Study on the mixing characteristics of coaxial swirl static mixer for hydrogen blending in natural gas pipeline

In this paper, a new type of static mixer structure is proposed for hydrogen and natural gas mixture pipeline, which has the characteristics of coaxial flow shear and swirl mixing with improved mixing of hydrogen and natural gas. The computational fluid dynamics model using large eddy simulation of the mixing process was established by comparing the simulation results with different sub-grid scale models against the experimental data. The mixing characteristics of the static mixer were analyzed in depth, and the effects of key parameters such as cavity number, torsion angle, swirl direction and swirl tube length on mixing performance were studied. The results show that the mixing intensity of the coaxial swirl static mixer increases first and then decreases with the increase of the number of cavities. The torsion angle mainly affects the uniformity of mixing, and the rotation direction of the swirl tube and the arrangement of the cavity have the greatest influence on the mixing effect. The mixing intensity is the highest when the double-layer cavity is arranged in opposite rotation direction, while the length of swirl tube has little effect. These results help to understand the mixing process of static mixer, and provide an important theoretical reference for the structural optimization design of static mixers. • CSSM is developed to integrate swirl tubes with coaxial shear flow. • Optimal cavity count balances mixing intensity and pressure drop. • Opposite swirl directions maximize turbulence through shear. • The torsion angle affects the mixing uniformity.