Relation between oil-water interfacial flow structure and their separation in the oil-water mixture flow in a curved channel: An experimental study

Abstract

We investigate the oil-water separation in a curved channel under a range of inflow conditions, focusing on the fundamental multiphase flow physics occurring at the oil-water interface. With a silicone oil (viscosity: 10 mm2/s, density: 935 kg/m3), we perform a series of water-tunnel experiments to measure the evolution of oil-water mixture flow inside a curved channel, devised for realizing a continuous and effective oil recovery (separation). The oil-water mixture velocity at the channel inlet is 1.35–2.35 m/s (Reynolds and Froude numbers based on the inlet height and length of the channel are 0.6–2.0 × 104 and 0.14, respectively), and we vary the inlet oil volume fraction as 0.49–0.85. We find that the efficiency of oil separation is strongly affected by the oil-water interfacial flow structures and identify two typical flow patterns: wavy oil-water interface and dispersed-oil flow. When the inlet oil fraction is high ( > 0.74), the instability occurring at the wavy oil-water interface plays a dominant role in determining the oil recovery rate (which is as high as 80% in general). As the inlet oil fraction becomes smaller ( < 0.7), on the other hand, the oil dispersion starts to appear vigorously, which interferes with the oil separation process and the recovery rate drops below 60% at the oil fraction smaller than 0.5. Through the quantitative analysis of the optically measured oil-water interface phenomena, we suggest theoretical models to predict the oil recovery rate as a function of the interfacial fluctuation of wavy oil-water interface and the fraction of dispersed oil phase, depending on the inlet flow conditions. We also propose a strategy to maximize the oil recovery rate of large-scale oil-water separation device, which is expected to be beneficial in many applications.