In this work, a novel two-line laser-based diagnostic measurement technique was developed and applied to obtain combined space- and time-resolved phase and velocity information in low-inclination upward (<+5°) stratified flows of oil (Exxsol D140) and water. The strength of this technique is in enabling direct measurements in the nonrefractive-index-matched fluids of interest, as opposed to substitute (optically matched) fluids whose properties may be less representative of those in real field-applications. The experimental test-section consisted of a 32-mm internal diameter pipe with a total length of 8.5 m. Results reveal interesting interactions between the co-flowing liquid phases. The velocity gradients at the interface are enhanced at high pipe inclinations for upward flows as the oil and water velocities increase and decrease, respectively. This also has a direct effect on the velocity fluctuations (quantified through their rms) and on the interfacial instabilities, which in turn affect the local velocity distributions in both phases.
The flow of oil and water in pipes is encountered in a wide variety of industrial applications, especially in transportation pipelines which can extend for long distances at low pipe-inclinations (<±5°). The distribution of the phases (flow regimes) along the pipe depends on a number of considerations, namely, fluid properties, flow velocities, and pipe characteristics. Moreover, the design of the inlet section where both phases are introduced into the main pipe-section can affect the behaviour of the flow when studying oil-water mixtures in a laboratory environment (i.e., at relatively short lengths from the inlet) . Flow regimes are commonly classified into two main categories: separated and mixed flows. The former are characterised by two continuous layers at the bottom and top region of the pipe in which the interface can be smooth of wavy. Mixed flows are identified by the existence of droplets of one or both phases into the other, for example, dual continuous flows, dispersion of water-in-oil and dispersion of oil-in-water.