关键词: CFD, 两级注入式射流混合器, 数值模拟, 变异系数

Abstract: In order to solve the problems of small mixing ratio and inaccurate mixing ratio of jet mixer, a two-stage injection jet mixer was designed. The method of computational fluid dynamics was used to numerically simulate the fluid flow characteristics of the two-stage injection jet mixer. According to venturi pipe design standards and combing with CFD to simulate and calculate the different nozzle diameters, best mixing diameters were obtained, which were 9 and 21 mm, respectively. Using a four-factor and four-level simulation design, the influence of different throat lengths, expansion tube short axis lengths and diffuser tube angle  on the uniformity of the mixer outlet surface were explored. The simulation results showed that when the length of the primary throat was 45 mm, the length of the secondary throat was 80 mm, the short axis length of the primary jet expansion tube was 26 mm, and the angle of the secondary jet diffusion tube was 7°, the coefficient of variation was the smallest and the best mixing uniformity. And then the influence of different mixing ratios on the mixing coefficient of variation of the mixer was simulated and analyzed, and it was concluded that the two-stage mixer  achieved the same mixing effect under different mixing ratios. According to the optimized simulation results, the test data of different flow rates and mixing ratios were selected to compare the mixers. The test results showed that the maximum error between the test value and the actual value of the same mixing ratio was 3.5%, and the mixing coefficient of variation was all below 0.041 2, which indicated that the mixer could achieve a better mixing effect when the mixer was from 300∶1 to 3 000∶1. The maximum error between the simulated value and the experimental value of the same mixing ratio was 12.1%, which proved that the two-stage injection jet mixer meets the design requirements.

Key words: CFD, two-stage injection jet mixer, numerical simulation, coefficient of variation