Particle Velocities in a Swirling, Confined Flow

Abstract

Abstract Abstract— Measurements of velocity have been obtained by laser-Doppler velocimetry in the isothermal flow of liquid in an axisymmetric vessel of geometry similar to that of a quarl burner and furnace. The arrangement comprised a co-axial jet, a diffusing quarl, a sudden expansion, a length of constant-diameter pipe and a contraction to the exit pipe. The liquid was a mixture of tetraline and turpentine with concentration and temperature arranged to match its refractive index to that of the plexiglass vessel and to plexiglass beads. with mean diameters of 510 and 700 μm, used to allow examination of two-phase flows. With single-phase flow, the swirl number of the annular jet was 1.38 and the ratio of the mass-flows in the central pipe and annulus was varied from zero to 0.77 to allow examination of the resulting flow characteristics with emphasis in the quarl region. The results quantify the decrease in size of the toroidal vortex with increasing mass-flow in the central jet and the correspondingly more uniform velocity distribution in the down stream region. The plexiglass beads were added separately to the core and annulus flows for the case of equal bulk mean axial velocity (a mass-flow ratio of 0.25 in the central pipe) and the single refractive index of the vessel, liquid and beads allowed measurements with mean volume concentration up to 0.113 and limited by the depth of field and inclusion of gas within the beads. With beads in the central jet and a volume concentration of 0.004, the bead velocities are higher than that of the single-phase flow by up to 15% up to the axial location where the swirl and geometry induce the toroidal vortex and low centreline velocities after which the beads tend to lag. With beads in the annulus of mean concentrations up to 0.113, the swirl causes locally high concentrations with a less uniform annulus velocity profile and considerable suppression of turbulence. In both cases, the profiles of mean and rms velocities were similar for beads and single-phase flow in the downstream region.