Characterisation of the physico-chemical properties of solid residues from biomass hydrothermal carbonisation
Hydrothermal carbonisation (HTC) is a thermochemical conversion process performed in pressurized water (2-6 MPa) between 180 and 260°C. The main product is a carbonaceous solid residue (hydrochar). Various applications are foreseen for hydrochar: combustion, gasification, adsorption, catalysis, soils amendment, hard carbon for Na-ion batteries, …, each of them requiring specific properties.
The objective of the thesis is to characterise and better understand the origin of several physico-chemical properties of biomass hydrochars. A special attention will be paid to hydrophobicity and drying capacity, to physical and textural characteristics of the particles (porosity, granulometry, specific surface), as well as to chemical characteristics (composition). The influence of biomass type and HTC conditions on these properties will be investigated.
The approach will consist in: experimentations in batch reactors on pre-selected biomass resources, together with use of different characterisation techniques for hydrochars; analysis of results aiming at determining links between the characteristics, elucidating the links between the resource and its hydrochar properties as a function of operational conditions.
Integrated waste treatment: design and optimisation of a multi-waste treatment scheme for a multi-purpose energy production
At the city scale, multiple waste streams such as household waste, compost, sewage sludge, yard waste, non-recyclable plastics, used oils, metals, glass, and others. All of these feedstocks exhibit variable seasonality and carbon content. Nowadays, the aforementioned streams are managed through recycling, and in some cases incineration or landfilling. Alternative treatment technologies, such as gasification, hydrothermal gasification, and anaerobic digestion, are being explored as potential pathways to improve the overall sustainability of waste management.
Existing scientific studies have largely focused on the conversion of individual waste types or on the application of a single technology to a specific waste stream, without accounting for regional integration, resource variability or systemic assessment. A city-scale analysis of waste streams could enable the identification of synergies between different waste types and the identification of optimal conversion pathways.
In this context, a key scientific challenge lies in the development of an integrated, multi-waste treatment framework capable of modelling, optimizing, and assessing a multi-waste, multi-product energy system at the city scale. The objective of this PhD project is to investigate waste treatment at the city scale, accounting for the seasonality of waste generation, waste stream composition, and local energy demand (heat, electricity, and gas). The work will consider local and European regulations (Waste Framework Directive, AGEC law, and RED III directive) as well as techno-economic and environmental aspects. The study will focus on one to three representative geographic areas and will establish a methodology that can be further applied to a broad range of territorial contexts.
On the fluid distribution for liquid thermocline - From experimental work to reduction of models
Thermocline heat storage (stratified tank) is an industrial solution for recovering waste heat and integrating intermittent energy sources. However, its performance remains limited by poorly controlled phenomena: non-uniform fluid distribution, partial thermal cycling, and real-world operating conditions (fluctuating inputs, incomplete cycles).
The proposed doctoral research builds upon the PhD work of Alexis Ferré and the postdoctoral research of Martin Rudkiewicz, which focused on the modeling and characterization of thermocline storage systems. These studies led to the development and validation of a comprehensive physical model implemented in ANSYS Fluent, enabling detailed investigation of the physical phenomena governing the formation and subsequent transport of the thermocline within a storage tank.
A partially validated CFD numerical model, together with a fully operational experimental facility, will therefore constitute the foundation of this PhD project. The main objectives are:
• to further advance the experimental characterization of liquid thermocline storage behavior, with particular emphasis on the influence of flow distribution (including distributor type and design parameters), thermal cycling, and initial conditions on storage performance;
• to validate the CFD physical model against newly acquired experimental data;
• to reduce the high-fidelity CFD model to a comprehensive system-level model incorporating the distributor, the storage tank, and the extraction process;
• to provide the scientific and industrial communities with currently unavailable datasets that are essential for model validation under varied and realistic operating conditions.
Heat Transfer Enhancement by Convective Boiling in Microchannels applied to the Cooling of Computing Units in Data Centers
The proposed PhD thesis aims to improve the understanding and modeling of convective boiling phenomena in microchannels for new low-environmental-impact refrigerants. The candidate will adopt a combined experimental and multi-scale modeling approach, including the design of a test bench simulating the behavior of a micro-evaporator, the implementation of CFD simulations (ANSYS Fluent, CATHARE) to describe two-phase flow regimes, and the evaluation of various eco-friendly alternative fluids. The expected outcomes include, for each of these new fluids, the characterization of confined boiling mechanisms, the development of a predictive heat transfer model, and the proposal of innovative cooling solutions.
The growing demand for high-performance computing, driven by artificial intelligence and cloud technologies, leads to a significant increase in power dissipation in electronic chips. Current single-phase cooling technologies are reaching their limits when dealing with heat fluxes exceeding 100 W/cm². Two-phase cooling, based on fluid boiling to remove heat, can achieve much higher heat transfer performance than single-phase systems while reducing overall energy consumption. The results of this research will contribute to the development of more efficient and sustainable cooling solutions for future data centers, helping to reduce the digital sector’s energy footprint and strengthen European technological sovereignty in advanced cooling technologies.
Mechanical degradation of Solid Oxide Cells: impact of operating and failure modes on the performances
Solid oxide cells (SOCs) are electrochemical devices operating at high temperature that can directly convert fuel into electricity (fuel cell mode – SOFC) or electricity into fuel (electrolysis mode – SOEC). In recent years, the interest on SOCs has grown significantly thanks to their wide range of technological applications that could offer innovative solutions for the transition toward a renewable energy market. However, despite of all their advantages, the large-scale industrialization of this technology is still hindered by the durability of SOCs. Indeed, the SOCs remain limited by various degradation phenomena including mechanical damage in the electrodes. For instance, the formation of micro-cracks in the so-called ‘hydrogen’ electrode is a major source of degradation. However, the precise mechanism and the full impact of the micro-cracks on the electrode performances are still unknown. By a multi-physic modelling approach, it is proposed in this thesis (i) to simulate the damage in the microstructure of the electrode and (ii) to calculate its impact on the loss of performances. Once the model validated on dedicated experiments, a sensitivity analysis will be conducted to provide relevant guidelines for the manufacturing of improved robust and performant electrodes.
Thermodynamic and experimental approach of the reactivity in multi-constituted Silicon-Metal-Carbon systems for ceramic brazing
The development of ceramic-based material assemblies plays a fundamental role in technological innovation in many engineering fields. The choice of materials and joining process must ensure a functional, reliable and durable assembly, whose properties comply with the specifications of the application.
The PhD thesis is part of the development of brazing alloys optimized for the joining of ceramics (primarily silicon carbide) considered for various applications in harsh environments, particularly in the field of energy. Indeed, the design of these materials requires a good knowledge of the reactivity at the liquid alloy / ceramic interface. In this context, the thesis will contribute to the development of a thermodynamic and experimental approach to predict and understand the reactivity in multi-constituted Si-Metal-Carbon systems. This work includes a study of the wetting and interfacial reactivity of selected alloys (wetting and brazing experiments, fine characterization of the interfaces by different techniques such as FEG-SEM, X-ray diffraction, TEM, XPS) with the support of thermodynamic modelling using the CALPHAD method. This highly experimental work will be carried out in a dynamic and collaborative environment.