Measurements of interfacial film thickness for immiscible liquid–liquid slug/droplet flows

Abstract

A novel method for measuring the interfacial liquid film thickness between immiscible liquids of a slug/droplet in a micropipe is proposed. This method is capable of measuring an oil slug/droplet in water with the relative refractive index (m) between the immiscible liquids very close to one in a capillary tube. Unlike the measurement configuration for an air slug in water, an optical oriental for optimizing the refracted fringes pattern by the liquid–liquid interface is introduced. Measurements of film thicknesses of a kerosene oil droplet/slug in a water wetted capillary tube (m > 1) and a water droplet/slug in a kerosene oil wetted capillary tube (m < 1) were demonstrated. This diagnostic method is easy to implement and it will have great potential for immiscible liquid flow research in microfluidic channels.