Entanglement between thermodynamics and interfacial instabilities in binary fluids close to the critical point

• Applicant: Dr.-Ing. Holger Marschall
• Subject Area: Fluid Mechanics ; Chemical and Thermal Process Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 568906955

The objectives and the challenges of the present joint French-German project are to describe and understand the influence of interfacial tension effects on low Reynolds fluid flows, when it becomes extremely weak down to effective at the limit of miscibility. Interfacial instabilities, with their onset and their tension-dependent dynamics, thus represent a very appealing way to tackle these interfacial tension effects. Moreover, in order to raise a universal point of view, this project will propose investigating three complementary instabilities in near-critical liquid-liquid mixtures for which the interfacial tension vanishes at the critical point: Dripping & Rayleigh-Plateau (liquid jet & column), Kelvin-Helmholtz (driven by tangential stress of interfaces, and not by surface tension), and Bénard-Marangoni (coupling buoyancy / surface tension force in the presence of a thermal gradient). This choice offers a vision of interfacial tension effects on very different instability mechanisms. We will focus on their evolution when varying the shift in temperature to the critical point and eventually crossing it. The project is thus scientifically significant and relevant as it tackles the still unsolved problem of the entanglement between thermodynamics and fluidics in a universal framework, questioning laws and stability diagrams under out-of-equilibrium fluid conditions. The priority is thus of fundamental nature but the understanding of the dynamics at low tension and effective interfacial tension is relevant for applications like solvent extraction, enhanced oil recovery or intravenous drug delivery to cite the most important examples.

• DFG Programme: Research Grants
• International Connection: France
• Cooperation Partners: Professor Dr. Sakir Amiroudine; Dr. Jean-Pierre Delville