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10 mars 2026 - Geometric optimization of heat exchangers and reactors combined with irreversibility minimization and equipartition theory / PhD Defense Shuxin Zheng
Doctorante : Shuxin ZHENG

Date et lieu : le mardi 10 mars 2026 à 14h00 dans l’Amphithéâtre du Cerege du Technopôle de l'Arbois-Méditerranée

Abstract: This study investigates the effect of geometry on the energy efficiency of heat exchangers and reactors by applying entropy generation minimization methods. In a concentric double-layer heat exchanger, four diameters are optimized while the exchanged heat is kept constant to determine the length in order to minimize the total entropy generation. The results show that optimized geometry reduces it. In addition, the study also investigates the influence of fluid flow rate on the irreversibility and the corresponding optimal geometry. In a double-layer tubular reactor with constant outlet reaction conversion, the entropy generation of the reactor is optimized by varying the reactor geometry of different shapes (cylindrical, conical, hyperbolic, sinusoidal). The effects of the heat fluid and the reaction mixture flow rate, the concentration and temperature of the reactants, and the reaction enthalpy on this irreversibility were also studied. A two-dimensional solution is used to analyze the distribution of the entropy generation rate with the help of COMSOL Multiphysics software. As a quantity associated with fluxes, the local rate is determined by the sum of contributions from heat exchange, viscous dissipation, and chemical reaction. This facilitates the comparison of the distribution of this local value and the driving force under the optimal and unfavorable geometries. The results show that in the optimal configuration, which minimizes the total entropy generation, the force and the local generation rate distributions are more uniform, which verifies the equipartition theory.

Keywords: Entropy generation minimization; Modeling; Equipartition

Jury
Erwin FRANQUET - Professeur Université Côte d’Azur - Rapporteur
Jean-François PORTHA - Maître de Conférences HDR Université de Lorraine - Rapporteur
Eric SCHAER - Professeur Université de Lorraine - Président du jury
Raphaele THERY - Maitresse de Conférences HDR INP Toulouse - Examinatrice
Jean-Henry FERRASSE - Professeur Aix-Marseille Université - Directeur de thèse
Olivier BOUTIN - Professeur Aix-Marseille Université - Co-directeur de thèse
6 février 2026 - Study of turbulent transport of energetic particles in nuclear fusion plasmas nuclear fusion plasmas by trajectory simulations and artificial intelligence techniques / PhD Defense Benoît Clavier
Doctorant : Benoît CLAVIER

Date et lieu : le vendredi 6 février à 14h00, M2P2 - salle Labus, Centrale Méditerranée

Abstract: This thesis studies the turbulent transport of charged particles in magnetized fusion plasmas by combining reduced turbulence models, numerical trajectory simulations, and data-driven approaches based on artificial intelligence. After presenting the physical framework of radial transport in a tokamak and the Hasegawa–Wakatani model, Eulerian and Lagrangian diagnostics are developed to obtain reference transport measurements. The work then analyzes the transport of test particles in different turbulent regimes, highlighting the limitations of certain classical approximations and the complexity of energetic particle dynamics. The study is extended to a more realistic three-dimensional ion-temperature-gradient (ITG) turbulence, allowing scaling laws for radial diffusion to be established. Finally, a synthetic turbulence generation model based on a Convolutional Variational Autoencoder (CVAE) coupled with a dynamic model is proposed to efficiently reproduce turbulence and accelerate transport studies, illustrating the potential of data-driven approaches for future research in plasma physics.

Jury
David ZARZOSO-FERNANDEZ - Chargé de recherche - CNRS M2P2 - Directeur de thèse
Emmanuel FRéNOD - Professeur des universités  - Université Bretagne Sud - Co-directeur de thèse
Victor TRIBALDOS - Professeur des universités - Universidad Carlos III de Madrid - Rapporteur
Julien LE SOMMER - Directeur de recherche - CNRS, IGE Grenoble - Examinateur
Maxime LESUR - Professeur des universités - Université de Lorraine - Institut Jean Lamour - Rapporteur
Mitra FOULADIRAD - Professeure des universités - Centrale Méditerranée - Président

22 janvier 2026 - Study of Combustion Instabilities Using Lattice-Boltzmann Methods / PhD Defense Ziyin Chen
Doctorante : Ziyin CHEN

Date et lieu : le jeudi 22 janvier 2026 à 13h45; amphi No.1 de Centrale Méditerranée

Abstract: Driven by climate change and the energy transition, hydrogen has emerged as a promising alternative to fossil fuels due to its efficient, carbon-free combustion. However, hydrogen–air flames exhibit strong instabilities, which are amplified in confined environments where wall effects and heat losses play a key role. Understanding these phenomena is essential for the safe design of micro-scale combustion devices.

This thesis investigates the stability of premixed hydrogen–air flames in a Hele-Shaw burner using the Lattice-Boltzmann method. Hydrodynamic and thermodiffusive instabilities are analyzed in both two- and three-dimensional configurations, with and without heat losses at the walls. The simulations reveal the conditions for symmetry breaking and quantify the influence of the Lewis number, channel width, and wall heat losses on flame morphology and propagation speed. Reduced-order models are developed to predict flame front geometry, cusp formation, and flame speed evolution.

