Modeling coalescence in complex fluids

As part of the public-interest mission, IFPEN focuses on providing solutions to take up the challenges facing society in terms of energy and the climate. In particular one of the major concern of IFPEN is to reduce the cost and the environmental impact of the energy processes involving multiphase flows. Multiphase flows are encountered in many areas of the energy industry such as biomass conversion, and water treatment.  Liquid/liquid separation is frequently involved to separate a dispersed phase of a continuous phase. This process involves many physical phenomena at very different scales. The main difficulties in describing these phenomena stem from both the various scales involved in the flow but also from the different physics interacting at these scales (from the van der Walls forces acting at the molecular level to the hydrodynamic forces acting at the flow scale). The scale of interest to industry, here called macroscopic scale, is the separator one. However, physical interactions at the scale of interface between the two phases, governs the macroscopic behavior of the two-phase flow. Thus, to obtain an accurate modeling of large scale system, we should carefully address the small scales of fluid mechanics, but also take into account the forces acting at the molecular scale.
The resolution of all physical phenomena in macroscopic numerical simulations would require very fine meshes, which makes the calculation very costly or even impossible. At this scale, the phenomena that cannot be directly solved are modeled. The multi-scale approach proposed here consists in simulating the most relevant scale, and used simplified equations for the smallest scales. In this work we propose to carry out simulations at the microscopic scale, i.e. at the interface scale, using the free software Basilisk (http://basilisk.fr/), developed by Stéphane Popinet, wherein a VOF method associated with adaptive mesh refinement techniques and an efficient calculation of the surface tension enable to simulate accurately the evolution of the interface. The main objective of this thesis is to perform direct numerical simulations of a real emulsion into a multi-scale approach. In particular, a film drainage model to take into account the force at the molecular scale will be developed in Basilisk. Then simulation of an emulsion with a representative number of droplets will be performed in order to develop a multi-scale analysis. Following this analysis, subgrid models (frequency of collision between the drops, probability of coalescence) will be developed for the industrial scale.

Keywords: Coalescence, CFD, fluid mechanics,

• Academic supervisor    POPINET Stéphane (Senior researcher), ∂'Alembert, Paris
• Doctoral School    SMAER 
• IFPEN supervisor    Dr PIERSON Jean-Lou, jean-lou.pierson@ifpen.fr 
• PhD location    IFPEN Lyon, France  
• Duration and start date    3 years, starting in fourth quarter 2021
• Employer    IFPEN
• Academic requirements    Master degree fluid mechanics / applied mathematics
• Language requirements    Fluency in French or English
• Other requirements    Good learning of C programming language