A study on shear coagulation and heterocoagulation

Abstract

Coagulation and heterocoagulation of spherical particles in a simple shear flow have been studied by means of trajectory analysis. Effects of particle size and size ratio have been extensively examined. Some new features of shear coagulation and heterocoagulation have been recognized. Primary and secondary shear coagulations differ in many aspects. The nonequatorial effective capture cross-sections can be attributed to the pure secondary shear coagulation. Shear stability can be low at small and large particle size ranges due to secondary and primary shear coagulation, respectively, with a high stability range at medium particle sizes. A second range of high stability may appear at even larger sizes. On the basis of relative coagulation rate, shear heterocoagulation between particles of the same material but different sizes may or may not be favored over the respective homocoagulations. In the case of primary coagulation, the two homocoagulations are favored over the heterocoagulation. The opposite is true in the case of secondary coagulation. In a suspension composed of particle species of different materials and different sizes, if the larger particles are less stable at an assumed same size with the smaller particles, the homocoagulation of the larger species is still favored over heterocoagulation in the case of primary shear coagulation. In the case of secondary shear coagulation, the heterocoagulation may be favored over the homocoagulation of the larger species, if the above mentioned stability difference is not very large, the particle size difference is not small, and the size of the larger particles is within a certain range.