Synthesis and performance evaluation of a new drag reducer based on acrylamide/12-allyloxydodecyl acid sodium

Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters.     

Diameter dependence of the cutoff molecular weights of drag-reducing polymers

Drag reduction data of poly(ethylene oxide) obtained in turbulent pipe flows were analyzed. A cutoff molecular weight for drag reduction was determined by correlating the drag reduction effectiveness with polymer molecular weight. Based on a time-correlation onset concept, this critical molecular weight was found to depend on the pipe diameter and Reynolds number. This effect is examined using available experimental data.     

Turbulent flow behaviour of dilute polymer solutions in an annulus

An experimental study has been carried out to investigate the turbulent flow behaviour of dilute polymer solutions in an annulus. The polymers used are two grades of Separan, AP30 and MG500, both are known to exhibit drag reduction characteristics in turbulent pipe flow. Similar drag reduction phenomena have been observed in annulus flow. At a given Reynolds number, the friction factor decreases with increase in polymer concentration and appears to reach a minimum (or maximum drag reduction) at certain optimum concentration. An estimate of the critical wall shear stress, which marks the onset of drag reduction, is consistent with pipe flow results, suggesting that the critical value is independent of flow geometry and size. A lower drag reduction, achieved in an annulus in comparison with circular pipes, is attributed mainly to a diameter effect.     

非离子表面活性剂的加入对水基纳米微流体在小直径管中的减阻作用(英文)

The goal of this research was to determine the impact of nonionic surfactants on drag reduction effect in water and metal oxide nanofluid. Two nonionic surfactants (Rokacet O7 and Rokanol K7) and copper(Ⅱ) oxide water-based nanofluid were examined. Friction factors in a 4 mm diameter pipe for the Reynolds number between 8000 and 50000 were determined. Results showed that addition of nonionic surfactants caused the decrease of friction factor in water and nanofluid. The drag reduction effect was similar in both cases. Presence of nanoparticles in the system has no great influence on drag reduction effect.     

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.     

The Use of Drag Reduction Agent and a Detergent for Drag Reduction in Circulatory Vertical Pipe Flow

This paper describes the results of an experimental study of drag reduction in a circulatory vertical pipe system for both upward and downward flows using a drag reduction agent, corrosion inhibitor, and a cheap detergent (washing-up liquid) with various concentrations for different flow rates.

It was found that the corrosion inhibitor did not produce any drag reduction effect for both upward and downward flows while the drag reduction agent was effective for both flows; whereas, the detergent was effective only for upward flow. A comparison of the effectiveness of the drag reduction agent against the detergent showed that the effectiveness of the drag reduction agent is much higher than that of the detergent. The effect of liquid detergent is only noticeable if a large concentration is used. A 1000-ppm of detergent produces the same results as 25 ppm of drag reduction agent, which undermined the lower cost of the detergent. Over the range of Reynolds numbers tested the maximum drag reduction for upward flow is 35% while for the downward flow is 42%.     

On the link between experimentally-measured turbulence quantities and polymer-induced drag reduction in pipe flows

In this study, we investigate the hydrodynamics of polymer-induced drag reduction (DR) in horizontal turbulent pipe flows. We provide spatiotemporally resolved information of velocity and its gradients obtained with particle image velocimetry measurements in solutions of water with dissolved polyethylene oxide of three different molecular weights (MWs), at various dilute concentrations and with flow Reynolds numbers from 35,000 to 210,000. We find that the local magnitudes of important turbulent flow variables correlate with the measured levels of DR irrespective of the flow Reynolds number, polymer weight, and concentration. Contour maps illustrate the spatial characteristics of this correlation. A relationship between the DR and the turbulent flow variables is found. The effects of the polymer MW, its concentration, and the Reynolds number on the flow are further examined through joint probability distributions of the fluctuations of the streamwise and spanwise velocity components.     

Some Experimental Aspects of Drag Reduction in Thermoplastic Pipes

This paper reports some experimental results of using a new additive solution for reducing drag in thermoplastic pipes. It was found that the amount of drag achieved is very much dependent on the diameter of the pipe, Reynolds number, and concentrations of the additives. In general it was found that the drag is higher in small-diameter thermoplastic pipes. The maximum drag reduction obtained was 29.4%.     

Experimental correlation for pipe flow drag reduction using relaxation time of linear flexible polymers in a dilute solution

In this study, we investigate the drag reduction property of a linear flexible polymer, PEO (polyethylene oxide) in a fully turbulent pipe flow. The aim of this study is to develop a correlation to predict the drag reduction using the Weissenberg number, a dimensionless number related to the relaxation time of the polymer and the polymer concentration in dilute solutions. The physical meaning of the relaxation time of polymers and overlap concentration between the dilute and semi-dilute polymer solution are clarified. A higher polymer concentration, Reynolds number, and Weissenberg number lead to an increasing drag reduction. A semi-empirical correlation to predict the drag reduction with two dimensionless variables mentioned above is established and can predict the experimental data in this work and other previous works well. Previous correlations that use Reynolds number often require high flow velocity or large pipes in the experimental setup to predict drag reduction in large-scale industrial applications, which involves extra cost and potential safety issues. The current new correlation method uses relatively low velocities to avoid the problems mentioned above.     

