Refractive index matching and marking methods for highly concentrated solid–liquid flows

Abstract Two index-matched systems of solid particles in liquid have been developed to enable the study of velocity and concentration distributions in the highly concentrated solid–liquid flows. The mixtures have excellent optical transparency up to depths exceeding 80 mm at concentrations up to 50% solids by volume. Highly visible marker particles with nearly the same mechanical properties as the index-matched particles are formed by metal plating or substitution. Good quality images of marker particles are obtained in both stationary and moving two-phase mixtures, and permit accurate tracking of the individual markers.