Experimental and numerical investigation of a free rising droplet

A toluene droplet rising in a continuous aqueous phase is studied both experimentally and numerically. The experiments have been performed in a small scale, high-speed measuring unit with a high magnification device to image the process in all details. Numerical simulations are performed with the aid of the level set method implemented in the commercial CFD tool COMSOL Multiphysics 3.3a by COMSOL AB. A new technique for quantitative comparison of experimental and numerical results with respect to the droplet shape is presented. Both terminal velocity and droplet shape in experiments and simulations are found to be in excellent agreement. Based on the experimental and numerical data obtained, an improvement of an existing terminal velocity correlation is suggested. The adjusted correlation can be used for the design and optimisation of liquid–liquid extraction units.

► An experimental study of a toluene droplet rising in a continuous aqueous phase.
► A detailed numerical study of the same phenomenon with the level set method.
► A new technique for quantitative droplet shape comparison.
► An improved correlation for the droplet terminal velocity.