Theoretical background and experimental results
Dimensional hydraulic classification

Various flow regimes of the fluid around the solid govern the movement of the particles, opposing them with a resistance that varies with the relative velocity of the solid in relation to the fluid. These are defined (figure 1) [1]:

• a laminar or Stokes regime (figure 1a ) when relative motion is slow; the liquid threads, motionless in contact with the particle, are driven by a velocity that increases with distance from the particle, and each slides over the neighbouring threads, slowed down by the forces of viscosity,...