The ejector has been the research subject in the literature as the main component of refrigeration cycles using “thermal compression” thanks to its simplicity without moving parts. It uses a high-pressure fluid called “primary fluid” to drive and compress a low-pressure fluid, which is called “secondary fluid”. The performance of the ejector is defined by the entrainment ratio, which is the mass-flow ratio between the secondary and primary flows; as well as the critical pressure, which limits the operating range of the ejector. Most of the numerical and experimental studies have been conducted on water vapor ejectors. The studies showed that the geometry optimization is crucial in order improve the ejector performance. Moreover, experiments showed that the flow inside an ejector is often supersonic and highly compressible therefore inducing strong pressure variation. This can induce strong temperature variations and the apparition of liquid water and ice in ejectors have already been witnessed.

Numerical studies carried out previously have shown the importance of accurately modeling the liquid-vapor phase changes in order to establish consistent and accurate numerical models for flows hydrodynamics within the ejector. However, these studies give little or no consideration to the temperature field distribution within the ejector. The main difficulty here are the huge pressure variations that happen inside the ejector which lead to liquid vapor phase changes in a highly compressible flow. In this PhD project, we aim to investigate innovative solutions with ejector integrated into thermodynamic cycles working with natural fluids (ammonia, water, CO2 …) in order to improve the global performances. For this, it is important to understand the local physical phenomena of the flows inside an ejector, especially the impact of liquid-vapor phase change as well as the impact of the operating conditions.

Based on the strong research background of both CEA and INSA Lyon, we will conduct numerical and experimental works about the ejector and the thermodynamic cycles with the following research plan:
* Numerical work:
_ Development of a 1D model and perform the CFD simulations for comparison
_ Modelling and simulations of the identified thermodynamic cycles integrated the appropriate ejector
_ Design of ejector for tests
*Experimental work : fabrication of test ejector and perform measurements for model validation and analysis

For more than 15 years, CEA has conducted extensive research on thermodynamic cycles in order to develop innovative solutions for production of heat, cold and electricity. Recently, we have developed a new model of ejector for integration into a thermodynamic cycle . To bring new insight about the local phenomena of the flows inside an ejector considering the liquid-vapor phase, we have investigated and performed CFD simulations. INSA Lyon has strong research background on the topics related to CO2 such as heat pump cycles, heat exchangers as well as ejector. The test bench of ejector at INSA Lyon together with the INES platform at CEA will be served for the experimental work of this project.