LEIDENFORCE (2025-2028) Finance: Horizon Europe (MSCA-Doctoral Network) Site web Collaboration : Alexis Duchesne (CNRS-ULille), Benjamin Sobac (UPPA), Anne-Laure Biance (CNRS-UCBC), Scott Waitukaitis (ISTA), David Quéré (CNRS-ESPCI), Detlef Lohse (UTwente), Maria Fernandino (NTNU), Benoit Scheid (ULB), Pierre Colinet (ULB) When a liquid droplet is placed on a solid surface with a temperature significantly higher than the boiling the surface on a thin layer of its own vapor, a phenomenon known as the Leidenfrost effect. While this effect is highly undesirable in certain cooling applications due to the reduced energy transfer between the solid and evaporating liquid caused by the poor heat conductivity of the vapor, it can be of significant interest in various processes where avoiding contact with the surface is advantageous. The LeidenForce project aims to comprehensively study the Leidenfrost effect and propose novel applications, either to mitigate its adverse effects or leverage its advantages. LeidenForce intends to (i) shift the fundamental understanding of the transition to the Leidenfrost state, (ii) optimize the heat transfer between the droplet and the substrate, (iii) utilize the isolated droplet to manipulate small amounts of liquid in unconventional scenarios (e.g., on a liquid surface, within a channel), and (iv) harness the vapor film to capture or confine particles using an external electrical field. The practical implications will be leveraged by non-academic institutions involved in aviation (such as AIRBUS), metallurgy (CRM), cryogenics (Air Liquide), and space exploration (Centre Spatial de Liège). In aviation, managing cryogenic fuel is a crucial step toward achieving zero-emission flights. In metallurgy, innovative cooling methods will be developed based on mitigating the Leidenfrost effect. Air Liquide will address cooling issues by introducing particles into the evaporating liquid to modify the Leidenfrost effect. Lastly, at the Centre Spatial de Liège, Leidenfrost droplets will be utilised to delicately clean surfaces by trapping particles within these contactless droplets. RESEC (2024-2026) Finance: CNRS-WBI Collaboration : Alexis Duchesne (CNRS-ULille) On entend par surface extrêmement chaude, une surface dont la température est bien au-delà de la température d’ébullition du liquide refroidisseur. Dans ce régime, un fin film de vapeur (et donc un excellent isolant thermique) apparait entre la surface chaude et le liquide refroidissant. Il en résulte une diminution drastique (un facteur 100) des échanges de chaleurs entre la surface et le liquide. Cette situation, catastrophiques lors de la surchauffe d’un réacteur nucléaire, est également problématique dans le domaine de la métallurgie et, de manière générale, dans toutes les situations de refroidissement. Pour contrer cet effet, notre stratégie consiste à étudier l’effet de particules solides embarquées dans la goutte ou dans le jet de manière à percer le film de vapeur qui isole le liquide de la surface chaude. Deux cas seront étudiés: l’eau et l’azote liquide. Il convient de déterminer à quel point les résultats sont transposables du domaine `métallurgique’ au domaine `cryogénique’. STABAB: Stability of Antibublles (2023-2026) Finance: PDR (FNRS) Collaboration : Benoit Scheid (ULB) An antibubble is a drop inside a bubble in a liquid. Bubbles and droplets are well-established elementary components in microfluidics, but this project aims at suggesting the antibubble as the new elementary component in microfluidics, combining the assets of both bubbles and droplets. The use of antibubble should ultimately lead to technological breakthroughs such as allowing for unique liquid/gas transfer capabilities and all-aqueous emulsification at high throughput, as targeted in drug micro-encapsulation. However, one of the main limitations of using antibubbles for practical purposes is that it is an ephemeral object, challenging the success of using antibubbles for some applications like in drug release. One must therefore address the crucial point of antibubble stability, the goal of the present research being to investigate several strategies for stabilizing antibubbles. The strategies consist in counteracting against the natural drainage of the gas shell or, in other words, against the thinning of the bottom of the gas shell. To reach this goal, four means are envisaged: (i) Mechanical by tailoring flows around the antibubble or by using particles at the interfaces, (ii) Thermal by inducing the vaporization of one of the liquids in presence to feed the gas shell, (iii) Chemical by allowing exchange of matter between the liquid inside and outside the antibubble through the gas shell under the action of a concentration contrast between the liquids (in glycerol or in salt), and (iv) by simply suppressing the gravity in parabolic flight campaigns. These strategies are considered on the macro scale (cm) and on the micro scale (100 μm) to obtain a coherent and detail model for the stabilization of the antibubbles. WOLFLOW: Wrapping Objects with Liquid Flows by Lifting them Out of their Wakes 2017-2021) Finance: PDR (FNRS) Collaboration : Benoit Scheid (ULB), Vincent Terrapon (ULiège) When an object is lifted out of a pool of fluid, the object entrains a certain quantity of fluid that eventually drains down. This project aims at exploring and rationalising experiments concerning these micro-flows of fluid, i.e. flows dominated by viscous shear along any arbitrary objects. The crossing of a fluid interface by an object remains a stimulating field of research and is of primary importance in numerous industrial processes such as in galvanisation, painting, and more generally in coating processes. Two main questions have still to be addressed: (Q1) Can we predict the quantity of fluid that is embarked by the object? (Q2) How fast and homogeneous the liquid drains out? The experiments will be conducted at ULg-GRASP and will consist in pulling (in a control way: speed, force) canonical objects (like a sphere, a cylinder...) out of a pool of fluid. The quantity of entrained liquid, the drainage dynamics will be measured. The influence of the fluid, especially the presence of surfactant molecules, will be investigated. The experiments will be rationalised using two complementary approaches. Numerical simulations will be performed at ULg-MTFC. The fluid-structure interaction will be modelled using an original code. The complexity will be increased starting from a 2D cylinder model. Moreover, at ULB-TIPs, a model will be constructed in the frame of the lubrication theory and implemented into Comsol for time-dependent simulations. The Arbitrary- Lagrangian-Eulerian (ALE) method will be used for moving solid boundaries. The conjonction of the experimental results, the numerical simulation and the drainage model will allow to obtain an unified description of the coating of an arbitrary object pulled out of a liquid bath.

Kick-off meeting is the most expected meeting. It will take place in the center of the field in Brussels. This will allow a on-site discussion to settle and implement our plan.