for the modified Stokes velocity, where the constant 2.5 in Eq. (14-21) has been replaced by 5/3 and the constant k2 set equal to unity, based upon settling observations.

C. Coarse Particles

Coarser particles (e.g., ~ 100mm or larger) have a relatively small specific surface, so flocculation is not common. Also, the suspending fluid surrounding the particles is the liquid phase rather than a "pseudocontinuous" phase of fines in suspension, which would modify the fluid viscosity and density properties. Thus, the properties of the continuous phase can be taken to be those of the pure fluid unaltered by the presence of fine particles. In this case, it can be shown by dimensional analysis that the dimensionless settling velocity Vs/V0 must be a function of the particle drag coefficient, which in turn is a unique function of the particle Reynolds number, NRep , the void fraction (porosity), e = 1 — ', and the ratio of the particle diameter to container diameter, d/D. Because there is a unique relationship between the drag coefficient, the Reynolds number, and the Archimedes number for settling particles, the result can be expressed in functional form as

It has been found that this relationship can be represented by the empirical expression (Coulson et al., 1991)

where the exponent n is given by 4.8 + 2.4X

X = 0.043NAr57

0 0

Post a comment