Direct numerical simulations of laminar droplet breakup in static mixers under different inlet conditions

The effect of different inlet dispersed phase morphologies on the mechanics underlying droplet deformation and breakage across a standard SMX static mixer is studied. Three conditions are considered whereby the dispersed phase fraction is simultaneously varied to account for the influence of coalescence events: 1) negligible coalescence, three individual droplets mimicking a controlled syringe injection; 2) low dispersed phase fraction, numerous variable-sized droplets simulating a pre-mixed inlet; and 3) intermediate dispersed phase fraction, jet inlet emulating a standard phase injection from a gear pump. This study implements massively-parallel high-fidelity three-dimensional direct numerical simulations with a hybrid front-tracking level-set interface capturing algorithm. Governing forces and prevaling deformation/breakup mechanisms are identified for each inlet condition based on literature models. Some of these include 3D elongation and rupture at cross-points driven by buoyancy forces, or droplet adherence to an interstice, growth, and posterior detachment as smaller drops driven mostly by viscous and frictional forces. These mechanisms are elucidated by the strain rate and maximum stretching efficiency profiles across the mixer.