Post-doctoral position on the influence of surface conditions for spray impact, LEGI, Grenoble

 Context: Liquid sprays impacting a surface are commonly involved in processes such as cleaning, cooling, coating, and medical or agricultural spraying. In this geometry, there are two distinct zones: the zone under the spray and the film spreading radially beyond the impact zone. The fluid mechanics of such a film is complex because it is fed by a turbulent two-phase flow, bordered by a possibly structured solid surface, and subjected to an intense shearing gas flow. This makes spray impact an inherently coupled multi-scale problem. A large number of studies have sought to give a comprehensive understanding of impinging spray in the context of spray cooling or coating. Nevertheless, several questions still remain to be tackled in spray cleaning. First, a specificity of this process is that the spray formation involves a high-speed gas jet, whose influence on the impact pattern has only received little discussion in the literature. Second, although spray impact is a highly energetic process in which the kinetic energy of the drops largely exceeds the adhesion energy of the small particles by several orders of magnitude, a much lower cleaning efficiency is observed on hydrophobic surfaces than on hydrophilic surfaces. This suggests subtle redeposition phenomena of the particles in the area beyond the film, which have never been studied.

Position: The candidate will undertake a multiscale study of the structure and stability of the highly sheared parietal liquid film formed around the impact zone of a spray on a surface. The stability of the film outside the impact zone will be characterized as a function of the nature of the surfaces, whether hydrophilic, hydrophobic, or structured, and the intensity of the co-current gas flow using ultra-fast and resolved multi-scale imaging techniques developed at LEGI. The preparation and characterization of the surfaces using physico-chemistry techniques will be done at LIPhy, and attempts at wetting controlled using complex surface structuration will be considered in a second part of the project. Finally, modeling and applications of the results for spray cleaning applications are also part of the project’s outcome.