New High-Temperature Heat Pump (> 250°C) upgrading industrial waste heat < 90°C by hybridizing thermodynamic cycles
Decarbonizing industry is crucial to mitigate the impacts of human activities on the environment. Particularly, high-temperature heat (> 250°C) needs are substantial and difficult to decarbonize because of the high amount of energy required. Thermodynamic cycles of Heat Pump (HP), such as Reversed Brayton (RB) cycle, allow for upgrading industrial waste heat to higher temperature usable by processes. However, the energy efficiency of HP to produce heat > 250°C from 100°C from 80°C waste heat with low energy consumption was developed in our laboratory.
This doctoral thesis offers to study an innovative high-temperature HP combining an AHT with a RB cycle. The concept consists of using the AHT to elevate the temperature level of waste heat to temperature > 100°C and provide it to the RB cycle to generate high-temperature heat > 250°C at a low energy cost. Thus, this hybrid system offers a solution to meet industrial needs in decarbonized high-temperature heat. The main challenges laying ahead are the selection of relevant coupling architectures, as well as the study and development of efficient thermal transfer interfaces.
This research work will require mastering modelling tools of thermodynamic cycles and heat exchangers. The thesis will also involve an experimental aspect, since validation of the numerical results on a laboratory test bench are expected.
Fe–Zeolite coupling in a fixed-bed catalytic reactor for the direct hydrogenation of CO2 into sustainable aviation fuel (SAF)
The thesis aims to maximize CO2 conversion yields towards Sustainable Aviation Fuels (SAF, C8–C16). Currently, direct CO2 hydrogenation over an iron-based catalyst predominantly produces short-chain olefins (C2–C4), which do not meet SAF specifications. The proposed approach is to combine an iron-based catalyst with a zeolite catalyst within a single reactor, thereby integrating olefin production via CO2 hydrogenation with their subsequent conversion into longer-chain hydrocarbons in the SAF range (C8–C16). The zeolites investigated will exhibit properties tailored to this objective while retaining conventional formulations compatible with process scale-up.
The objective of the thesis is to understand how the formation of long-chain hydrocarbons suitable for the SAF fraction can be promoted by combining iron-based and zeolite catalysts within a single reactor. Two research areas will be investigated to achieve this objective. The first will focus on short olefin oligomerization (ethylene, propylene, butylene), assessing the influence of operating conditions and the presence of by-products from CO2 hydrogenation on the distribution of the resulting hydrocarbons. The second will investigate the integrated CO2 hydrogenation and olefin oligomerization process, aiming to understand the interactions between the two reactions and identify operating conditions that maximize selectivity and yield towards SAF-range hydrocarbons. Particular attention will be paid to the effects of thermal gradients and heat transfer phenomena on catalytic performance, product distribution, and catalyst stability.
Modeling of flow regime transitions in horizontal and inclined pipes: dynamic aspects and scalability
Understanding fluid flows in the piping systems of industrial facilities is of crucial importance for their safety and operation. In accidental scenarios studied for the primary circuit of a pressurized water reactor (PWR), two-phase flows within pipes may occur, exhibiting a wide variety of regimes depending on the encountered conditions. The transitions between these different regimes (stratified, annular, slug, bubbly, etc.) under such conditions are the subject of extensive experimental and numerical research. In particular, system-scale thermohydraulic simulation codes, such as CATHARE, must accurately compute these regime transitions.
This thesis aims to improve the prediction at the system scale of two-phase flow regime transitions in horizontal or inclined pipes. The project is structured around three main objectives. The first objective seeks to better account for scaling and fluid transposition issues by investigating models that influence the stratified/intermittent and stratified/annular transitions, including interfacial friction. The second objective focuses on predicting the transition between bubbly and intermittent regimes by revisiting the modeling of bubble segregation and mixing, and by incorporating new experimental data. The third objective, directly related to the previous one, addresses the transient effects of regime transitions, particularly by exploring the use of interfacial area transport equations.
The software tools used will include the CATHARE code, while experimental data will be provided from CEA facilities and the literature.
Effects of turbulence and mixing on the interactions between a hydrogen-air flame and a spray
This project studies the interactions between a hydrogen-air flame and a water spray in the context of a severe accident (e.g., hydrogen release in a nuclear containment). The goal is to analyze how sprays influence flame propagation and generated overpressures, which can either inhibit combustion or accelerate it through turbulence and obstruction mechanisms.
The experimental program is divided into:
1/ Characterization of spray-induced turbulence (1 or 2 nozzles, in open air or confined vessel) using PIV (Particle Image Velocimetry).
2/ Study of combustion impact: comparison of flame dynamics (H2/air) with and without spray, measuring propagation speeds and overpressures.
3/ Numerical modeling: adaptation of CFD codes (e.g., WALL-HY) to simulate flame-droplet interactions, building on previous work (G. Gai’s thesis).
This work aims to provide reference data and a predictive model to assess hydrogen-related risks in the presence of spray systems.
Fragmentation of a liquid sheet subjected to a strong initial velocity gradient
When a shock wave reflects off the free surface of a metal sample, it interacts with geometric irregularities (treated as defects such as those caused by a machining tool). At sufficiently high pressures, the shock reflection, followed by the material's expansion into the surrounding medium, can trigger the high-speed ejection (several thousand m/s) of liquid-phase metal sheets from the free surface. These sheets stretch and fragment, creating a particle cloud that can interfere with certain experiments. This process is extremely difficult to characterize experimentally or simulate, as it occurs at challenging spatio-temporal scales and involves material fracture physics that current computational codes based on hydrodynamic equations cannot naturally reproduce.
This thesis aims to address this specific issue. Drawing notably on theoretical analyses, it seeks to incorporate fragmentation processes into simulations where the material, modeled using a continuum (hydrodynamic) approach, is subjected to very high strain rates. One of the objectives is to predict the size distributions of the particles resulting from sheet fragmentation as a function of their velocity and to compare these predictions with available experimental data.