶液的湍流传热结构目前开展了一些实验研究和理论分析,但仅处于探索阶段、尚未定论。为了进一步开展研究,对目前国内外关于湍流传热结构的研究,以及取得的成果做了分析和总结,并分析了目前研究存在的问题,对今后继续开展研究提出了自己的观点。     

Forced convective flow and heat transfer characteristics of aqueous drag-reducing fluid with carbon nanotubes added

A new kind of aqueous drag-reducing fluid with carbon nanotubes (CNTs) was developed. The new working fluid was an aqueous CTAC (cetyltrimethyl ammonium chloride) solution with CNTs added and has both special effects of drag-reducing and heat transfer enhancement. The thermophysical and rheological properties of the new working fluid were measured. An experiment was carried out to investigate the forced convective flow and heat transfer characteristics of conventional drag-reducing fluid (aqueous CTAC solution) and the new drag-reducing nanofluid in a test tube having an inner diameter of 25.6 mm. Results indicated that there were no obvious differences of the drag-reducing characteristics between conventional drag-reducing fluid and new drag-reducing nanofluid. However, there were obvious differences of the heat transfer characteristics between both fluids. The heat transfer characteristics of new drag-reducing nanofluid have strong dependences on the liquid temperature, the nanoparticle concentration and the CTAC concentration. The heat transfer enhancement technology of nanofluid could be used to solve the problem of heat transfer deterioration for conventional drag-reducing fluids.     

Viscoelastic effects on the oscillatory flow in a fluid-saturated porous layer

The oscillating flow of the viscoelastic fluid-saturated porous layer has been useful in many areas, including the petroleum, chemical, and bioengineering industries. It is studied using the modified Darcy-Oldroyd-B model in this article. The exact solution is obtained utilizing a simpler and more reasonable method. According to this velocity solution, the time-velocity profile of one kind of viscoelastic fluid is analyzed. From the analysis, it was found that the flow behaves like the Newton fluid when the oscillating frequency is low, and the flow reversal occurs when the oscillating frequency is high. Further, velocity, temperature, shear stress, and the rate of heat transfer are exponential solutions that are obtained and analyzed for different values of known physical parameters. Finally, we recognize that the relaxation and retardation parameters in this model act in the opposite manner.     

DNS of fully developed turbulent heat transfer of a viscoelastic drag-reducing flow

A direct numerical simulation (DNS) of turbulent heat transfer in a channel flow with a Giesekus model was carried out to investigate turbulent heat transfer mechanism of a viscoelastic drag-reducing flow by additives. The configuration was a fully-developed turbulent channel flow with uniform heat flux imposed on both the walls. The temperature was considered as a passive scalar with the effect of buoyancy force neglected. The Reynolds number based on the friction velocity and half the channel height was 150. Statistical quantities such as root-mean-square temperature fluctuations, turbulent heat fluxes and turbulent Prandtl number were obtained and compared with those of a Newtonian fluid flow. Budget terms of the temperature variance and turbulent heat fluxes were also presented.     

一种两性表面活性剂腐蚀性和减阻特性实验研究

首先对两性表面活性剂十八烷基二甲基氧化胺（C20H43NO）的腐蚀性进行了定性测试,结果表明C20H43NO对集中供暖系统管道的腐蚀性较弱（相对于当地自来水）。同时还对C20H43NO水溶液在循环系统中的湍流减阻特性进行了实验研究：主要分析了该种减阻溶液的最佳浓度、温度效应及抗剪切特性等。结果表明：C20H43NO水溶液表现出良好的湍流减阻效应（测得的最大减阻率达到77％）和抗剪切特性,且减阻特性与溶液浓度和温度均有很大的关系;在60℃时减阻最佳浓度约为900ppm;1500ppm和900ppm时有显著减阻效果的温度范围为40～70℃,在低温和高温时不具有明显的减阻现象。     

Experimental investigation of turbulent boundary layer flow with surfactant additives using PIV and PDA

