An experimental study of pulsatile mixing in a T-junction at low/ moderate Reynolds number

Mixing of a 180 degrees T-junction with digitally pulsating component-fluid branches has been experimentally studied. A range of Reynolds numbers (6.7 <= Re <= 427.8) and dimensionless pulsation frequencies (Strouhal numbers, 0.024 <= St <= 0.754) have been considered with a fixed 1:1 component-fluid ratio. The study identified two Reynolds-based regimes wherein mixing performance is primarily a function of the Strouhal number (Re less than or similar to 200) and mixing performance is primarily independent of Strouhal number (Re greater than or similar to 200). At low Reynolds number, the mixing method is primarily diffusive and, therefore, depends heavily on the component-fluid topology, which in turn is strongly dependent on St. Topological evolution from pulsatile-type (P-type) to non-pulsatile (N-type) results in an optimum Strouhal number for maximal mixing: St * approximate to 0.1. At elevated Reynolds number temporal instability develops, the dependency of the flowfield on St is broken, the primary mixing mechanism is no longer diffusive and a high degree of temporally averaged mixing results. Though temporal instability likewise develops in the non-pulsatile case for equivalent Reynolds numbers (based on the branch flow rate) and this effect cannot wholly be attributed to pulsation, but is rather primarily a Reynolds number effect.