Free falling of non-spherical particles in Newtonian fluids, A: Terminal velocity and drag coefficient

The terminal velocity and drag coefficient are vital parameters for designing industrial systems involving freefalling particles. While the literature on spherical particles is abundant, that on non-spherical particles is scarce. Therefore, a comprehensive experimental study was conducted using discs, cylinders, and irregular particles of various sphericities in various fluids. First, the flow mode was analyzed, and seven flow modes were identified and described in a flow regime map. Subsequently, the terminal velocity and drag coefficient were correlated depending on the sphericity of three trends. The first is for nearly spherical particles with sphericities over 0.87, and the other two trend lines are for sphericities lower than 0.87, one for discs and the other for cylinders. Additional experiments enabled the extension of the models to nearly spherical, flat, and long particles within an error of +/- 30%.