Coalescence dynamics of nanofluid droplets in an expansion chamber structure microchannel

Nanofluid droplets have considerable applications in industry. In this study, the coalescence dynamics of nanofluid droplets in an expansion chamber structure microchannel were visually investigated; the shape and liquid bridge evolutions of droplets were studied systematically. Five droplet coalescence flow patterns were observed: non-contact, double coalescence, cascade coalescence, compact slug flow, and jetting flow regimes. Due to the adsorption of nanoparticles on the fluid interface, a solidified layer is formed, which restrains the curvature change of the liquid bridge, slowing down the shrinkage of the liquid bridge. The evolution of the liquid bridge neck width with time could be divided into two stages: the dispersed phase control stage and the continuous phase control stage. The nanoparticles could affect markedly the dispersed phase control stage, while having less effect on the continuous control stage.