A NOVEL INDIVIDUAL WAVE VISUALIZATION AND TRACKING TECHNIQUE IN ANNULAR FLOWS BASED ON AN ADAPTATION OF THE TOTAL INTERNAL REFLECTION METHOD USING A LASER LINE

Annular flow is a common multiphase flow in industry, thanks to its excellent heat transfer characteristics given by its thin, wavy film. Due to its complexity, high resolution wave experimental data are fundamental for validation of increasingly complex CFD annular flow simulations, often requiring elaborate experimental setups. Therefore, we present a novel and simple technique allowing for wave visualization and tracking in annular flows: Line-Total Internal Reflection Method (L-TIRM). L-TIRM also enables wave velocity distributions measurements, allowing deep insights into the flow dynamics. L-TIRM is an adaptation of the total internal reflection method (TIRM) using a laser line instead of a laser point. Our innovative implementation transforms a local measurement technique into a flow imaging technique able to visualize the topology of thin films along a straight line, similarly to methods such as PLIF (planar laser induced fluorescence), but without need for a fluorescent dye. The technique only needs a camera and a laser and is fully non-intrusive. We experimentally characterize L-TIRM range of applicability in upward adiabatic annular flows and verify L-TIRM measuring capabilities using optical ray tracing simulations which explain L-TIRM measurement physics. Results are then validated against the literature and the already established conductivity film sensor technology in a setup allowing simultaneous wave velocity measurement. Moreover, additional experiments compare L-TIRM to classic TIRM, highlighting that the former is more informative when it comes to wave analysis. However, while L-TIRM still retains some film thickness information, the measurement of this property is less robust than classic TIRM.