Charge transfer by collision

Charge transfer occurs when particles collide with each other or with a solid wall. For monodispersed dilute suspensions of gas-solid flows, Cheng and Soo (1970) presented a simple model for the charge transfer in a single scattering collision between two elastic particles. They developed an electrostatic theory based on this mechanism, to illustrate the interrelationship between the charging current on a ball probe and the particle mass flux in a dilute gas-solid suspension. This electrostatic ball probe theory was modified to account for the multiple scattering effect in a dense particle suspension [Zhu and Soo, 1992]. 

Consider the charge transfer between two spherical particles of diameters dpi and dp2. A direct analogy between the charge transfer by collisions and the heat transfer by convection appears to be in order. Thus, the current density through the contact area of these two 

For each isolated particle, the charging current can be related to the particle capacity. Thus, we have 

From Eq. (2.74), the relationship between the contact radius rc and the approaching distance a for elastic collision of particles can be given by 

From Eq. (2.135), we obtain the relation of the contact time t and the approaching distance a as 

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In this chapter, various forces affecting the motion of a gas-solid flow along with the momentum equations governing the motions of particles are delineated. The mechanisms of charge generation and charge transfer by collisions of particles are discussed. 

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