Drag reduction of turbulent water flow with surfactant (CTAC) additives was experimentally investigated. By using PIV and PDA measurements, the spatial velocity distribution of surfactant solution flow was clarified in a two‐dimensional water channel. With an increasing Reynolds number, it was found that drag reduction of surfactant solution flow is enhanced within the region of drag reduction. However, in the region of post drag reduction, the drag‐reducing coefficient approaches one without surfactant when Reynolds number is increased. In the near‐wall region, velocity profiles of the drag‐reducing fluid are similar to, but not the same as, the laminar profiles of the Newtonian fluid. When compared to the case of water flow without surfactant, the velocity contour lines of the drag‐reducing fluid run approximately parallel to the wall. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(2): 99–107, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20047     

Experimental Study of Passive Heat Transfer Enhancement in a Drag-Reducing Flow

Drag and heat transfer reduction were examined in a fully developed two-dimensional drag-reducing flow with different concentrations of surfactant additives. A row of low-profile mixers was used to enhance heat transfer in the flow. The effect of the low-profile mixers on heat transfer enhancement was examined in terms of the local Nusselt number for the surfactant concentration of 90 ppm. A comparison of the cases with and without low-profile mixers show that the average Nusselt number is enhanced by about 170% for Reynolds numbers of 7000, 12000, and 16200 with only a small pressure drop penalty. This increase in heat transfer performance might be related to the longitudinal vortices generated by the low-profile mixers, resulting in the enhancement of the bulk exchange of fluid between the main flow and the near-wall region. It was found that the enhancement of the low-profile mixers to the heat transfer rate starts to deteriorate in the streamwise direction at a certain location downstream of the mixers. The location of the onset of the deterioration shifts downstream with an increase in the Reynolds number.     

Effects of non-isothermal heating on drag reduction in surfactant aqueous solution flow

In this study we investigate the control of flow characteristics and heat transfer of a drag-reducing dilute cationic surfactant solution in a channel, in order to develop a highly efficient heat exchanger. As has been reported by many authors, addition of certain polymers or surfactants reduces heat transfer in drag-reduced water flow. Therefore, other measures must be taken in order to compensate the reduction in heat transfer. Specifically, this study investigates the effects of non-isothermal heating on drag-reduced flow: experiments were conducted in order to study passive control for effecting the drag-reduction state by employing temperature-dependent physical properties and heat transfer augmentation by complex flow. In addition, velocity and temperature profiles were measured under the coexistence of turbulent and drag-reducing flow in order to clarify the effect of drag reduction. It was confirmed that the drag reduction state was changed and diminished due to the temperature rise near the wall, especially the condition in the region of 50<y⁺<100 greatly influence on drag reduction of pipe flow.     

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.     

Magnetohydrodynamic chemically reactive viscoelastic fluid flow through an inclined porous layer

Analysis of a time-independent magnetohydrodynamic viscoelastic fluid flow in a deformable inclined porous layer with first-order chemical reaction has been investigated. Walters' fluid model has been used to study viscoelastic fluid. The walls are suctioned/injected at a constant rate. The expression representing the solution for solid displacement, fluid velocity, temperature, and concentration distribution is obtained. The effect of applicable parameters on solid displacement, fluid velocity, temperature, and concentration are discussed graphically, while skin friction, heat transfer, and mass transfer are revealed in a tabular structure. It is noticed that solid displacement, fluid velocity, and temperature profiles decrease when the viscoelastic parameter increase. Solid displacement enhances and the velocity of the fluid reduces owing to the influence of increasing drag parameter, whereas the reverse effect is seen for the volume fraction parameter. Nusselt number at the walls shows the opposite behavior for the viscoelastic parameter and Eckert number. Sherwood number at the walls shows opposite behavior for Reynolds number, Schmidt number, and radiation parameter. Also, the entropy generation number rises as a result of the influence of viscoelasticity and Eckert number.     

Experimental investigation on the thermal conductivity and shear viscosity of viscoelastic-fluid-based nanofluids

Viscoelastic-fluid-based nanofluids with dispersion of copper (Cu) nanoparticles in viscoelastic surfactant solution (aqueous solution of cetyltrimethylammonium chloride/sodium salicylate) were prepared. A comparative study of thermal conductivity and viscosity between viscoelastic-fluid-based Cu nanofluids and distilled water based nanofluids was then performed experimentally. Different concentrations of viscoelastic base fluid and volume fraction of Cu nanoparticles were matched in order to check their influences on fluid’s thermal conductivity and viscosity. The experimental results show that the viscoelastic-fluid-based Cu nanofluids have a higher thermal conductivity than viscoelastic base fluid, and its thermal conductivity increases with increasing temperature and increasing particle volume fraction. Furthermore, the viscoelastic-fluid-based Cu nanofluid shows a non-Newtonian behavior in its viscosity, and the viscosity increases with the increase of Cu nanoparticle concentration and decrease of temperature.     

