| The goal of this work was to assess the mechanisms of micron-scale particle removal from surfaces using a critical particle Reynolds number (Repc ) approach. The particle Reynolds number (Rep) describes the flow near an adhering particle and is defined as Rep=drVp m where d is the particle diameter, ρ is the fluid density, Vp is the relative velocity between the fluid and the particle at the center of the particle, and μ is the fluid viscosity. In this approach, particle removal occurs when Rep ≥ Repc, where Re pc is a function of the fluid forces, the geometry of the interacting objects, the removal mechanism, and the particle-surface adhesion force, which is a function of system composition, geometry, morphology, and deformation.; The Repc model was validated first using data found in the literature and then experimentally. The literature provided data for the removal of monodisperse glass spheres from a glass surface in laminar channel flow while the experimental work provided data for the removal of polydisperse polystyrene spheres from a quartz surface in laminar channel flow. In both instances, an experimentally validated adhesion model was used to predict an adhesion force distribution which was then used to determine Repc. Results indicated that rolling is the controlling removal mechanism and both studies showed that the predicted (rolling) adhesion profiles were in good agreement with the data when variation in particle size, adhesion force, and point around which rolling occurs was considered.; The Repc model was then used to analyze the removal of asymmetrical alumina particles from polished silicon dioxide and copper during brush scrubbing at operating conditions typical of commercial brush scrubbers. This analysis showed that (1) the time-dependent nature of the flow significantly affects particle removal in this system; (2) particle shape and the fraction of a particle embedded in a surface have a significant effect on particle removal by affecting both the particle-surface adhesion and fluid forces; and (3) brush-particle interaction may increase the percentage of particles removed by reducing the ‘effective’ particle-surface adhesion force and through brush-particle momentum transfer. |
