Simultaneous measurements of liquid velocity and tracer concentration in a continuous flow stirred tank

This work concerns the simultaneous measurements of the velocity of a liquid and of the concentration of a passive scalar in a standard geometry stirred tank provided with a continuous feed stream. The data are collected close to the tracer inlet on a vertical plane portion located in the vessel top region by a combined Particle Image Velocimetry and Planar Laser Induced Fluorescence system. The mean and fluctuating velocity and concentration components in the axial and radial directions obtained under stirred and unstirred conditions are presented. Following the definitions provided in the realm of the gradient diffusion hypothesis for the turbulent scalar transport, the measured variables are further exploited for the calculation of the turbulent viscosity, the turbulent diffusivity and their ratio, that is the turbulent Schmidt number. For the investigated conditions, the turbulent Schmidt number values are in the range 0.7–1.0, although significant local variations are observed.