Enhancing gas-liquid mixing effect in pipelines: Experimental and numerical investigations of blind tee and traditional elbow

Blind tees, as typical upstream component for multiphase flow measurements, can promote the gas-liquid mixing in pipelines. However, detailed investigations on the mixing mechanism in blind tees are still scarce. This study employs a combination of experiments and numerical simulations on bubble flow in bend pipes to analyze twophase flow dynamics in both the traditional elbow and blind tee. Firstly, the swirling phenomena at the outlet of bending structures are revealed using the measured flow images, and the dominant modes of gas distribution are extracted with proper orthogonal decomposition method to conduct a low-dimensional spatiotemporal analysis. Then, the mixing mechanism and vorticity distribution in different bending structures are compared using numerical results. Finally, the influences of bending structures and gas-liquid flow conditions on the mixing performance are comprehensively assessed. Results indicate that blind tee has a better mixing performance than traditional elbow, which significantly improves the gas distribution uniformity at the bend outlet. With the increase of volume gas content, the vortex intensity and frequency at the blind tee outlet increase, resulting in an increase in the uniformity of gas distribution. Moreover, the blind tee exhibits a shorter distance of turbulence dissipation than the traditional elbow. Therefore, a more uniform and stable bubble flow can be obtained within the range of 6D-8D downstream of the blind tee.