Momentum and mass transport over a bubble mattress: the influence of interface geometry

In this study we investigate numerically how a partially slippery bubble mattress can be employed to enhance momentum and mass transport. The bubble mattress, which is a superhydrophobic surface, consists of an array of slippery gas bubbles with no-slip walls in between. We consider a pressure-driven laminar flow over the bubble mattress, with a solute being supplied from the gas bubbles. The results show that, because of effective wall slip, solute transport can be enhanced significantly with respect to a fully saturated no-slip wall. The enhancement depends on the interface geometry of the bubble mattress, i.e. on the bubble size, protrusion angle, and surface porosity. In addition, we demonstrate that the mass transfer enhancement disappears below a critical bubble size. The effective slip vanishes for very small bubbles, wherefore interfacial transport becomes diffusion dominated. For large bubbles, solute transport near the interface is convection enhanced. A bubble mattress can be utilised to enhance momentum and mass transport simultaneously, although the enhancement disappears for vanishing bubble size.