The applicability of the pseudo-fluid model to the settling velocity of a foreign particle in a suspension

The pseudo-fluid model is a typical procedure applied to multiparticle suspensions wherein all the fluid and some of the solids are assumed to behave as an equivalent homogeneous fluid whose characteristics are chosen in such a way as to mimic a fluid dynamic effect on the remaining solids. The pseudo-fluid approach is discussed and has shown its applicability over a wide range of flow regime and solid and fluid physical properties. However, care should be taken when the size and the density of the foreign solid approaches that of the suspension solid, and when the fluid-solid mixture making up the pseudo-fluid is not homogeneous.