where g is the gravitational acceleration (9.81 m/s2), dp is the particle diameter (m), ρp and ρ are
the density of particle and liquid, respectively (kg/m3), CD is the drag coefficient
(dimensionless), and μ is the liquid viscosity (kg/m/s). The granules usually have a spherical
form but they are not smooth or rigid, and thus CD for the granules is higher than that of smooth
rigid spheres