THE EFFECT OF HETEROGENEOUS DRAG REDUCING SURFACTANT IN DRAG AND HEAT TRANSFER REDUCTION IN CRUDE OIL SYSTEMS

Pilot scale experiments have been performed to study the effect of a heterogeneous surfactant into the drag and heat transfer coefficient in crude oil pipelines. The effects of surfactant concentration, pipe diameter, Reynolds number and temperature were studied in this research program.

An extensive set of data was obtained for heat transfer and friction coefficients for a heterogeneous surfactant known as MDR-2000. A wide range of Reynolds numbers were covered and experiments were conducted for many different Prandtl numbers. All drag and heat transfer reduction experiments were performed in the same installation using the same measurement techniques which facilitates the assessment of the trends caused by the various parameters studied.

Typical results showed that the friction coefficient was reduced by half at the optimum concentration. While, the heat transfer coefficient was reduced even more dramatically.     

Wasserlösliche hochpolymere als strömungsbeschleuniger

Soluble high polymers drastically reduce the friction or drag of turbulent wall flows; this effect is widely known as drag reduction. In practical applications drag reducing polymers also bring about an increase in flow rate. That is why we have introduced the term flow enhancer for this type of polymer. Drag reduction by polymers was discovered in 1948. The addition of very small amounts (ppm) of a high polymer reduces the pressure drop in turbulent pipe flow by up to 80 % or increases the flow rate by up to 100 %. These rheological effects are demonstrated with the aid of laboratory experiments. A physical model is presented which describes the interference of the coiled macromolecule in turbulent boundary layers with elongational velocity gradients. From this theory are derived a number of requirements for particularly effective macromolecules, such as molar mass, conformation, linearity and electrical charges in the molecule. The well-known water soluble drag reducing polymers are presented and the influence of pH, electrolytes and temperature described. Finally a survey of practical applications with experiments describing the operation of a specially designed flow enhancer for hydrotransport of sand slurries is given.     

Drag reduction in cocurrent horizontal natural gas-hexane pipe flow

Drag reduction in two-phase cocurrent horizontal natural gas-hexane pipe flow was studied experimentally. The effects of pipe diameter, gas flow rate, liquid flow rate, and additive concentration were investigated using the Dowell APE drag reducer. In the annular-mist flow regime studied, it was found that drag reduction increased with decreasing gas rate for a given liquid rate, drag reduction decreased with increasing friction velocity and it decreased with decreasing gas-liquid ratio for a given friction velocity. Although the drag reduction decreased rapidly as the liquid-gas ratio approached zero, drag reductions as high as 34 percent were obtained. Attempts to predict two-phase drag reduction were unsuccessful as it was found to depend upon friction velocity, liquid and gas rates, liquid-gas rate ratio, pipe diameter and additive concentration.     

壁面微沟槽与表面活性剂耦合对管道中湍流减阻特性的影响

通过矩形管道压降实验研究了壁面微沟槽和表面活性剂的减阻性能及联合减阻的增益效果,用粒子成像测速仪分析了流场特性。实验所用的微沟槽为3种不同结构的顺流向V形沟槽,表面活性剂为十六烷基三甲基氯化胺(CTAC),水杨酸钠(NaSal)作为补偿离子。结果表明,壁面微沟槽和表面活性剂溶液均有减阻效果,二者耦合后减阻率进一步提升,最高减阻率为48.26%。微沟槽的减阻性能主要作用在近壁区,通过影响边界层平均流速、速度脉动强度和涡结构,减少表面活性剂的湍动能损耗。当超过表面活性剂的临界雷诺数后,沟槽尖端的高剪切力会加剧胶束结构分解。表面活性剂能抑制湍流涡的演变,扩大微沟槽有效减阻的雷诺数范围。     

微流道粗糙壁面对流动阻力和控制的影响

研究了3种粗糙单元(三角形、矩形、三角形与矩形交错混合)壁面对微流道内流动和摩擦阻力的影响。利用二维模型模拟了量纲一泊肃叶数与粗糙单元的几何特性和分布的关系。结果发现:在模拟条件下,粗糙壁面摩擦阻力(泊肃叶数)总是大于光滑壁面的摩擦阻力;壁面粗糙单元的高度对摩擦阻力的影响较大,可有近乎指数型的增长,粗糙单元的长度和间隔的影响居中,而雷诺数的影响较小。说明壁面粗糙度可有效改变槽道内的流动状态,增大混合效率。     

