Vortex shedding of unsteady symmetric flow regime induced by secondary impinging in T-T jet reactors

Abstract

Fluid mixing is widely employed in the chemical industry, and the mixing efficiency is intensely dependent on the flow characteristics in the reactors. In this work, flow regimes in a T-T jet reactor were investigated by Planar Laser-Induced Fluorescence (PLIF) at 27 ≤ Re ≤ 600. Segregated flow, vortex flow, steady and unsteady engulfment flow, and unsteady symmetric flow are generated in mixing channel with the increase of Re. Particularly, vortex shedding phenomenon was observed in the Reynolds number range of 400–600 after secondary impinging, which changed the flow topology and thus significantly improved the mixing of unsteady symmetric flow in the T-T jet reactor. Unlike the unsteady symmetric flow in a classical T jet reactor, the impinging cone with oscillatory behavior was formed in the mixing channel to generate vortex shedding. Velocity field of unsteady symmetric flow in a T-T jet reactor under the effect of secondary impinging was obtained by Particle Image Velocimetry (PIV). The fluid exhibits a large velocity distribution in the region of the impinging cone, followed by a gradual decay of velocity along the mixing channel and accompanied by vortex shedding. The numerical results reveal the mechanism of the improved mixing of unsteady symmetric flow under the influence of secondary impinging. It is found that the formation of additional leg vortices and the merging between different leg vortices by secondary impinging are the key reasons for the vortex shedding phenomenon and the improvement of mixing.