Effects of the nozzle contraction angle on particle dynamics in a gas-particle two-phase confined jet

The particle dynamics of the gas-particle two-phase contraction jets were investigated to understand the particles dispersion and gas-particle mixing using the particle image velocimetry (PIV). The effects of nozzle contraction angles (α=20o, 40o, 60o, 80o) and gas jet velocities on the axial and radial velocity components of the particles and coherent vortices structures were discussed in a confined reactor. Compared with the pipe jet (without contraction), the nozzle contraction effect was found to result in a considerable axial slip velocity between particle and gas phase, which in turn accelerated the movement of particles. The radial velocity component formed due to nozzle contraction and increased with the contraction angle, made particles gather towards the jet axis, forming a diagonal impinging stream, which enhanced the momentum transformation from axial to radial directions. With the increase of gas jet velocity, the lag of particle velocity and interphase relaxation time increased, and the acceleration region moved towards downstream. The nozzle contraction intensified the instability of the shear layers, which made the shear layer oscillate and roll up to form axisymmetric vortex rings with large-scale and high-vorticity. © 2022 Zhejiang University. All rights reserved.