Quantitative visualization of oil-water mixture behind sudden expansion by high speed camera

The present work describes the application of an image processing technique to study the two phase flow of high viscous oil and water through a sudden expansion. Six different operating conditions were considered, depending on input volume fraction of phases, and all of them are resulting in a flow pattern of the type oil dispersion in continuous water flow. The objective is to use an optical diagnostic method, with a high speed camera, to give detailed information about the flow field and spatial distribution, such as instantaneous velocity and in situ phase fraction. Artificial tracer particles were not used due to the fact that oil drops can be easily distinguished from the continuous water phase and thus they can act as natural tracers. The pipe has a total length of 11 meters and the abrupt sudden expansion is placed at a distance equal to 6 meters from the inlet section, to ensure that the flow is fully developed when it reaches the singularity. Upstream and downstream pipes have 30 mm and 50 mm i.d., respectively. Velocity profiles, holdup and drop size distribution after the sudden expansion were analyzed and compared with literature models and results

Experimental and numerical characterization of multiphase subsurface oil release

Subsurface oil release is commonly encountered in the natural environment and engineering applications and has received the substantial attention of researchers after the disastrous Deepwater Horizon Blowout oil spill in 2009. The main focus on the present research is to systematically study the hydrodynamics of underwater oil jet under a variety of conditions, including the effect of dispersant and different gas to oil ratios (GOR) by using experimental measurement as well as a Computational Fluid Dynamics (CFD) approach, from which the measured turbulent characteristics (e.g., velocity, turbulent kinetic energy, turbulence dissipation rate, etc.) of underwater oil jet are thoroughly examined and compared. A Lagrangian Particle Tracking Model that coupled with CFD data is used to simulate the trajectories and movement of individual oil droplets under the effect of turbulence and comprehensive physical forces. The trajectories of oil droplets can be very different depending on the droplet diameter and physical force condition, which may bring insight into understanding the fate of oil droplets after the oil release. Large Eddy Simulation (LES) suggests that the oil and gas jet in the Deepwater Horizon Blowout can be churn rather than bubbly, which provides new perspectives on the estimation of the total oil flow rate during the blowout as well as the evaluation of dispersant effectiveness. Furthermore, a laboratory scale multiphase jet experiment by using Particle Imaging Velocimetry (PIV) as well as CFD simulation is conducted to understand and compare the hydrodynamics between the bubbly and churn jets, which shows that the churn jet may result in more entrainment from the ambient environment compared with the bubbly jet

Dynamics of liquid-liquid flows in horizontal pipes using simultaneous two-line planar laser-induced fluorescence and particle velocimetry

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

A PIV investigation of the effect of disperse phase fraction on the turbulence characteristics of liquid-liquid mixing in a stirred tank

In this paper, utilising 2D angle-resolved particle image velocimetry (PIV), the flow field of a dilute aqueous-in-oil dispersion is experimentally studied in a stirring tank. Opacity during liquid–liquid mixing is eliminated by matching the refractive indices of both phases. Anisotropy of the turbulence flow field is analysed via the turbulent kinetic energy (TKE) and energy dissipation rate (EDR) obtained at different measuring angles. The influence of spatial resolution is compared and discussed. TKE and EDR are observed to increase with increment of dispersed phase fraction while a small range of disorder and fluctuation is observed in the impeller region. The effect of dispersed droplets should be attributed to the strengthened fluctuation of velocities and spatial differences. Further work concerning higher resolution and the disperse fraction is necessary

A simultaneous planar laser-induced fluorescence, particle image velocimetry and particle tracking velocimetry technique for the investigation of thin liquid-film flows

AbstractA simultaneous measurement technique based on planar laser-induced fluorescence imaging (PLIF) and particle image/tracking velocimetry (PIV/PTV) is described for the investigation of the hydrodynamic characteristics of harmonically excited liquid thin-film flows. The technique is applied as part of an extensive experimental campaign that covers four different Kapitza (Ka) number liquids, Reynolds (Re) numbers spanning the range 2.3–320, and inlet-forced/wave frequencies in the range 1–10Hz. Film thicknesses (from PLIF) for flat (viscous and unforced) films are compared to micrometer stage measurements and analytical predictions (Nusselt solution), with a resulting mean deviation being lower than the nominal resolution of the imaging setup (around 20μm). Relative deviations are calculated between PTV-derived interfacial and bulk velocities and analytical results, with mean values amounting to no more than 3.2% for both test cases. In addition, flow rates recovered using LIF/PTV (film thickness and velocity profile) data are compared to direct flowmeter readings. The mean relative deviation is found to be 1.6% for a total of six flat and nine wavy flows. The practice of wave/phase-locked flow-field averaging is also implemented, allowing the generation of highly localized velocity profile, bulk velocity and flow rate data along the wave topology. Based on this data, velocity profiles are extracted from 20 locations along the wave topology and compared to analytically derived ones based on local film thickness measurements and the Nusselt solution. Increasing the waviness by modulating the forcing frequency is found to result in lower absolute deviations between experiments and theoretical predictions ahead of the wave crests, and higher deviations behind the wave crests. At the wave crests, experimentally derived interfacial velocities are overestimated by nearly 100%. Finally, locally non-parabolic velocity profiles are identified ahead of the wave crests; a phenomenon potentially linked to the cross-stream velocity field

