Soutenance de thèse : Cong YOU

Contribution to the study of ejector expansion heat pump cycle: modelling and experimental approach

Doctorant : Cong YOU

Laboratoire INSA : CETHIL

Ecole doctorale : ED162 : Mécanique, Energétique, Génie Civil, Acoustique de Lyon

This research addresses environmental concerns in the Heating, Ventilation, Air Conditioning, and Refrigeration (HVAC&R) industry by exploring carbon dioxide (CO2) as an eco-friendly alternative. The challenges of CO2, including its low critical temperature and high critical pressure, lead to its predominant use in transcritical mode, resulting in significant irreversibility during expansion. To overcome this, the study proposes the substitution of conventional expansion valves with ejectors in the transcritical CO2 heat pump cycle.

The ejector accelerates high-pressure CO2 through a nozzle, facilitating the mixing of low-pressure vapor from the evaporator and improving pressure recovery. Scientific validation confirms a reduction in compression work, establishing the ejector-based configuration as a more efficient alternative. Despite potential advantages, ejectors introduce complexities related to two-phase flow and sonic shock waves, necessitating simulation and experimental studies for enhanced performance.

The thesis conducts a comprehensive investigation, beginning with a review of refrigerant trends and a comparison of ejector technology with alternatives. Thermodynamic models are introduced, addressing key aspects such as isentropic efficiency, with novel data post-processing techniques proposed. The research introduces a 1-D homogeneous equilibrium model for the ejector region, validated and applied for parametric analysis and geometry design. This model is compared with 0- D thermodynamic models. Additionally, an experimental test facility provides insights into ejector performance across varying evaporation pressures.

In summary, this research significantly contributes to understanding transcritical CO2 heat pump cycles, specifically focusing on ejector technology. The integration of theoretical models and experimental studies offers essential insights for optimizing ejector design and operational parameters, meeting the evolving needs of the HVAC&R industry and promoting sustainable refrigeration applications.