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Numerical optimization on the geometrical factors of a subsonic air-air ejector HU Jian,CAO Xiaxin, HE Haisha, MENG Zhaoming, and DING Ming1   1. College of Nuclear Science and Technology, Harbin Engineering University, Harbin, China (E-mail: dingming@hrbeu.edu.cn)   Abstract:Theejectors can increase fluid pressure without directly consuming mechanical energy. They are widely used in many fields such as vacuum systems, refrigeration systems, fuel cells, chemical industry, aerospace and even core cooling systems of nuclear power plants. Although the structure of the ejector is simple, its internal flow field is very complex. Most existing design theories use semi-empirical and semi-theoretical methods. The design results deviate from the optimal structure, and a complete ejector size cannot be designed. In this study，the computational fluid dynamics (CFD) software, STAR-CCM+, was employed to investigate the effects of the geometrical factors of subsonic air-air ejectors. The mesh profile with 65669 elements has been proven to be sufficient to represent the ejector flow field. To investigate the accuracy of the numerical model, the experimental results and numerical simulation results were compared, which were in good agreement. The geometrical factors, such as the position of the nozzle, the ratio of the mixing chamber section area to the nozzle outlet sectionarea, the length to diameter ratio of the mixing chamber and the angle of the diffuser, were obtained by numerical simulation to maximize entrainment ratio. The numerical results show that the optimal position of the nozzle was 100 mm, the optimal ratio of the mixing chamber section area to the nozzle outlet section area was 35, the optimal length to diameter ratio of the mixing tube was 4 and the optimal angle of the diffuser was 4 degrees. Keyword:CFD; subsonic; air-air ejectors; geometrical factors
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