A laminar lid-driven cavity flow was constructed to represent the fundamental characteristics of an industrial dynamic mixer. The flow patterns and mixing process in the cavity were measured by using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) experiments respectively. The refractive indices of the two miscible liquids involved were carefully matched to allow for unhindered optical access. The mixing process was predicted by using computational fluid dynamics (CFD) including models for species transport. The simulated flow and mixing results are in good agreement with the experimental data. The effects of density difference and viscosity of the two miscible fluids on the mixing process were evaluated. Minor variations in the densities of the fluids have significant influence on the mixing process in terms of the coefficient of variation as a function of time. The dimensionless group Ar/Re (Archimedes number over Reynolds number) is proposed to characterize the mixing process in the cavity.