Characterization of drag reducing guar gum in a rotating disk flow

The turbulent drag reduction characteristics in a rotating disk apparatus were investigated by using polysaccharide guar gum in deionized water. The ultrasonic degradation method was adopted to obtain different molecular weight fractions of guar gum for this study. The stability of guar gum over time was observed to be better than the typical synthetic water‐soluble drag reducers [e.g., poly(ethylene oxide)]. A linear correlation between polymer concentration and the concentration/(drag reduction) for different molecular weights of guar gum was obtained, and the universal drag reduction curve for the guar gum/deionized water system was constructed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2938–2944, 2002; DOI 10.1002/app.10300     

Developing and fully developed turbulent flow of drag reducing fluids in an annular duct

Velocity profiles for the inner and outer flow regions of annuli are proposed for the turbulent flow of drag reducing fluids. Theoretical expressions for friction factors are developed. From the shear stress equations and the velocity profiles, estimates for the entrance lengths are given.     

减阻型纳米流体在圆管内的流动和换热特性

实验测定了在Reynolds数4000～16000范围内,质量分数0～0.5%的石墨、多壁碳纳米管、Al₂O₃、Cu、Al、Fe₂O₃、Zn纳米粒子加入到100～400 mg·kg^-1浓度的十六烷基三甲基氯化铵(CTAC)减阻剂中所制备的减阻型纳米流体的摩擦阻力系数和对流传热系数。结果表明:在CTAC中加入水杨酸钠(NaSal)与去离子水所配制的减阻剂具有一定的稳定性和很强的减阻特性,当减阻剂浓度为200 mg·kg^-1时其减阻特性最优。石墨纳米粒子在增强对流换热和减少流动阻力方面具有较佳的综合性能,当石墨纳米颗粒质量分数为0.4%时,其综合性能因子K是去离子水的5倍。最后给出了减阻型石墨纳米流体在圆管内的流动阻力和换热关联式,其计算值和实验值吻合良好。     

Review on the applications and developments of drag reducing polymer in turbulent pipe flow

Drag reduction phenomenon in pipelines has received lots of attention during the past decades due to its potential engineering applications, especially in fluid transporting industries. Various methods to enhance drag reduction have been developed throughout the years and divided into two categories;non-additives method and additives method. Both categories have different types of methods, with different formulations and applications which will generally be discussed in this review. Among all the methods discussed, drag reduction using polymer additive is as one of the most enticing and desirable methods. It has been the subject of research in this field and has been studied extensively for quite some time. It is due to its ability to reduce drag up to 80% when added in minute concentrations. Reducing drag in the pipe will require less pumping power thus offering economic relieves to the industries. So, this paper will be focusing more on the use of polymer additives as drag reducing agent, the general formulations of the additives, major issues involving the use of drag reducing polymers, and the potential applications of it. However, despite the extensive works of drag reduction polymer, there are still no models that accurately explain the mechanism of drag reduction. More studies needed to be done to have a better understanding of the phenomenon. Therefore, future research areas and potential approaches are proposed for future work.     

Pipeline scale-up in drag reducing turbulent flow

Models available in literature for predicting drag reduction scale-up are inadequate as they have been successful only over a narrow range of diameters. A new scale-up model is presented which equates dampening of turbulent velocity fluctuations by drag reducing additives to a reduction in the Prandtl mixing length. Flow and pressure drop data from a laboratory scale pipe along with shear viscosity measurements are sufficient to predict drag reduction scale-up in bigger diameter pipes. Using this approach, scale-up was successfully predicted over a diameter range of 7 to 154 mm for a surfactant-water system and 26.6 to 1194 mm for a polymer-oil system.     

Generalized correlation for friction loss in drag reducing polymer solutions

The definition of the pipe flow friction factor has been extended to include the effect of fluid viscoelastic properties on energy dissipation in turbulent tube flow. The resulting friction factor includes a characteristic fluid relaxation time, which can be determined directly from rheological measurements, and reduces to the usual Fanning friction factor for inelastic fluids. The use of this more general friction factor enables turbulent tube flow data for both fresh and shear degraded “concentrated” drag reducing polymer solutions of various concentrations in various tube sizes to be correlated by the usual f vs. N_Re relation for Newtonian fluids in smooth tubes.     

Characterization of drag reduction and degradation effects in the turbulent pipe flow of dilute polymer solutions

Turbulent drag reduction data were obtained at Re = 9000 in a 0.62-cm-I.D. pipe for five Polyox compounds covering a wide range of molecular weights. The concentration dependence of drag reduction was shown to obey an improved form of Virk's drag reduction equation, which was previously applied only to flows in capillary tubes. The efficiency of the drag-reducing polymer additives on a unit concentration basis at infinite dilution was determined by using a characteristic parameter, DR_m/[c], for each compound. A linear relationship was found to exist between this parameter and polymer molecular weight. The polymer degradation data were analyzed through use of a variable related to the dissipated energy in the wall region. The polymer molecular weight was found to decrease as a hyperbolic function of the dissipated energy function. By examining the change of molecular weight with respect to this function, a degradation index characteristic of the entire Polyox polymer family was established. This index may be of general application and provide a method by which the shear stability of various species of drag-reducing polymers may be meaningfully compared.     

