LDA measurements of non-Newtonian liquids in pipe flow

Journal of Non-Newtonian Fluid Mechanics, 2005

The purpose of this brief paper is to report mean velocity profile data for fully developed pipe flow of a wide range of shear-thinning liquids together with two Newtonian control liquids. Although most of the data reported are for the laminar-turbulent transition regime, data are also included for laminar and turbulent flow. The experimental data were obtained in unrelated research programmes in UK, France and Australia, all using laser Doppler anemometry (LDA) as the measurement technique. In the majority of cases, axisymmetric flow is observed for the laminar and turbulent flow conditions, although asymmetry due to the Earth's rotation is evident for the laminar flow of a Newtonian fluid of low viscosity (i.e. low Ekman number). The key point, however, is that for certain fluids, both yield-stress and viscoelastic (all fluids in this study are shear-thinning), asymmetry to varying degrees is apparent at all stages of transition from laminar to turbulent flow, i.e. from the first indications to almost fully developed turbulence. The fact that symmetrical velocity profiles are obtained for both laminar and turbulent flow of all the non-Newtonian fluids in all three laboratories leads to the conclusion that the asymmetry must be a consequence of a fluid-dynamic mechanism, as yet not identified, rather than imperfections in the flow facilities.

2024

This experimental study focuses on exploiting laser Doppler velocimetry (LDV), a non-intrusive technique, for rheological characterization based on analyzing flows of Carbopol solutions at two distinct concentrations and two different temperatures within a pipe. The velocity profiles obtained using LDV and the pressure drops associated with each flow rate were exploited to establish the behavioral law of aqueous Carbopol solutions. Two approaches were used: the first was an analytical velocity model to fit the experimental profile, and the second used the first derivative of the experimental velocity profile and the pressure drops to reconstruct the flow curve. In addition, a third reference characterization was carried out using a rotary rheometer equipped with a vane geometry. This study's three rheological characterization methods showed excellent agreement concerning the Herschel-Bulkley model. Finally, all the laws resulting from these three methods were validated using an empirical law relating to Darcy's coefficient of friction.

International Journal of Multiphase Flow, 2018

Experimental investigations are reported of stratified and stratified-wavy oil-water flows in horizontal pipes, based on the development and application of a novel simultaneous two-line (two-colour) technique combining planar laser-induced fluorescence with particle image/tracking velocimetry. This approach allows the study of fluid combinations with properties similar to those encountered in industrial field-applications in terms of density, viscosity, and interfacial tension, even though their refractive indices are not matched, and represents the first attempt to obtain detailed, spatiotemporally-resolved, full 2-D planar-field phase and velocity information in such flows. The flow conditions studied span mixture velocities in the range 0.3-0.6 m/s and low water-cuts up to 20%, corresponding to in situ (local) Reynolds numbers of 1750-3350 in the oil phase and 2860-11,650 in the water phase, and covering the laminar/transitional and transitional/turbulent flow regimes for the oil and water phases, respectively. Detailed, spatiotemporally-resolved in situ phase and velocity data in a vertical plane aligned with the pipe centreline and extending across the entire height of the channel through both phases are analysed to provide statistical information on the interface heights, mean axial and radial (vertical) velocity components, (rms) velocity fluctuations, Reynolds stresses, and mixing lengths. The mean liquid-liquid interface height is mainly determined by the flow water cut and is relatively insensitive (up to 20% the highest water cut) to changes in the mixture velocity, although as the mixture velocity increases the interfacial profile transitions gradually from being relatively flat to containing higher amplitude waves. The mean velocity profiles show characteristics of both laminar and turbulent flow, and interesting interactions between the two co-flowing phases. In general, mean axial velocity profiles in the water phase collapse to some extent for a given water cut when normalised by the mixture velocity; conversely, profiles in the oil phase do not. Strong vertical velocity components can modify the shape of the axial velocity profiles. The axial turbulence intensity in the bulk of the water layer amounts to about 10% of the peak mean axial velocity in the studied flow conditions. In the oil phase, the axial turbulence intensity increases from low values to about 10% at the higher Reynolds numbers, perhaps due to transition from laminar to turbulent flow. The turbulence intensity showed peaks in regions of high shear, i.e., close to the pipe wall, and at the liquid-liquid interface. The development of the mixing length in the water phase, and also above the liquid-liquid interface in the oil phase, agrees reasonably well with predicted variations described by the von Karman constant. Finally, evidence of secondary flow structures both above and below the interface exists in the vertical velocity profiles, which is of interest to explore further.

Physical Review E, 2011

The flow of polymer solutions is examined in a flow geometry where a jet is used to inject the viscoelastic solution into a cylindrical tube. We show that this geometry allows for the generation of a "turbulentlike" flow at very low Reynolds numbers with a fluctuation level which can be as high as 30%. The fluctuations increase with an increase in solution polymer concentration and flow velocity. The turbulent fluctuations decay downstream for small flow velocities but persist for high velocities. The statistical properties of the generated fluctuations indicate that this turbulentlike flow is different from previously studied flows displaying elastic turbulence and shows a direct cascade of energy to small scales with practically no intermittency.

