Orthokinetic agglomeration

If colloids are sufficiently large or the fluid shear rate high, the relative motion from velocity gradients exceeds that caused by Brownian (thermal) effects (orthokinetic agglomeration). 

Both modes can occur in precipitation processes, but in a stirred precipitator orthokinetic agglomeration clearly predominates. From the Smoluchowski kinetic expressions for perikinetic and orthokinetic agglomeration it can be deduced (Sohnel and Mullin, 1991) that the relationship between agglomerate size D and time t may be expressed by... 

TJhe aggregation of particles in a colloidal dispersion proceeds in two distinct reaction steps. Particle transport leads to collisions between suspended colloids, and particle destabilization causes permanent contact between particles upon collision. Consequently, the rate of agglomeration is the product of the collision frequency as determined by conditions of the transport and the collision efficiency factor, the fraction of collisions leading to permanent contact, which is determined by conditions of the destabilization step (2). Particle transport occurs either by Brownian motion (perikinetic) or because of velocity gradients in the suspending medium (orthokinetic). Transport is characterized by physical parame-... 

The overall rate of agglomeration of any suspension, that is prepared experimentally and consists of small and large colloids, is obtained by adding the expressions derived for perikinetic and orthokinetic coagulation (Equations 2 and 5) ... 

From a comparison of the two collision frequency terms, described in detail in the Equations 3 and 6, one obtains the relative contributions of the perikinetic and orthokinetic transport to the total particle agglomeration. The ratio is a function of the radius of the colloid, r, and the absolute value of the velocity gradient du/dz ... 

Acoustic agglomeration is a process in which acoustic forces cause particles to interact and, eventually, to collide. The complex mechanisms behind this process involve orthoki-netic and hydrodynamic interactions. The orthokinetic interaction is founded on the hypothesis that collisions are produced due to the different acoustic entrainments experienced by particles of different size and weight. In order to describe this mechanism, an agglomeration volume is defined around each particle as a volume where another particle can be captured [49], However, this mechanism, which constitutes the basis for most existing interaction models, can explain neither the agglomeration of monodispersed aerosols nor the way in which the agglomeration volume is refilled once the initial particles are captured. 

Orthokinetic, where agglomeration is dominated by convection. That is, the particles are transported by movement of the surrounding fluid (78). The analysis of Smoluchowski, which was limited to laminar shear flow, was extended to turbulent flow by Saffman and Turner (79)... 

The agglomeration kernel j3 depends on the mechanism of a lomeration and on the particle size (Figure 4.5). For small particles, the Brownian motion due to fluctuations in the solution suffices for an effective a omeration this is called orthokinetic a lomeration. For larger particles, a velocity gradient in the mother phase is necessary for particles to collide and thus to agglomerate, this is the perildnetic agglomeration. 

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