Momentum/heat transfer analogy for drag reducing fluids during turbulent boundary layer flow with small pressure gradients

There have been many attempts in the literature to develop analogies for momentum, heat and mass transfer to drag reducing fluids; however, none have considered the presence of a pressure gradient when formulating the analogies. In the present work, a momentum/heat transfer analogy has been developed under the influence of small pressure gradient for drag reducing fluids using the Nakayama et al. (1984) solution methodology for Newtonian fluids. The results of the present analysis have been found to compare well with existing theoretical expressions.     

Bubble drag and mass transfer in non-newtonian fluids: Creeping flow with power-law fluids

The drag and mass-transfer characteristics of a gas bubble moving in power-law non-Newtonian fluids are examined analytically in terms of the rheological properties of the system. An approximate solution for the case of creeping flow around circulating bubbles shows that the mass-transfer coefficient is enhanced for pseudoplastics and depressed for dilatants compared to the situation for Newtonian fluids. Some preliminary experimental results in support of the analysis are presented.     

Drag reduction in large tubes and the behavior of annular films of drag reducing fluids

Turbulent flow drag reduction is governed by elastic effects within the boundary layer of the flow. The effect of elasticity is to reduce the radial momentum transfer rates of large eddies that exist near the tube wall, and in so doing a reduction in the turbulent flow drag occurs. A recent theoretical analysis is used to formulate a general discussion of the significant features of drag reducing systems and is used to predict quantitatively the percentage reductions in drag for systems of practical significance. It is shown that little or no drag reduction can be expected in large tubes using polymeric materials that are presently available though micellar systems show effects of substantial magnitude which appear to be exploitable. An analysis is presented which indicates that laminar annular films of dilute polymeric fluids, used to enable the core fluid or a capsule to “slide” through a pipeline at reduced pressure drop, are of especial interest in that the normal stress field may generate forces which increase the concentricity of the core in the presence of major density differences. This exploitation of non-Newtonian fluid properties, suggested some years ago by Lummus, does not appear to have been subjected to analysis before, nor do verifying experimental data appear to be available.     

疏水缔合聚合物湍流减阻特性影响因素

该文采用自行设计的气驱流体摩阻测试装置,研究了分子量、疏水单体比例和水解度对疏水缔合聚合物(HAWP)湍流减阻特性的影响;并且与ESEM观测不同质量浓度范围的HAWP水溶液的微观结构进行比对,讨论了HAWP的减阻机理。结果表明,当分子量大于1 000×104g/mol时,其减阻率在质量浓度为200 mg/L处和临界缔合质量浓度(CAC)处存在双峰值,对应两种不同的减阻机理;当分子量小于1 000×104g/mol时,仅在CAC处存在单一峰值;分子量越大第一峰值越高,分子量越小第二峰值越高。质量浓度小于CAC时,HAWP疏水单体比例越大,减阻率越小;而随着质量浓度的增大,疏水单体比例越大的,减阻率上升越快;而当质量浓度大于CAC时,则出现疏水单体比例越大减阻率越高的现象。HAWP在实验质量浓度范围内,减阻率均随着水解度的增大而增大。     

Experimental research on drag reduction by polymer additives in a turbulent pipe flow

In order to investigate the effects of injection position on drag reduction as well as further the effects of polymer additives on turbulent structures, LDA measurements of turbulent pipe flows were conducted. The results show that the amount of drag reduction grows with the increase of the Reynolds number, and injecting the polymer at the centre of pipe is more effective than at the wall. Due to the addition of polymer solution, the axial, radial r.m.s. velocity fluctuations and Reynolds stress decrease over the entire pipe cross‐section, the time auto‐correlation coefficients of axial and radial velocity fluctuation at the centre of pipe decay more slowly, the number of spectrum peaks is decreased, and the peak shifts towards lower wave numbers. The results also reveal that, due to the addition of polymer solution, the large‐scale vortices are enhanced and small‐scale vortices are suppressed.     

