Investigation of immersion media and materials for optical diagnostics in curved wall channels by the matching index of refraction

\nFive different refractive liquids and two possible transparent solid materials were tested to perform matched index of refraction (MIR) optical flow measurements and visualisation in channels with curved walls, for example, models of rods in fuel assemblies. The results of the tests showed that the selection of refractive liquid is always a compromise between effective and sometimes hazardous substances such as p-Cymene or essential oils and their less harmful substitutes with higher dynamic viscosity, such as white mineral oil.\n