Drag on non-spherical particles in viscous fluids

Abstract

The terminal settling velocity of several cylinders (of stainless steel, perspex and glass), needles (of steel) and rectangular prisms (of perspex) falling with their major axis parallel to the direction of motion has been measured in three Newtonian liquids. The measurements have been carried out in three to four fall tubes of different diameters to correct the measured terminal velocity for wall effects. The experimental results reported herein embrace the following ranges of conditions: particle to fall tube diameter ratio: 3.17 × 10^-2 to 0.776; length to diameter ratio for cylinders and needles: 5 to 50; the sphericity of particles: 0.35 to 0.7 and particle Reynolds number: 0.095 to 400. Terminal velocity data (corrected for wall effects) have been correlated using two approaches, namely, the usual drag coefficient-Reynolds number relationship, and in terms of a dimensionless velocity factor denoting the departure from the behaviour of an equivalent sphere. Predictive expressions have been developed using both schemes. Finally, the paper is concluded by presenting detailed comparisons between the present results and the prior investigations available in the iterature.