Drop impact onto attached metallic meshes: liquid penetration and spreading

The interaction between drops and porous matter has important applications in many fields such as painting, paper coating, design of textiles, filtration and therapeutic delivery, the latter can include also reconstructive surgery processes. Since the phenomenon of droplet impact onto a porous surface is particularly complex, a first step consists in analysing impacts on 2D structures, such as metallic porous layers. The present paper shows the case of drop impacts onto metallic meshes attached to a solid substrate. The pores are squared and not planar, due to the woven structure of the meshes: the dynamics of the flow is particulary complex, but it resembles more realistic cases. In analysing the impact of droplets of water, acetone and a mixture of glycerol and water on meshes with different pore sizes, three main outcomes were observed for both test cases: deposition, partial imbibition and penetration. Higher velocity impacts lead to droplet splashing followed by deposition, partial imbibition and penetration. A higher amount of liquid penetration is linked to a higher velocity impact, lower viscosity and a larger dimension of the pore size. A map of the regimes is proposed introducing two dimensionless numbers M and γ, that are functions of the Weber and Reynolds numbers and pore and wire sizes. Previous papers have not considered the role of the wire diameter. The two numbers allow a clear separation of the outcomes and a practical use of the results.