These results improve the understanding of confined hydrogen flames and provide predictive tools for the design of safe and efficient micro-combustion systems.

Keywords: Flame instabilities, Laminar flame, Confined flow, Hele-Shaw burner

Jury
Carmen JIMENEZ ; CIEMAT, Madrid ; Rapporteure
Laurent SELLE ; CNRS IMFT, Toulouse ; Rapporteur
Andrea GRUBER ; SINTEF, Trondheim ; Examinateur
Heinz PITSCH ; RWTH Aachen University, Aachen ; Examinateur
Luc VERVISCH ; INSA Rouen Normandie, Saint-Etienne-du-Rouvray ; Président de jury
Pierre BOIVIN ; CNRS M2P2 ; Directeur de thèse
Christophe ALMARCHA ; Aix-Marseille Université ; Co-Directeur de thèse
Bruno DENET ; Aix-Marseille Université ; Co-Encadrant de thèse
13 janvier 2026 - Hybrid Lattice-Boltzmann method for multiphase flows / PhD Defense Thomas Gregorczyk
Doctorant : Thomas GREGORCZYK 

Date et lieu : le mardi 13 janvier à 14h00, amphi n°3 de Centrale Méditerranée

Abstract: The goal of this PhD is to present new numerical schemes that are able to carry out multiphase flows simulations. The method will lie in the framework of Lattice-Boltzmann methods that have been actively developed at M2P2 for several years for different applications : compressible flows, reactive flows, detonation, fluid-structure interaction, ...
This work aims at creating a stable scheme for athermal configurations at different density ratios and Reynolds numbers. Recent progress from the lab will be added to the multiphase LBM framework : a hybrid scheme solving an Allen-Chan with a finite volume solver, low-Mach number approximation, conservative scheme.

These new models will be tested thanks to different methods. First, we will make sure analytically that our scheme converges to a relevant set of macroscopic equations. Then, we will test these schemes against classical academical test cases such as : Poiseuille, Laplace, Rayleigh-Taylor, ...

The final target test case will be a jet which requires high Reynolds number flows simulations, inlet / outlet boundary conditions and which is useful for a wide range of applications.

Jury :
Raphaël LOUBÈRE, Rapporteur, DR CNRS, Institut de Mathématiques de Bordeaux 
Timm KRÜGER, Rapporteur, PR, University of Edinburgh                   
Gauthier WISSOCQ, Examinateur, IR, CEA CESTA                                 
Bénédicte CUENOT, Examinatrice, Senior Scientist, CERFACS                     
Vincent MOUREAU, Président du jury, DR CNRS, CORIA                                
Pierre BOIVIN, Directeur de thèse, CR CNRS, M2P2                                 
Song ZHAO, Co-encadrant de thèse, IR CNRS, M2P2            

11 décembre 2025 - Valorization of Pig Manure through Hydrothermal Treatment: Investigation of P and N Conversion Dynamics / PhD Defense Carolina Ochoa-Martinez
Doctorante Carolina OCHOA MARTINEZ

Date and location: Thursday, December 11, 2025, at 2:00 PM in the Forum projection room ; Arbois-Méditerranée

Abstract: Global agriculture relies heavily on non-renewable phosphorus (P) reserves and energy-intensive nitrogen (N) fertilizers to sustain crop production. At the same time, intensive livestock farming generates large volumes of liquid effluents rich in organic matter and nutrients, which, if not properly managed, can lead to environmental impacts associated with their discharge. 
To address these challenges, hydrothermal treatment of real pig manure was carried out to investigate the influence of operating conditions on P and N conversion and distribution. Comparative experiments were performed across a wide severity range (107–200 °C, 25–95 min to 300 °C, 10–60 min). The resulting solid, aqueous and oil phases were systematically characterized through physicochemical analyses and sequential phosphorus extractions. 
Results show that more than 90% of P was recovered in the solid phase. The mineralization of organic P and Al/Fe-bound P dissolution into calcium phosphates was identified as the main mechanism governing P retention in the hydrochar. Temperature emerged as the most influential parameter affecting P conversion and speciation, with strong correlations observed between P forms and the availability of metal cations (Ca, Mg, Fe, Al). Dissolved organic nitrogen remained the dominant N fraction in the aqueous phase, highlighting a major limitation in current hydrothermal valorization strategies.

Keywords: Hydrothermal treatment, pig manure, phosphorus speciation, nitrogen transformation, biocrude, process water recirculation, hydrothermal liquefaction, hydrothermal carbonization.

Jury :
Audrey VILLOT                                          Rapportrice,                                                      IMT Atlantique
Magali CASELLAS                                     Rapportrice,                                                      Université de Limoges
Boram KIM                                                 Examinatrice,                                                    INSA Lyon
Stéphan BOSTYN                                      Examinateur,                                                     Université d’Orléans
Olivier BOUTIN                                          Examinateur,                                                     Aix Marseille Université
Jean-henry FERRASSE                            Directeur de thèse,                                            Aix Marseille Université
Cristian BARCA                                        Co-directeur de thèse,                                       Aix Marseille Université
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