Adhesion moment model for estimating particle detachment from a surface

In this paper particle detachment from a surface by a hydrodynamic moment is analyzed. The detachment occurs when this moment exceeds the moment exerted on the particle by surface forces. An expression for the moment of surface forces is derived from the existing adhesion models. This moment is a product of the force acting on the particle and the variable contact radius, which decreases when the applied force increases. Accordingly, a condition for particle detachment from a smooth surface is obtained. In addition, particle detachment from a rough surface is considered. We show that a single-asperity contact is similar to the contact of a particle with a smooth surface, but the detaching moment is reduced, because of the lower adhesion force and smaller contact radius. We also consider a particle in contact with two and three asperities, and obtain a condition for particle detachment from a rough surface. It is also shown that the hydrodynamic moment can cause particle detachment, while the hydrodynamic lift force is smaller than the adhesion force by several orders of magnitude. On the other hand, the lift force exceeds the weight of the particle. Hence, the detached particle is eventually removed from the surface by this force.