Diagnostic Technique for Quantitative Resolution of Three-Dimensional Liquid-Gas Phase Boundaries in Microchannel Flows

The morphology of liquid-gas interfaces in adiabatic two-phase microchannel flow through a transparent acrylic microchannel of 500 μm × 500 μm square cross section is investigated. Water seeded with 0.5 μm-diameter fluorescent polystyrene particles is pumped through the channel, and the desired adiabatic two-phase flow regime is achieved through controlled air injection. The diagnostic technique relies on obtaining particle position data through epifluorescent imaging of the flow at excitation and emission wavelengths of 532 and 620 nm, respectively. The particle positions are then used to resolve interface locations to within ±2 μm in the viewing plane. This technique was previously demonstrated by the authors for a static meniscus in a capillary tube. The complete interface geometry between liquid and gas phases is obtained for operation in the annular flow regime by mapping the interface within individual focal planes at various depths within the channel. The diagnostic technique is shown to successfully locate and measure interfaces between transparent, immiscible fluids in a dynamic microchannel flow environment.