Experiment on settling of slender particles with large aspect ratio and correlation of the drag coefficient

The drag coefficient of slender particles is an important parameter to operations involved with them. In this paper, settling of slender particles with a large aspect ratio and of different materials in laminar Newtonian fluids is studied. It is observed that the particle orientation oscillates during settling and stabilizes to its equilibrium horizontal orientation eventually. Experiments are conducted in different fluids (water and glycerin solutions, quiescent or flowing) for particles with different densities (from 1125 to 8000 kg(.)m(-3)) and aspect ratios (from 4 to 50). It is found that the product of the drag coefficient and cosine of the orientation angle is independent of the particle aspect ratio and the bulk liquid flow. Instead of using the concept of sphericity, the drag coefficient of slender particles is effectively correlated with the orientation and the Reynolds number based on the particle cylindrical diameter. With the aid of the modified Archimedes number, the proposed general correlation C-D cos phi = (24/Re)(0.006983 + 0.6224Re(-1.046))-(rho(p)/rho(l))(-1.537)(Ar*)(0.8524) represents very well the experimental data under various experimental conditions with the average relative error of 9.4%.