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

Abstract

a b s t r a c tExperimental 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.

Experimental investigations of upward-inclined stratified oil-water flows using simultaneous two-line planar laser-induced fluorescence and particle velocimetry

“…The experimental investigations were performed in the flow facility known as TOWER (Twophase Oil-Water Experimental Rig) located at Imperial College London, which is illustrated in 1. The same facility and test fluids were used in our earlier study focused on horizontal flows (Ibarra et al, 2018). TOWER consists of a liquid-liquid separator (total capacity of 450 L), two storage tanks (one per liquid phase, each with a maximum capacity of 680 L), two vertical pumps (each with a nominal capacity of 160 L/min) that deliver the liquid phases separately to the test section inlet, and an inclinable test section.…”

“…The oil phase was introduced from the top and the water from the bottom into this inlet section, which was also equipped with a series of flow conditioners for the purpose of promoting uniformity, reducing large-scale turbulent structures and secondary flows. Details of the inlet section can be found in Ibarra et al (2018).…”

“…The full set of investigated flow conditions covered in the present experiment campaign is given in Table 2 as a function of the mixture velocity, water cut, and in situ Reynolds number (at the optical measurement location) defined for phase i as Rei = ρiUiDhi/μi. This definition is based on the bulk in situ fluid velocity (see Table A1 in Appendix A) Ui = Qi/Ai where Ai is the crosssectional area occupied by the respective phase, and the hydraulic diameter Dhi of each fluid calculated from the liquid/pipe wetted perimeters, Si, based on the mean water layer height, ⟨hw⟩, and assuming a flat interface in the azimuthal direction from the expression Dhi = 4Ai/Si, thereby neglecting the error related to the curvature of the interface as it meets the wall at the contact-line, similar to (Ibarra et al, 2018). We note here that all our results are based on measurements in the vertical plane that passes through the centreline of the pipe (where the laser sheet is located), and that the interface height and the curvature of the interface outside of this plane, including where the interface contacts the pipe wall, cannot in general be inferred from these measurements.…”

“…In a recent study by the present authors (Ibarra et al, 2018), a novel simultaneous two-line (two-colour) technique combining planar laser-induced fluorescence with particle image/tracking velocimetry was implemented in horizontal stratified and stratified-wavy oil-water flows (non-RI-matched fluids). The present work is extended to low-inclination upward flows in order to provide detailed space-and time-resolved phase and velocity information at low water-cuts to The rest of this paper is organised as follows.…”

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

“…A smooth contraction with a honeycomb screen was placed after the pressure Tank II in the connection between the tank and the test section, to help straighten the flow by eliminating any secondary-flow history, while also reducing the inner pipe diameter (D) The raw images recorded were initially spatially calibrated and corrected for optical distortion through an algorithm of DaVis 7.2 (LaVision) software, which matches the camera's coordinates to the pattern of a graticule target [26][27][28] , shown in Fig. 2(a), where x and y are respectively the streamwise and spanwise spatial components.…”