Experimental and numerical heat transfer studies of nanofluids with an emphasis on nuclear fusion applications

A nanofluid is a mixture of a low concentration of solid particles (10-100nm in size at concentrations below 10%vol.) and a carrier fluid (usually conventional coolants). These novel fluids exhibit anomalous heat transfer phenomena which cannot be explained using classical thermodynamic models. The fluids can be designed to offer unsurpassed heat transfer rates for heat transfer related applications at low costs of manufacturing. This PhD thesis describes the efforts to test whether these fluids can be utilised for high heat flux applications (similar to those encountered in proposed future fusion reactors) and also to discover the mechanisms which give rise to the phenomenal heat transfer enhancements observed. A broad metadata statistical analysis was performed on published literature which provided qualitative results regarding the heat transfer enhancement to be expected from nanofluids, indicated trends connecting by part mixture properties and heat transfer enhancement values exhibited and provided probable explanations of the heat transfer mechanisms involved. This study was performed to tackle the novelty and scientific uncertainty issues encountered in the field. Optical laser diagnostics experiments were performed on a high heat flux device (HyperVapotron) in isothermal conditions. The study provided extensive information regarding the flow structures formed inside the device using conventional coolants and nanofluids. This helped to both, understand the conventional operation of the device as well as review probable suitable geometries for the utilisation of the device using nanofluids. Finally, a Molecular Dynamics Simulation code was composed to model heat conduction through a basic nanofluid. The code results suggested the formulation of a new type of complex heat transfer mechanism that might explain the augmentation of heat transfer encountered experimentally. A new low cost high throughput platform (HTCondor®) has been used to run the code in order to demonstrate the capabilities of the system for less financially able institutions.Open Acces

Hydrodynamic investigation of the discharge of complex fluids from dispensing bottles using experimental and computational approaches

The discharge of non-Newtonian, complex fluids through orifices of industrial tanks, pipes, dispensers, or packaging containers is a ubiquitous but often problematic process because of the complex rheology of such fluids and the geometry of the containers. This, in turn, reduces the discharge rate and results in residual fluid left in the container, often referred to as heel. Heel formation is undesired in general, since it causes loss of valuable material, container fouling, and cross-contamination between batches. Heel may be of significant concern not only in industrial vessels but also in consumer packaging. Despite its relevance, the research in this area is significantly limited. Previous research conducted in simpler systems, such as orifices of pipes and vessels, has already shown that the discharge of fluids through orifices is significantly affected by the geometric parameters and the fluid rheology. More specifically, the geometric properties of the orifice such as the diameter ratio, aspect ratio, and orifice shape, and the rheological properties of the fluid played a critical role on the discharge of complex fluids through orifices of vessels and pipes. However, how these parameters affect the discharge of complex fluids flow from more complicated systems such as consumer dispensing bottles operating with a hand pump has remained uninvestigated. Therefore, the overall objectives of this work are to quantify the discharge hydrodynamics in dispensing bottles and the resulting heel for a wide range of geometries, operational parameters, and fluid rheology through the use of experimental and computational approaches. Particle Image Velocimetry (PIV) is the main experimental tool used in this work. A novel experimental methodology is also developed and utilized to optimize the transparency of the highly complex fluids such as pastes, for their optical hydrodynamic investigations using PIV. In addition, Computational Fluid Dynamics (CFD) is also utilized to predict the hydrodynamics and the residual heel volume. The simulation predictions are validated against the experimental data. It is found that the heel volume and profile after the discharge is strongly related to the flow during the discharge, and both static and dynamic aspects of the discharge process can be determined using PIV, and predicted using CFD. Finally, correlations to predict the heel volume based on the rheological and geometric parameters are presented. It is expected that this work will be of significant academic and industrial interest, especially for product developers and packaging engineers to optimize the shape of dispensing bottles so that the discharge process from such containers is facilitated, and the heel volume is minimized