AbstractThe interaction between drops and porous matter has important applications in many fields such as painting, paper coating, filtration and biology, the latter considering for example reconstructive surgery processes, when blood impregnation of scaffolds is a very critical issue. Since the phenomenon of drop spreading onto a porous surface is particularly complex, a first step in developing our understanding of the underlying physics consists in analysing impacts on 2D deterministic structures, such as metallic meshes. The experiments are reproduced using three different liquids: water, acetone and a solution of water and glycerol. The meshes pore dimension and wire diameter have a range of respectively 25-400 μm and 25-220 μm. A combination of different surface porosities and liquids physical properties is needed to study how the impact outcome is influenced.
The present work shows the cases of drop impacts onto meshes attached to a solid substrate and of drop impacts onto the same meshes but suspended without a substrate.
Three main outcomes were observed for both cases: deposition, partial imbibition and penetration. The penetration into suspended meshes leads to a spectacular multiple jetting below the mesh.
In the first configuration of the attached meshes, the squared meshes were bonded to a flat, solid plate made of stainless steel in order to reduce the effect given by air entrapment. For the suspended meshes, even if the vertical micro-movements of the mesh are reduced as much as possible using heavy steel rings, the effect of the layer displacement may influence the impact outcome. Hence, in order to evaluate such effect, different ring diameters are considered which offered smaller and larger unclamped area for the suspended mesh compared to the original case.
A higher amount of liquid penetration is linked to a higher velocity impact νi, lower viscosity and a larger dimension of the pore size. An estimation of the liquid penetration is given in order to evaluate the impregnation properties of the meshes. For the case of attached meshes a map of the regimes is proposed introducing two dimensionless numbers.
|Date of Award
|Marco Marengo (Supervisor), Cyril Crua (Supervisor) & Dipak Sarker (Supervisor)