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

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