The Influence of Swirl on the Particle Dispersion in a Pipe Expansion Flow
The characteristics of the dispersion of spherical glass particles in a swirling and non-swirling pipe expansion flow were studied by the application of the Phase-Doppler technique. This measuring technique allows simultaneous measurements of particle size and velocity and hence determination of the velocity characteristics of different sized particles in the size spectrum of the used particle material.
Furthermore, the air velocity was measured simultaneously by seeding the flow with very small spherical glass beads and applying a phase discrimination procedure. For the present inlet configuration and a swirl number of 0.47 a closed central recirculation bubble was established for the air flow. In comparison to the non-swirling case the annular recirculation region in the edge of the pipe expansion was considerably reduced due to the rapid spreading of the swirling, annular jet.
The measurements of the particle size distribution throughout the flow field for the non-swirling case showed no considerable changes of the particle mean diameter in streamwise direction. In the swirling flow, however, a separation of the particles was observed as a result of the combined action of radial transport, turbulent diffusion and centrifugal effects. This yielded an increasing particle mean diameter along the centerline of the flow field up to a location were finally all particles have been removed from the core region due to centrifugal forces.
KeywordsRecirculation Region Swirl Number Recirculation Bubble Transient Recorder Central Recirculation Zone
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