Investigation on drag reduction phenomenon in oil-water dispersed pipe flow via wire-mesh sensor

Liquid-liquid flows are present in a wide range of industrial processes; however they have not been studied as intensively as gas-liquid flows. The interest in two-phase liquid-liquid flows have increased recently mainly due to the petroleum industry where oil and water are often produced and transported together for long distances. Nevertheless, the frictional pressure gradient in oil-water pipe flow not rare cannot be predicted by correlations developed for gas-liquid flow. The dispersed flow pattern is common in crude oil transmission pipelines and offshore pipelines, with either oil or water as the dominant phase. An interesting feature of dispersed flow is that it can behave as a non-Newtonian fluid. There are several works on drag reduction in single and gas-liquid two-phase flows, but only few on liquid-liquid flow. Drag reduction phenomenon in oil-water flows without the addition of any drag reduction agent has been detected in previous works, but the physics behind the phenomenon is yet not well understood. This work’s main goal is the experimental study of the drag reduction phenomenon in dispersed oil-water flow. Pressure gradients were measured during the flow of oil (860 kg/m³ density and 100 mPa.s viscosity) and water. The experimental work was performed in a 12-m-long 2.62-cm-i.d. horizontal glass pipe. A new wire-mesh sensor based on capacitance (permittivity) has been employed in this study. The sensor consists of two layers made of 8 steel wires each separated 1 mm from each other. It is able to discriminate fluids having different relative permittivity values in a multiphase flow and was used to measure local, transient and time-and-space averaged phase fraction distributions in the flow cross-section. A high-speed video camera and the Quick Closing Valves technique were used to compare and validate the signals of the wire-mesh sensor.