Effect of Near-Wall Turbulence on Selective Removal of Particles From Sand Beds Deposited in Pipelines

摘要

This paper investigates the effect of near-wall turbulence on selective removal of small-size particulate matter from sand beds deposited in pipelines. In an effort to develop effective strategies for in-line fines separation, experimental data on selective particle removal by burst-sweep turbulent structures have been gathered. A3 3/4" (0.095 m) diameter-15 m long flow loop together with a particle image velocimetry (PIV) system has been commissioned and used for observations of turbulent burst activities. The flow loop was also equipped with bottom extractors to allow real time sampling of deposited particles which are then analyzed for determining particle size distribution changes with time. In this work, the alteration of size-composition during turbulent transportation of moving (sand) bed was assumed to be the effect of burst-sweep activity (coherent structures). The frequency of coherent burst structures was measured at various distances from the pipe wall, during the radial dissipation, and results were compared with existing literature. The experimental results indicated that when a bed of particles with 0.1-50 um size range is exposed to burst-sweep activities during turbulent pipe flow, the concentration of fine particles within the bed increases with time (i.e., coarser particles are preferentially removed).