Drag Reduction Applications Research Articles

Experimental Study of DRA for Vertical Two-Phase Annular Flow

Experimental investigation of drag reduction in vertical two-phase annular flow is presented. The work is a feasibility test for applying drag reducing additives (DRAs) in high production-rate gas-condensate wells where friction in the production tubing limits the production rate. The DRAs are intended to reduce the overall pressure gradient and thereby increase the production rate. Since such wells typically operate in the annular-entrained flow regime, the gas and liquid velocities were chosen such that the experiments were in a vertical two-phase annular flow. The drag reducers had two main effects on the flow. As expected, they reduced the frictional component of the pressure gradient by up to 74%. However, they also resulted in a significant increase in the liquid holdup by up to 27%. This phenomenon is identified as “DRA-induced flooding.” Since the flow was vertical, the increase in the liquid holdup increased the hydrostatic component of the pressure gradient by up to 25%, offsetting some of reduction in the frictional component of the pressure gradient. The DRA-induced flooding was most pronounced at the lowest gas velocities. However, the results show that in the annular flow the net effect will generally be a reduction in the overall pressure gradient by up to 82%. The findings here help to establish an envelope of operations for the application of multiphase drag reduction in vertical flows and indicate the conditions where a significant net reduction of the pressure gradient may be expected.

Factors influencing adhesion of fluorocarbon (FC) thin film on silicon substrate

Hydrophobic polymeric thin films (e.g., fluorocarbon) are used in micro-fluidic applications for drag reduction. However, one of the major issues hindering their usage is reliability. Previous work shows a degradation/delamination of fluorocarbon (FC) film over a period of time. This paper investigates various processing parameters influencing the adhesion of hydrophobic FC coating to a silicon substrate. The FC film is processed using the “Bosch” process (alternating etching and deposition steps) to perform deep anisotropic silicon etching. The Si(100) wafers are first etched to a depth of about 5–10 μm and then coated with CF x film from the C 4F 8 monomer. The effect of pressure, inductively coupled plasma power, thickness of the film, and the gas ratio of mixing H 2 to C 4F 8 has been investigated using a fractional factorial experimental design. By better understanding the effect of each input variable, the reliability of the deposited film can be improved and this is discussed in detail in this paper.

210 界面活性剤による抵抗低減効果の実用化のための諸問題の検討(OS2-2 流れの抵抗低減(2),OS2 流れの抵抗低減,オーガナイズドセッション)

210 界面活性剤による抵抗低減効果の実用化のための諸問題の検討(OS2-2 流れの抵抗低減(2),OS2 流れの抵抗低減,オーガナイズドセッション)

Partial Cavitation as Drag Reduction Technique and Problem of Active Flow Control

Partial cavitation can substantially reduce the ship total drag in a wide range of her speed. Vented partial cavitation manifested certain advantages in comparison with other drag reduction techniques. Its successful employment, however, requires both a special hull design and development of an active flow control system. Such a system will stabilize the cavity under perturbations of incoming flow in seas. The paper includes an analysis of achievements in drag reduction, description of design fundamentals of ships with cavitating hulls/elements, and suggestions on application of ship drag reduction by cavitation.

Application of Surfactant Drag Reduction for Practical Air Conditioning Systems.

Many researches of drag reduction caused by cationic surfactants have been reported in recent years. However, there are few papers about the application of drag reduction for practical air conditioning systems. In this study, the effects of corrosion inhibitors on the drag reduction caused by a cationic surfactant, Ethoquad O/12, were experimentally investigated. Suitable corrosion inhibitors were proposed and significant change of rheological properties of surfactant solutions with the corrosion inhibitors was also indicated. Such drag-reducing additive was used for a practical air conditioning system, and the energy saving rates was experimentally obtained. Other ten examples of drag reduction adopted for practical systems were also presented in this paper.

1007 抵抗減少剤の空調システムへの応用

1007 抵抗減少剤の空調システムへの応用

On pipe diameter effects in surfactant drag-reducing pipe flows

Remarkable power saving in a fluid transport system is possible if the surfactant drag reduction technology is used. Application of surfactant drag reduction to district heating and cooling systems has been investigated in the past. The establishment of the scale-up law in drag-reducing pipe flows is one of the most important problems in this application. Main purpose of this study is aimed to develop a reliable scale-up law in surfactant drag-reducing flows. As the basic data of surfactant solutions, both non-Newtonian viscosity and viscoelasticity were experimentally determined. A turbulent eddy diffusivity model based on the Maxwell model was employed to estimate the drag reduction of surfactant solutions. The predictions by the turbulence model developed in this study with proper rheological characteristics of surfactant solutions has resulted in a reliable estimation of the pipe diameter effect in surfactant drag-reducing flows over the pipe diameter range from 11 to 150mm.

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.

Degradation effects of dilute polymer solutions on turbulent drag reduction in pipe flows

An important practical problem in the application and study of drag reduction by polymer additives is the degradation of the polymer, for instance due to intense shearing, especially in recirculatory flow systems. Such degradation leads to a marked loss of the drag-reducing capability of the polymer.

The Effect Of Drag Reducing Additives On Fluid Flows And Their Industrial Applications Part 2: Present Applications And Future Proposals*

This state of-the-art review is published in two parts: Part 1 has already appeared and deals with basic aspects of the subject, while this part sets out details of specific drag reduction applications. These include oil pipelines, oil well fracturing, sewers, open channels, hydropower penstocks and culverts, the hydrotransport of pulverised solids, the effect of drag reducing additives on fluid machinery, marine applications, their use in heating systems, firefighting and jet cutting. The preparation and injection of polymer solutions, the economics of their use, their degradation in flow and the pollution implications of their release into water courses are aslo covered. Wherever possible field test results are included and discussed. The bibliography contains 154 references to published material.

The langevin approach to the dumbbell kinetic problem in rheology

An alternative formalism to the dumbbell kinetic problem is proposed which is believed to be more fundamental than the classical Liouville one. The new formulation provides a logical approach to non-conservative systems and systems with varying frictional coefficients. A non-linear dumbbell with internal viscosity and varying frictional factor for the beads is examined. It is proved that the centre of gravity of the dumbbell must move affinely with the solvent continuum. A useful class of approximation is suggested to reduce the constitutive equation to an explicit form. The response of the model is computed for a number of flow fields. For shear flows, the introduction of the internal viscosity results in a shear-thinning phenomenon. The onset of non-Newtonian behaviour occurs at the correct order of magnitude of the dimensionless shear rate. Also, a negative second normal stress difference is found which varies with shear rate. In an oscillatory shear flow, the internal viscosity leads to a finite limiting value of the dynamic viscosity at high frequencies. In elongational flow the effects of the varying frictional coefficient dominate that of the internal viscosity. Interesting phenomena include the presence of a hysteresis loop and the ability of the dumbbell to maintain an extended configuration at moderate elongational rates. Clearly, these are relevant in turbulent drag reduction applications. The model has sufficient merits to deserve more investigation.