The inclined settling of dispersed suspensions of spherical particles in square‐section tubes

Abstract

Abstract It has been known since 1920 that thing a tube containing a suspension increases the settling rate. The theory of Nakamura and Kuroda is shown to predict both an experimental and theoretical upper limit to this improvement. A small square‐section tube resting on an edge or on a corner is used to study the sculling of suspensions of closely‐sized spherical particles, four concentrations being used at five inclinations to the vertical. The initial settling rate shows no improvement over that obtained in a vertical tube, but a clarified layer is soon formed on the upper inclined face. Hydrodynamic forces then develop which transfer this liquid to the upper surface, thus augmenting the natural settling rate by factors as great as six or seven for the present tube geometry. By introducing a parameter to allow for the resistance to flow within the clarified layer, it is possible to predict the observed behavior on a theoretical basis. In particular, the effect of the concentration of the solid particles on the shape of the settling rate curves is shown to be a logical consequence of the properties of the system.