Inhibition of diffusion controlled corrosion in pipelines by drag reducing polymers under turbulent flow conditions

The effect of adding carboxymethylcellulose drag reducing polymer on the rate of corrosion of aluminium tube through which sodium hydroxide solution flows, was studied by a weight loss technique. The variables studied were solution flow rate and polymer concentration. Reynolds number and polymer concentration were varied over the range 3500 to 30 000 and 10 to 500 ppm, respectively. Polymer addition was found to decrease the rate of corrosion by a maximum of 63% depending on polymer concentration and Reynolds number.Nomenclature Re Reynolds number - Solution density - d tube diameter - u solution viscosity     

Degradation of drag reducing polymers in aqueous solutions

The performance of drag reducing polymers in turbulent flow is restricted by their mechanical degradation. This study examines how the working fluid can affect the degradation behavior of diluted drag reducing polymeric solutions. Solutions having different proportions of tap water and de-ionized water served as the working fluids. Three commercially available water soluble polymeric agents, namely, an anionic copolymer of polyacrylamide, xanthan gum, and polyethylene oxide, were then added to these solutions. All experiments had identical flow rates corresponding to turbulent conditions in a laboratory scale pipe line. Variation of pressure drop in the pipe line was then measured for 2 hours. It was found that polymer degradation is accelerated in tap water solutions compared to that in de-ionized water solutions. However, this is dependent on the specification of the polymer used, namely, the molecular weight of the polymer and the rigidity of its molecular backbone. Furthermore, a new mathematical relation has been developed to investigate degradation of the polymers over time.     

Forced convection in cross flow of power law fluids over a tube bank

The forced convective heat transfer characteristics for incompressible power-law fluids past a bundle of circular cylinders have been investigated numerically. The cylinder-to-cylinder hydrodynamic interactions have been approximated via a simple cell model. The momentum and energy equations have been solved using a finite difference based numerical method for a range of physical and kinematic conditions. The role of the two commonly used thermal boundary conditions, namely, constant temperature or constant heat flux, on heat transfer characteristics has also been studied. Extensive numerical results elucidating the effect of shear-thinning viscosity on the values of Nusselt number have been obtained for Peclet numbers ranging from 1 to 5000, Reynolds number in the range 1-500, flow behaviour index 1?n?0.5 and three values of voidages, namely, 0.4, 0.5 and 0.6, typical of tubular heat exchangers and tube banks. Under all conditions, varying levels of enhancement in Nusselt number are observed due to shear-thinning behaviour. The surface averaged Nusselt number shows strong dependence on the values of voidage, power-law index, Reynolds and Peclet numbers. The paper is concluded by presenting comparisons with the scant experimental results available in the literature.     

Investigation on the influence of sulfonic substitution in polyacrylamides for minimizing drag in turbulent flow of slickwater fluids

The use of slickwater fluids for fracking is key for accessing unconventional shale/tight-sand reservoirs. To mitigate the frictional losses observed during the injection, drag reducers like sulfonated polyacrylamides (SPAMs) are added to the slickwater fluids. The current study presents a unique controlled investigation that examines the impact of sulfonic group substitution, ranging from 5 to 25 wt%, in SPAMs. The molecular weight of the polymers is kept constant at ~7.5–7.8 million Daltons. The investigation is two-pronged: first part is comprised of drag reduction (%DR) performance of the polymers in fluids of varying salinities on a laboratory flow-loop. The results obtained indicated the inter-dependence of fluid salinity and sulfonic substitution on the polymer performance; for example, %DR deterioration of SPAM with 5 wt% substitution was 24.7%; to the contrary, the deterioration was only 15.6% for SPAM with 25 wt% substitution with rise in fluid salinity from 150 ppm to 110 k ppm. The second part of study included in development of a physics-based model where the polymer relaxation response (Weissenberg number) was improvised to accommodate the impact of governing parameters and then, successfully correlated with the %DR performance using phenomenological equations for the studied range of parameters.     

减阻剂的研究现状及应用

介绍了减阻剂的国内外研究与应用现状,综述了减阻剂的生产工艺,并对减阻剂今后发展方向提出了建议。     

The drag and pressure drops for hydrodynamically suspended cylinders in a vertical tube with and without polymer addition

The pressure drops and the suspension velocities for hydrodynamically suspended aluminum and steel cylindrical bodies were measured for a range of aspect ratios (L/d) in a 5 cm vertical plexiglass tube. Four different body-to-tube diameter ratios (d/D) from 0.432 to 0.864 were investigated. Both water and drag reducing aqueous polymer solutions of Reten 423^* having concentrations in the range 20 to 100 ppm by weight were used. In all cases, the addition of polymer reduced the drag coefficient and the drag coefficient per aspect ratio approached a constant value as (L/d) approaches 14. The available data for cylindrical bodies in vertical pipelines were correlated to obtain semi-empirical equations relating pressure drops, drag coefficients and suspension velocities.     

圆管聚合物热流中黏性耗散分析的无网格模拟

以与温度相关的指数定律作为本构方程,应用无网格方法模拟了外表面为恒温时的圆管内具有黏性耗散的聚合物流动热传导问题,给出了离入口不同位置处的温度分布。计算结果表明：根据黏性耗散模型计算的温度比无黏性耗散模型高出64℃,从而说明了黏性耗散在聚合物流动热传导问题中具有举足轻重的作用。并且, 无论是无黏性耗散模型,还是黏性耗散模型,其极限温度与壁面温度有很大的关系,但与入口温度无关。