Release of non-Brownian particles

The release of non-Brownian particles (diameter s 5 pm) from surfaces has been studied. The influence of several variables such as flow rate, particle size and material, surface roughness, electrolyte composition, and particle surface charge has been considered. Experiments have been performed in a physically and chemically well-characterized system in which it has been observed that for certain particle sizes there exists a critical flow rate at which the particles are released from surfaces. This critical flow rate has been found to be a function of the particle size and composition. In addition, it has been determined that the solution pH and ionic strength has an effect on the release velocity. 

In this investigation we experimentally determine the factors controlling the release of non-Brownian particles. Also, we discover the initial particle release mechanism, (i.e., rolling-vs-sliding). 

A summary of the most important experimental findings of Chamoun (H), along with a description of the experimental apparatus and procedure, is presented in this chapter. In particular, the experiments have shown which factors (such as pH, ionic strength, etc.) control the release of non-Brownian particles and also have proven that the initial particle release mechanism is rolling rather than sliding. 

The release or detachment of the fine particles from the collector surface is assumed to be induced by the hydrodynamic forces in the case of non-Brownian particles or by the colloidal forces in the case of Brownian particles [131]. For non-Brownian fine particles, the rate of hydrodynamic particle entrainment is considered to be proportional to the difference between the wall shear stress and the critical shear stress [123] ... 

For the purpose of this study, particles are classified as Brownian or non-Brownian, where Brownian particles are defined as those for which the diameter is less than five microns and non-Brownian are those with diameter greater than five microns. The major focus of this work is on the second category. The particle release process has been studied both theoretically and experimentally, and it is found that for non-Brownian particles the surface charge and the electrolyte composition of the flowing phase are less significant factors than the hydrodynamic effects. However, Van der Waals forces are found to be important and the distortion of particles by these forces is shown to be crucial. 

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