Transcritical single-phase CO2 ejector geometry optimisation by means of a multi-objective evolutionary algorithm and CFD models.

The effort made by researchers and companies to reduce the expected increment in the energy demand for cooling and air conditioning has arisen an interest in the ejector cooling cycles. Several typologies of ejector cooling cycles have been proposed by many researchers. However, the Coefficient Of Performance achieved by this type of cycles is still poor, mainly due to the poor ejector performance. Besides, the requirements imposed by the European Commission with the F-Gas Regulation have attracted extensive attention to the natural refrigerant CO2 for low and medium temperature applications. Trans-critical CO2 cycles, including ejectors, is a technology already being implemented but still with room for improvement. The objective of this work is to optimise the efficiency of a single-phase CO2 ejector by means of a Multi-Objective Evolutionary Algorithm coupled with a CFD model in which a real gas model has been implemented. The results showed a potential increment of 28% and 10% in the back pressure and the entrainment ratio, which are key parameters in the ejector efficiency.