Micro-patterned surfaces obtained by magneto-electrodeposition for heat transfer enhancement – SURFMET

The objective of SURFMET is to optimize the functionalization of metal alloy surfaces by micropatterns obtained by magneto-electrodeposition in order to improve heat transfer while maintaining a good durability under shear and corrosion in aqueous media.
More specifically, we are interested in the use of patterned deposits to ultimately control nucleated boiling regimes in elongated sub-millimeter channels of very large aspect ratio. The patterns developed will be deposited on copper-silver alloys prepared by helium cold spray method. These alloys with high mechanical and electrical performances are now currently used at LNCMI as base materials for the fabrication of coils for production of intense magnetic fields. These coils can be considered as archetypal compact heat exchangers subjected to extreme cooling flows (up to 10 MW.m-2).
In this project we will use electric and magnetic fields for:
- developing specific textured surfaces (such as multi-scale hybrid structures) under high magnetic fields by exploring the evolutionary and unique character of the deposition process.?
- performing wetting experiments at drop or bubble scales under uniform/non-uniform magnetic/electric fields.
- quantifying the reliability of these deposits under critical phase change conditions (nucleate boiling regime), as these deposits can ultimately be deposited on the active parts of the coils used for high field generation in LNCMI.
Magneto-electrodeposition offers new multi-scale hybrid solutions by allowing the growth of the crystal branches to be continuously influenced without modifying the crystal habitus, and without organic additives. The use of intense or non-uniform magnetic fields makes it possible to envisage the implementation of a new process combining macro-structuring and microporosity in the same step. This would make it possible to find an optimum of heat transfer enhancement, more particularly by controlling the nucleation sites, by exploring the monitoring and monotopic character of the deposition process.
The fundamental description of magneto-deposition (nucleation/growth mechanisms, process-structure-property relations studied by a multi-scale and interdisciplinary approach) will be particularly studied by considering electro- and magneto-hydrodynamic flows. A final criterion for the choice of micro-patterns with respect to the change in heat transfers will be based on different system models dedicated to electro- and magneto-wetting in nucleate boiling conditions.
The choice of an electrochemical method for the realization of structured functional deposits allows the users in the long term to serenely envisage scaling up for many industrial applications. In this project we will carry out a proof of feasibility for the possibility of scaling up magneto-electrochemical processes. Thus, we will carry out deposits, whose processes will have been optimized in the first part of the project, on the walls of electromagnet windings for the production of intense magnetic fields. The project draws on the complementary skills of three laboratories in the fields of electrochemistry under magnetic fields, microfluidics, electromagnetohydrodynamics, surface physicochemistry, heat transfers and magnetic field production. This project will benefit from the experience gained from previous collaborations between the proposed partners. These collaborations all involved high-field experiments carried out at the LNCMI in the fields of magnetoelectrochemistry and magnetohydrodynamics.