TraThI

In the energy technologies of the future, the thermal power densities to be transferred will be greater than 1000 W.cm-2. Current techniques do not allow the extraction of such high power densities. To meet these challenges, new concepts must be implemented. In this context, thanks to a multi-scale approach, the TraThI project aims at a better understanding of the transfer mechanisms at the interfaces in order to propose new heat extraction techniques, able to reach such thermal power density levels.The approaches will be experimental, numerical and theoretical, bringing together partners with complementary skills (thermal, two-phase flow, surface treatment, micro-fabrication, micro-sensors). The experiment we propose consists in studying the heat transfer at the transition from convection to nucleate boiling regime. The fluid motions generated at the onset of bubble nucleation, over micrometer thicknesses, promote heat exchange. Experimentally, the resolution of thermal and fluidic measurements at the micrometer scale, coupled with the controlled structuring of nucleation surfaces at the sub-micrometer scale, will allow studying the fluid motion in the immediate vicinity of the wall from the scales of bubble nucleation to those of bubble detachment and measuring the associated heat transfers. Two canonical experiments will allow to establish a unique data bank that will serve as a reference for numerical and theoretical approaches. The numerical approaches will help to properly identify the near-wall temperature fields at the triggering limit of bubble nucleation. The theoretical approach, based on the heat flux partition model, will rely on the data bank established in this project to propose heat transfer laws. The results of this work will allow us to evaluate the potential of the heat transfer enhancement for future energy technologies where heat flux densities are not possible with current techniques.