Study on Flow Distribution and Structure Optimization in a Mix Chamber and Diffuser of a CO2 Two-Phase Ejector

This paper establishes a mathematic model of a CO2 two-phase ejector to investigate flow distribution in the components of a mixing chamber and diffuser. The suction chamber was modeled using the characteristic line method to describe the development process of the supersonic expansion wave, and the mixing chamber, as well as diffuser models, were built based on the double-flow model. The reliability of the model was verified by experimental data. The distributions of flow parameters along the axis of the mixing chamber and diffuser were analyzed under different expansion ratios of the ejector. Structure optimizations of the mixing chamber and diffuser were conducted. The results showed that the primary flow temperature gradually increased along the axis of the mixing chamber and diffuser, but the Mach number distribution decreased for a certain ejector expansion ratio. The temperature and Mach number of the secondary flow showed the opposite trend. Moreover, at the initial stage of mixing, the fluid pressure increased rapidly, and the Mach number of the primary flow decreased rapidly. The gas-phase fraction of primary flow increased gradually in the mixing chamber and was stable in the diffuser. When the length–diameter ratio of the mixing chamber was about 10.8–12, it was beneficial to mix uniformity, and when the expansion angle of the diffuser was 4–6°, the ejector had a better ejector efficiency.