Description du sujet de thèse

Title: Integration of low environmental impact refrigerants. Study and development of innovative heat pumps using reactive fluids.

Summary of the topic:
In the context of energy transition and decarbonisation of residential heating, the development of high-efficiency, low environmental impact thermodynamic systems is a major priority. The choice of refrigerant used in heat pumps plays a central role in this evolution, influencing the energy performance, environmental footprint and regulatory compliance of the systems. This thesis is part of the 'Smartfluid' research project, coordinated by BDR Thermea in collaboration with the LRGP (Laboratoire Réactions et Génie des Procédés). This 48-month project aims to design a highly-efficient heat pump based on an innovative thermodynamic principle and intelligent on-board control, in order to improve its energy performance while actively reducing its environmental impact. The proposed doctoral work will aim to assess the technical, environmental and regulatory feasibility of using original alternative working fluids studied in this project, in residential heat pump systems.

The thermodynamic innovation of the project is based on the use of a fluid capable of undergoing a chemical dimerisation reaction, allowing a chemical energy component to be integrated into the heat pump cycle, thereby improving its overall efficiency.
In addition, this fluid is a natural refrigerant, offering a safer and more environmentally friendly alternative to propane and other commonly used synthetic refrigerants.

Methodological approach:
1. State of the art on working fluids and the regulatory framework.
An in-depth literature review will be conducted to identify current and emerging refrigerants used for residential applications. This study will focus on their thermophysical and chemical properties, their compatibility with existing equipment, and the associated regulatory constraints (e.g. F-Gas regulations, flammability, toxicity, safety classifications). This work will establish the scientific and regulatory context necessary for the development of next-generation refrigerants.
2. Modelling of a residential vapour compression heat pump using inert refrigerants.
Several conventional refrigerants, known as 'inert' refrigerants, will be studied using thermodynamic modelling tools developed in the laboratory. The aim is to evaluate their energy performance, thermodynamic limitations and suitability for residential use, in order to establish a basis for comparison with reactive fluids.
3. Modelling of a residential vapour compression heat pump using reactive refrigerants
A similar modelling approach will be applied to reactive fluids and their mixtures with inert components. The study will analyse the influence of chemical reactivity on system performance, component sizing and operating stability, with the aim of identifying the potential advantages and constraints associated with these new working fluids.
4. Theoretical evaluation of compressor performance with reactive fluids.
The use of reactive fluids can significantly affect compressor operation. This section will assess the effects on thermodynamic efficiency, chemical stability, lubrication, material compatibility and mechanical wear. Particular attention will be paid to possible interactions between reactive species and compressor materials, as well as to possible mitigation strategies.
5. Analysis of the compatibility of materials and components with reactive fluids.
An in-depth analysis of potential interactions between reactive fluids and the materials used in the system (e.g. heat exchanger surfaces, seals, compressor components) will be carried out. The aim is to anticipate risks related to corrosion, material degradation or a reduction in component life.
6. Collaboration with BDR Thermea – design and testing of a prototype heat pump using the new reactive fluid and an inert fluid.
In collaboration with industrial partner BDR Thermea, a prototype heat pump incorporating the new reactive fluid (pure or mixed with an inert fluid) will be designed, manufactured and tested experimentally. This phase will validate the models developed and identify the main technical obstacles to be overcome for future industrial implementation.
7. Improvement of the internal code for simulating thermodynamic cycles.
The existing internal code for simulating thermodynamic cycles will be enhanced to take into account the behaviour of reactive fluids. Developments will include the possible integration of chemical reaction models, improved fluid property correlations, and the possibility of optimising cycles by taking into account new constraints related to chemical reactivity.

This research work should make it possible to:
- Better understand the potential and limitations of reactive fluids in residential heat pump systems;
- Develop robust predictive models adapted to unconventional working fluids;
- Provide technological recommendations for the choice of materials and components compatible with these new fluids;
- Contribute to the evolution of the regulatory framework for refrigerants with low global warming potential (GWP);
- Lead to the experimental demonstration of an innovative heat pump concept using alternative working fluids.

Research environment and opportunities
The PhD student will join a dynamic, multidisciplinary team involved in several ongoing scientific projects focusing on sustainable thermal and electrical systems, low global warming potential (GWP) refrigerants, and thermodynamic modelling.
Collaborations with other internal and external research teams will be encouraged, providing opportunities to interact with specialists in thermophysical property measurement, computational thermodynamics, and heat pump design.
The PhD student will thus gain valuable experience working in a team within a scientific environment that promotes innovation, knowledge sharing and applied research focused on the real challenges of the energy transition.

Required skills
- Cross-disciplinary skills: Strong critical and analytical thinking skills; Excellent scientific writing skills; Good time management and organisational skills; Ability to work collaboratively; Proactive and solution-oriented attitude.
- Technical skills: Solid foundation in mechanical and energy engineering; Proficiency in modelling and programming tools (e.g. Python, MATLAB or equivalents); Interest in applied thermodynamics, numerical simulation and sustainable energy systems.

Contexte de travail

The Reactions and Process Engineering Laboratory (UMR 7274) is a joint unit of the CNRS and the University of Lorraine, created on 1 January 2010 and based in Nancy. Its general scientific objective is to study processes in their entirety and complexity. The LRGP develops the scientific and technological knowledge necessary for the design, study, management and optimisation of complex physico-chemical and biological transformation processes involving matter and energy. The unit has more than 300 staff, including nearly 20 CNRS researchers, 80 teacher-researchers, 45 technical and administrative staff and 180 non-permanent staff (contract researchers, 85 doctoral students, post-doctoral students and master's students).

This research project will be carried out within the CiTherE research area, which is made up of specialists in chemical kinetics, thermodynamics and chemical reaction engineering. The fields of study are mainly focused on energy and aim to develop more efficient, economical and environmentally friendly energy systems through an approach combining physical chemistry and process engineering. The experimental and theoretical work carried out within this research area has led to an original approach that enables the understanding and modelling of phenomena at the molecular level to be transferred to the reactor or process level.

The position is in a sector covered by the protection of scientific and technical potential (PPST) scheme and therefore, in accordance with regulations, requires your arrival to be authorised by the competent authority at the MESR.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.