Destabilization of Particles by Turbulent Rapid Mixing

Destabilization of particles during coagulation is analyzed on the basis of collisions between colloidal particles and eddies of the size of the microscales of turbulence which carry the incipiently forming positively charged hydrolysis species. The theory developed indicates that minima in the destabilization rate occur at specific ratios of microscale size (η) to particle diameter (d1). For the viscous and inertial subranges of turbulence, these ratios (η/d1) are 2.0 and 1.33 respectively. They correspond to velocity gradients G¯ of 1,500-3,500sec-1 which should be avoided for 3 μm colloidal particles. The theory is validated by experiments on a direct filtration pilot plant using coagulants under charge neutralization conditions in a variable‐speed backmix type rapid mixer. The electrophoretic mobility and filterability number are the parameters used to confirm the minima in the destabilization rate. The study provides an underlying conceptual basis for the magnitude of the velocity gradients in rapid mix units used in practice. The theory provides a rationale for the design of rapid mixers on particle size distribution.