Effects of the nozzle contraction angle on particle flow behaviors in a gas-particle two-phase jet

The particle dynamics of a conical jet with different contraction angles (the cone angle of the contraction wall, α = 20°, 40°, 60°, 80°) were investigated using particle image velocimetry (PIV) and optical fiber probes. The axial and radial distributions of particle-phase velocity and concentration were measured within a confined chamber at the mass loading ratio mp = 0.3–3.3 and jet Reynolds number Re = 11,843–104,497. Due to the nozzle contraction effect, the particle dynamics of conical jet are significant differences from the pipe jet and the smooth contraction jet. In the axial direction, there is a strong slip velocity between two phases near the nozzle exit (x/D = 0–6), which leads to the occurrence of particle acceleration. In the radial direction, the particles preferentially converge towards the centerline, forming the particle contraction, which intensifies the momentum transfer from the axial to radial direction and thus increases the particle dispersion. The particle acceleration and contraction are more pronounced with the increase of contraction angle. Furthermore, the order of the velocity decay rate and the spreading rate for different contraction angles are 40° > 80° > 60° > 20°. The nozzle contraction angle of 40° shows the best entrainment and mixing characteristics. In addition, the particles contraction near the nozzle exit as well as the particles accumulation in the wall region (r/R = 0.83–1.00) increase the non-uniformity of particle concentration.