4-D Particle Tracking Velocimetry Applied to Gas-Liquid Reactors

In the chemical industry, many process operations depend on complex multi-phase flow processes. Apart from the transport of fluids through pipelines or vessels, flow processes in combination with chemical reactions, heat and mass transfer are of crucial importance. Detailed knowledge of the local parameters becomes more and more important with increased development levels of process operation. In this context we present a novel technique that allows us to follow optically visualized seed particles or air bubbles through space and time (4-D) in a liquid container, e.g. in a gas-liquid reactor. The method combines the well known strengths of 3-D PTV with stereo calibration and correlation techniques to obtain 3-D Lagrangian velocity fields. Using a sub-pixel accurate calibration procedure, a high spatial resolution can be achieved. Compared to LDA or ultrasound methods, 4-D PTV allows spatially high resolved measurements of flows in the whole measuring volume. The experimental setup works with two standard CCD video cameras looking into the gas-liquid reactor. The air bubbles are visualized by light refracted at their surface from a light source facing the CCD cameras. PTV is ideal for dilute two-phase systems because it provides local information on both bubble and liquid velocity. Furthermore, in combination with bubble size measurements, it allows determination of the local gas capacity. Currently the system is used for basic research on flow processes in bubble columns. The experimental findings are used to verify of models used in numerical simulations of the flow processes (CFD). Of particular interest is the evaluation of significant terms in the system of equations for the Euler/Euler model.