紫铜管中聚丙烯酰胺水溶液抗剪切特性

本文对聚丙烯酰胺（PAM）水溶液在紫铜管内流动的减阻特性进行了实验研究,得到了PAM水溶液的减阻百分比随温度、浓度的变化情况。特别是针对暖通空调水系统的常见流动状态建立了抗剪切循环实验台,来研究PAM水溶液的抗剪切特性,为减阻剂PAM应用于工程实际,以便起到节约水泵能耗的作用,提供了有益的参考。     

Drag-reducing and heat transfer characteristics of a novel zwitterionic surfactant solution

Experiments were conducted to study the drag-reduction and heat transfer performances of a newly synthesized zwitterionic surfactant solution (oleyl trimethylaminimide) in a two-dimensional channel. For testing the drag-reduction at subzero temperatures, a 20% ethylene glycol aqueous solution (EG/W) was used as solvent. The surfactant concentration ranged from 50 to 1000 ppm and the temperature was ?5 and 25 °C, respectively. It was found that the novel zwitterionic surfactant solution showed both drag and heat transfer reduction characteristics, which were affected by concentration and temperature. The maximum drag-reduction was 83% at 25 °C for 200 ppm surfactant solution. The effects of addition of NaNO₂ to the surfactant solution were also investigated. For enhancing heat transfer of the surfactant drag-reducing flow, a destructive device, named Block, was designed and used in the experiments. The Block device has two contracting–expanding flow passages on both sides respectively with the central part blocked. It was found that the Block device can enhance the heat transfer performance of the novel zwitterionic surfactant solution to some extent while having a very small pressure drop penalty compared with other researcher’s destructive devices due to the dominant action of elongational stress.     

Entropy analysis in MHD Couette flow of chemically reacting viscoelastic fluid past a deformable porous channel

Here, an investigation of MHD Couette flow of a chemically reacting viscoelastic fluid past a deformable porous layer with entropy generation using Walters liquid model has been considered. A binary, homogeneous, and isotropic mixture of fluid and solid phases in the porous medium is considered. The impact of heat source parameter and Soret effect are taken into account. The governing equations are solved analytically to obtain the expressions for solid displacement, fluid velocity, temperature, and concentration. The impact of relevant parameters on the flow system, temperature, concentration, mass transfer flux, entropy generation number, and Bejan number are discussed graphically. It is observed that solid displacement enhances due to the growth of drag and viscoelastic parameter, while it reduces due to rising volume fraction parameter. Fluid velocity rises when the volume fraction parameter increases. Rising Brinkmann number enhances the temperature, while Brinkmann number and Soret number reduces the species concentration. The irreversibility of heat transfer dominates the flow near the channel plates, while the effect of fluid friction irreversibility can be observed within the channel centerline region.     

An impact of heat and mass transpiration on magnetohydrodynamic viscoelastic fluid past a permeable stretching/shrinking sheet

The present paper investigates analytically a continuous stream of viscoelastic fluid and magnetohydrodynamic flow of second-grade fluids owing to protracted sheets in a permeable medium with the help of the Cattaneo–Christov pattern. This idea is a new generalization of the classical Fourier law. Also, in this analysis, heat as well as mass transfer in second-grade fluid past wall suction/injection is assumed. A few similarity transformations are used to simplify the addressing of boundary layer expressions. An analytical solution is obtained by applying the Appell hypergeometric properties. Furthermore, our work also describes an effect of the relaxation time variable, elasticity number, and Prandtl number together with temperature fields. Also, we studied the newly introduced parameter, that is, the thermal radiation parameter by Cattaneo, over a Fourier heat flux pattern. In addition, some physical presentation of the measurements is illustrated in the graphs.