Magnetowetting at drop scale (Magnéto-mouillage à l’échelle d’une goutte)

This fully founded PhD thesis is proposed in the framework of a project supported by the Agence Nationale de la Recherche (ANR): the SURFMET project. The SURFMET project proposes new technological routes to promote heat transfer enhancement. Among the different work packages in the SURFMET project, one consists in investigating how electro- and magneto-wetting affects nucleate boiling. Among challenges, there is the will to better predict the arising of critical regimes in systems which host electric and magnetic fields, such as the large magnets of LNCMI. In case of nucleate boiling, nothing is known on the influence of electro-wetting or magneto-wetting on the nucleation and growth dynamics of vapor bubbles inside a millimetric gap. As a first step, the research proposed will focus on magneto-wetting experiments. Most of them have been conducted so far on ferrofluids. In this project, the intern will conduct experiments (and shape calculations) on diamagnetic water drops using either NdFeB permanent magnets (1T) or a large magnet (10-20T) available at LNCMI (Grenoble CNRS). Magneto-wetting properties under uniform (and later non-uniform) magnetic field conditions will be characterized. The experiments will be first carried out under as uniform as possible conditions to eliminate contributions of B-gradients (magnetophoretic forces). An exceptionally good uniformity of the magnetic field is expected from the inner of the large high field magnets at LNCMI. A first set of experiments will be carried out on sessile drops deposited on a neutral substrate either made of copper (wetting case) or made of Teflon (non-wetting case). Due to the magnetic permeability jump at the drop surface, the shape of the sessile drop is expected to be modified. The shape change will be measured from a camera and a light absorption imaging method. The shape change is a good means to validate the Laplace-Young equation to be revisited. From the experiments, the dependence of the contact angle on the magnetic actuation is expected to be obtained. Depending on the observations, complementary experiments on bubble wetting will be developed to extend the investigation up to phase change.

Funding category: Autre financement public
ANR
PHD title: Mécanique des fluides, Energétique, Procédés
PHD Country: France