Droplet Growth by Coalescence in Binary Fluid Mixtures

The evolution of the drop-size distribution in immiscible fluid mixtures following well-specified shear histories is investigated by in situ microscopy, allowing determination of the shear-induced coalescence efficiency $\varepsilon$. At small capillary number Ca, $\varepsilon$ is constant, whereas at larger values of Ca, $\varepsilon$ decreases, in agreement with theory accounting for slight deformation of the drops in close approach. Coalescence causes the drop-size distribution to broaden in general, but greater deformation of the larger drops at high shear rates causes the drop-size distribution to remain narrow.