低粘附功管壁的内流减阻研究

以乙烯基三乙氧基硅烷 无水乙醚溶液处理玻璃管道内壁 ,降低流体水与管壁间的粘附功 ,研究了低粘附功内壁管道的内流减阻性能。结果表明 ,在管壁与液体间的粘附功小于液体的内聚功条件下 ,当雷诺数大于临界雷诺数时 ,低粘附功内壁管道呈现明显的内流减阻效果 ,临界雷诺数的值与一定的临界壁面剪力值或层流底层临界厚度值相对应 ;在减阻区内 ,减阻率随雷诺数的增加及管道内径的减小而增大 ,阻力系数的无因次关联式可表示为λ=f (Re ,X) ,其中X为无因次数群 [W / (du2 ρ) ]。     

Scaling functions of polymer‐induced turbulent drag reduction focusing on the polymer–solvent interaction

Based on turbulent drag reduction characteristics of polystyrene and polyisobutylene in a pipe flow and a rotating‐disk flow, respectively, a relationship between polymer concentration and drag reduction at a given Reynolds number was considered. The universal drag reduction equation of a three‐parameter relationship between drag reduction and polymer concentration was modified using intrinsic concentration and intrinsic viscosity, and it was then found to be the most useful formula for correlating DR data, especially for polymer–solvent interactions in a turbulent flow. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1836–1839, 2003     

Effect of contamination on rise velocity of bubble swarms at moderate Reynolds numbers

In this work, hydrodynamics of contaminated bubble swarms is numerically investigated using the free surface cell model combined with the spherical stagnant cap model. The governing field equations are solved numerically to elucidate the effect of Reynolds number, gas holdup and degree of contamination on the hydrodynamic behavior of bubble swarms. New extensive results are reported over the range of conditions as follows: Reynolds number, Re: 1–200, bubble holdup, Φ: 0.1–0.5, and stagnant cap angle, α: 0–180°. Finally, the effects of these parameters on streamlines and vorticity contours, surface pressure and vorticity distributions and on drag coefficients are discussed in detail. Briefly, the drag coefficients decrease with the decreasing stagnant cap angle and/or the decreasing bubble hold up and/or the increasing Reynolds number; whereas the ratio of the pressure and friction drag coefficients exhibits mixed trends with respect to these parameters.     

Effect of Helical Surface Disc Turbulators on Heat Transfer and Friction Factor Characteristics in the Annuli of a Double‐Pipe Heat Exchanger

The heat transfer and pressure drop characteristics in annuli of a double‐pipe heat exchanger (DPHE) using helical surface disc turbulators (HSDTs) are experimentally investigated. The effect of a helical surface disc turbulator is studied for three pitch ratios, three diameter ratios, and varying Reynolds numbers. Water flows in the inner tube and air through the annulus. The tests are conducted for air with uniform wall temperature condition. The heat exchanger with the least pitch ratio and least diameter ratio was found to exhibit the highest Nusselt number and pressure drop. The thermal performance factor turned out to be greater than unity for all cases. Correlations were developed for Nusselt number, friction factor, and thermal performance.     

Extension of Hill-Koch-Ladd drag correlation over all ranges of Reynolds number and solids volume fraction

Hill et al. [R. J. Hill, D.L. Koch, J.C. Ladd, J. Fluid Mech. (2001), 448, pp. 213-241 and 243-278] proposed a set of drag correlations, based on data from Lattice-Boltzmann simulations. These correlations, while very accurate within the range of void fractions and Reynolds numbers used in the Lattice-Boltzmann simulations, do not cover the full range of void fractions and Reynolds numbers encountered in fluidized bed simulations. In this paper a drag correlation applicable to the full range of void fractions and Reynolds numbers is developed by blending the Hill-Koch-Ladd (HKL) drag correlation with known limiting forms of the gas-solids drag function such that the blended function is continuous with respect to Reynolds number and void fraction. This study also corrects a misinterpretation of the HKL drag correlation that was published in the literature, which makes the drag function discontinuous with respect to the Reynolds number.Two examples of gas/solids flows in a bubbling fluidized bed and a one-dimensional channel flow are used to illustrate differences between the proposed extension of HKL drag correlation and another form published in the literature.     

Moving-bed solids flow between two fluidized beds

A simplified form of the macroscopic momentum balance for two-phase flow is applied to moving-bed solids flow in an inclined pipe connecting two fluidized beds. The resulting equation shows that the gravity force of the material in the pipe is counter-balanced by the pressure drop across the pipe and the wall friction. In order to account for the wall friction, a friction factor analogous to the Fanning friction factor in fluid flow is defined, and a friction factor correlation is established based on the data of Trees [11]. The friction factor is found to be a function of the solids flow rate and the pipe diameter.The flow curves of moving-bed solids were also constructed based on the data of Trees. The resulting straight lines show the power-law type flow behavior of the solids. And from the power law indices, it has been shown that the data fit well with the generalized friction factor correlation by Metzner and Reed [16]. It is also observed that data of different pipe diameters yield separate flow curves, which is unusual for time-independent fluids. However, the possibility that moving-bed solids may be time dependent can be ruled out because data of different pipe lengths do fall on a single line.