Author(s): Humberto Salinas Tapia; Juan Antonio Garcia Aragon
Linked Author(s):
Keywords: Sediments; Turbulence; Settling velocity; PTV; Drag coefficient; Particle size. I
Abstract: Settling velocities of sediment particles for different size ranges were measured in this work using PTV. An experimental channel 10 cm x 15 cm cross section was used in order to obtain settling velocities for individual particles in three ranges of sediment sizes. The purpose is to analyze the effect of turbulence on the drag coefficient of solids settling velocity. The technique allows us to measure the individual settling velocity of the particles and the fluid velocity field. Capture and image analysis was performed with digital cameras (CCD) and Particle Tracking velocity (PTV) method. Software was developed to define particle sizes taking into account the particle image centroid of non-spherical particles. The algorithm allows particle discrimination by means of the different grey levels that a particle image presents and was developed for the purpose of this research. The algorithm is able to identify particles and to separate phases with a large difference in size and shape distribution. Results show that settling velocity of particles is affected by fluid turbulence which enhances the fluid drag coefficient. Physical explanation of this phenomenon is related with the magnitude of the vertical fluctuating velocity of the fluid. A correction to Dou (1963) coefficient for non-spherical particles settling in quiescent fluid is proposed in this work for a fluid Reynolds number (Ref) of 4250.
Year: 2007