Experimental study of liquid drop impact onto a powder surface

The initial dynamics of liquid drop impact onto powder surfaces is studied experimentally using high-speed photography. For a range of bed packing fractions, ϕ, liquid physical properties and impact velocities, ui, we observe a variety of phenomena that can be representative of a hydrophobic surface, a rough surface or a porous medium. The solids packing fraction in the bed, 0.38 ≤ ϕ ≤ 0.65, and the impact Weber number, 3.5 ≤ We = ρDui2/σ ≤ 750, (where ρ, D and σ are the drop density, diameter and surface tension respectively) are shown to be the critical parameters governing the outcome of an impact. For high packing fractions, ϕ ≳ 0.5, we show that the observed spreading, rebound and splashing can be broadly characterised in terms of the Weber number while for looser packing fractions, ϕ ≲ 0.5, we observe powder ejectas and provide a qualitative description of the granule nucleation at the centre of the impact sites.

In this study, we examined the dynamics of liquid drop impact onto powder surfaces in order to quantify the different regimes such as spreading and splashing. We also study the influence of the impact velocity and liquid physical properties upon the generation of satellite drops and nucleation. Some interesting observations such as ‘pinning’ due to the heterogeneous void structure were also made.Figure optionsDownload as PowerPoint slide