AIChE Journal, 1967

An optical technique for the quantitative determination of point velocities in ropidly developing laminar flows of transparent liquids is useful as an experimental tool in problems of complex geometries and fluids. The accuracy of the technique has been confirmed by comparison of experimental data with the numerical solution of the equation of motion for the entrance region problem. A distributor copable of generating a flat velocity profile has been developed for this purpose.

International Journal of Multiphase Flow, 2013

This paper describes a set of experiments on liquid-liquid flows in a horizontal circular tube. The liquids used in the experiments were an aliphatic hydrocarbon oil (Exxsol D80) and an aqueous solution of glycerol. The concentration of glycerol in the solution was adjusted so that the two liquids had the same refractive index, and optical distortions due to the curvature of the (transparent) circular tube test section were corrected for with the use of a graticule technique. The test section was far downstream of an inlet section that established an initially stratified co-current flow of the two immiscible liquids, with the Exxsol D80 oil flowing over the glycerol/water solution. The flows were investigated at the test section with the application of laser-based optical diagnostic methods, which included high-speed simultaneous Planar Laser Induced Fluorescence (PLIF), Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV). These techniques allowed the reliable evaluation of the nature of the investigated * Corresponding author. Page 2 of 39 horizontal liquid-liquid flows (i.e., the flow patterns from phase distribution information), together with the detailed spatiotemporally resolved measurement of key flow characteristics such as phase and velocity distributions, and also of important parameters such as droplet size. The resulting PLIF images provide a clear indication of the distribution of the phases within a plane that passed through the channel centreline, and are used to obtain qualitative information about the arising flow patterns. The images were also used quantitatively to generate data on phase distribution, in-situ phase fraction, interface level and droplet size distribution. Much of the PLIF data on in-situ phase fraction and interface level agrees well with predictions from a simple stratified laminar-laminar flow model. The particle velocimetry methods (PIV and PTV) provide data on the velocity profiles in the investigated flows. Over the range of superficial velocity conditions investigated, the velocity profile in the lower (heavier and more viscous) glycerol/water solution phase was typically characteristic of laminar flow, whereas in the upper (lighter and less viscous) Exxsol D80 oil phase the profile often showed a shape characteristic of turbulent flow. Horizontal liquidliquid pipe flows Morgan, Markides, Zadrazil and Hewitt fluorescence (PLIF). Liu (2005) reports a study of vertical downflow of liquid-liquid flow mixtures using PLIF and, more recently, Morgan, et al. (2012) reported the application of the technique to horizontal liquid-liquid flows. Though the studies of Liu (2005) and Morgan, et al. (2012) revealed a number of

Physics of Fluids, 1994

Some measurements have been obtained for the axial velocity of the fully developed laminar flow in a circular straight pipe with radius a, which is rotating with constant angular speed fi about an axis perpendicular to its own axis. A diode laser LDA system was mounted together with a circulating pipe flow system on a rotating table for the experiment. According to previous analyses and calculations, there exist four types of axial velocity distributions that result from the various effects of the secondary fiow on the main stream via the convection and Coriolis effect for different values of R( = w&/v) and R,(=&"/v), where W; is the mean axial velocity and v is the kinematic viscosity of the fluid. The present study provides experimental validation for the previous theoretical and numerical analyses. Experiments have also been carried out for studying the asymptotic nature of the slow flow in a rapidly rotating pipe (R@l and RnSR) and the rapid flow in a slowly rotating pipe (RR,&1 and R%R,).

1997

A non-invasive experimental technique which enables optical penetration into the bulk of a flowing liquid-solid concentrated suspension was employed to study such flows. Matching of refractive indices of the continuous and dispersed phases was used to establish optimal conditions for the quality of the optical signals and can be used to measure concentration in the flowing dispersion. Laser-Doppler anemometry was applied to measure velocity profiles in a rectangular duct and to detect velocity fluctuations in the viscous flow of the concentrated suspension induced by the particles presence. The existence of a net drift of particles in a concentrated suspension is demonstrated.

English: Experimental investigations were carried out in pipe flow of Newtonian and Non Newtonian fluids. The investigations of Newtonian flow were focused on the origin of laminar turbulent intermittency in the flow. It was found that upon reduction of the Reynolds number starting from fully turbulent flows laminar regions appear randomly. Unlike reported for other shear flows there was no wavelength induced instability in pipe flow. The development of intermittent patterns and in particular the minimum spacing between turbulent puffs is shown as a consequence of an interaction between neighboring puffs which has been identified. The puff interaction distance is found to decrease with increase in Re and it is in quantitative agreement with minimum spacing of plane Couette and Taylor Couette flow.

A hybrid multi-scale velocimetry method utilizing Doppler optical coherence tomography in combination with either magnetic resonance imaging or ultrasound velocity profiling is used to investigate pipe flow of four rheologically different working fluids under varying flow regimes. These fluids include water, an aqueous xanthan gum solution, a softwood fiber suspension, and a microfibrillated cellulose suspension. The measurement setup enables not only the analysis of the rheological (bulk) behavior of a studied fluid but gives simultaneously information on their wall layer dynamics, both of which are needed for analyzing and solving practical fluid flow-related problems. Preliminary novel results on rheological and boundary layer flow properties of the working fluids are reported and the potential of the hybrid measurement setup is demonstrated.