Effect of Chamber Depth Modifications on Flow Regimes and Mixing Performance in Cross-Shaped Mixers

Abstract

Flow and mixing in cross-shaped mixers with various chamber depths (w i /h, in which w i and h are the chamber depth and inlet height, respectively) were studied by Plane Laser-Induced Fluorescence (PLIF) and numerical simulation at 20 ≤ Re ≤ 500. Emphasis was placed on engulfment flows and pulsation flows, as well as the dominant role of vortices and their dynamic evolution. For w i /h > 0.3, segregated flows, steady engulfment flows, pulsation flows, and unsteady engulfment flows emerge successively with increasing Reynolds number (Re = ρu 0 D h/μ, where ρ, μ, D h, and u 0 are the fluid density, fluid viscosity, inlet hydraulic diameter, and inlet bulk mean velocity, respectively). As w i /h decreases, engulfment and pulsation flows are delayed, and the recirculation regions induced by vortex breakdown are shifted. For w i /h ≤ 0.3, pulsation flows and recirculation regions disappear, and a hybrid mode of deflecting oscillation and vortex merging is identified. The degree of mixing was quantitatively analyzed to reveal the mixing mechanism. At low Re, an increase in w i /h improves the mixing due to the earlier onset of steady engulfment flows. For higher Re, better mixing appears for w i /h ≤ 0.3 attributed to vortex merging and deflecting oscillations.