ANALYSIS OF THE RAINBOW SCATTERING BY HOMOGENEOUS AND INHOMOGENEOUS DROPLETS IN LIQUID-LIQUID SYSTEMS

International audienceThis communication deals with the optical characterization of droplets and fluids parameters that are relevant for liquid-liquid extraction processes, and notably, for nuclear fuel reprocessing. In immiscible liquid-liquid dispersions, i.e. droplets with a homogeneous but low value relative refractive index, the first order rainbow is localized in the near forward to sideways region. It exhibits also an unusual higher contrast for a parallel polarization illumination. Nevertheless, it is possible, considering appropriate light scattering models and inverse methods, to derive from its analysis the droplets' size and composition. When a mass transfer occurs, the refractive index of the droplets and the surrounding fluid become inhomogeneous. In a pure molecular diffusion regime, the rainbow patterns can still be interpreted as well, allowing the estimation of relevant properties for chemical engineering processes, like molecular diffusivities or the distribution constant. 1 Immiscible systems-homogeneous droplets We first consider that the extraction process is already completed or has not yet started [1]. The composition of the single or cloud of droplets is thus homogeneous. For obvious safety reasons, simulant and mixing fluids (TPH and Marcol) were used in this study in place of the real fluids involved in nuclear fuel reprocessing. TPH is the diluent employed in the actual process, while Marcol is a saturated hydrocarbon liquid with a higher refractive index than TPH but with comparable viscosity and surface tension. In the same way, for the continuous phase, demineralized water (HPLC-grade) replaces the nitric aqueous solution used in the process