ON THE TRANSPORT OF A SUSPENDED PARTICLE IN FLOW-THROUGH THE ENTRANCEREGION OF A TUBE

The motion of a single, spherical particle, released at different radi al positions at the inlet of the entrance region of a straight circula r laminar flow tube (Re = 260), was studied theoretically. Radial migr ation of the particle, either toward the tube center or toward the tub e wall, was predicted. Based on the hypothesis that the particle exper ienced a lift force which was produced by the vorticity in the boundar y layer and a velocity difference between the center of the suspended particle and the fluid medium, an inertia-vorticity fluid dynamic mode l was formulated to analyze the particle radial motions. Computational flow dynamics (CFD) solutions obtained from a 9.8 mm diameter tube mo del included the resulting particle loci for three particle radii (a = 0.1 cm, 0.085 cm, 0.050 cm), with the particle entry at various radia l positions. The computation also covered a range of different particl e entry speeds. The results showed that the particle migrates toward t he tube center if it lags behind the medium in the core region; otherw ise, it migrates toward the tube wall. Additional flow experiments wer e conducted in a circular (2R = 10.2 mm), 300 mm long straight tube. A small polystyrene sphere (2a = 1.72 mm, density pp = 1.014 g.cm(-3)) was released at the inlet (X = 0, eta/R = 0.48) with two dimensionless release velocities (omega(p) = 0, and omega(p) > 1.0). The recorded p article traces agree will with the computational model.