Development of a particle tracking-based measurement technique to map three-dimensional interfaces between transparent, immiscible fluids

Experiments were conducted to develop a microscale spatial measurement technique applicable to transparent fluid flows, with the target application being the determination of liquid geometries in multiphase flows. Air/isopropanol interfaces were used to simulate multiphase boundaries and were studied by examining menisci in capillary tubes. Fluorescent seeding particles of 0.5 μm diameter were added to the isopropanol working fluid. The use of fluorescent particles circumvented many of the noise-related issues characteristic of transparent and reflective systems. By exploiting the difference in the length scale between particle size, inter-particle spacing, and target feature size, the particle position data could be used to resolve spatial measurements within the sample, primarily the location of the interface within the field of view. Additionally, by adjusting the position of the focal plane within the sample, a three-dimensional map of the air/liquid interface was obtained.