Influence of Slip-Yield Stress Model on Microscale Atomization Induced via Surface Acoustic Waves

This study theoretically examines how the slip yield stress boundary condition affects the interfacial dynamics of a millimeter-sized water drop positioned on a rigid substrate and subjected to destabilization through surface acoustic waves (SAWs). The substrate under consideration allows hydrodynamic slippage only when the shear stress exerted by the fluid drop on the surface reaches a critical (yield) value. We solve the governing equations of drop hydrodynamics using lubrication theory. This leads to an evolution equation that describes interfacial destabilization in terms of the acoustic capillary number, critical shear stress, and slip length. The interfacial dynamics derived from the numerical solution of the evolution equation led us to identify the slip-yield stress model as a novel and valuable passive aerosol regulation mechanism at SAW atomization, with the capability of providing drop aspect ratios and aerosol sizes located amidst the no-slip (infinite critical stress) and Navier-slip (zero critical stress) cases; our results also show that, as the critical stress rises, there is increasing mitigation of slippage influence over SAW atomization, which, in turn, leads to the development of aerosol diameters up to one order of magnitude larger than those provided by the classical Navier-slip condition. Furthermore, we explore the relevance of the slip-yield stress model concerning a fundamental aspect of SAW atomization: the decrease in interfacial energy. Our results demonstrate that the slip-yield stress condition reduces energy consumption compared to the no-slip condition.