Filtration of aqueous colloidal ceria slurries using fibrous filters – An experimental and simulation study

Abstract

Abstract A combined experimental and computational study of fibrous filters for removal of large hydrosols, essential to minimize defects during chemical mechanical polishing, was performed. Dilute aqueous suspensions of colloidal ceria particles, of known size distribution, were filtered and the filter efficiencies were measured for different particle sizes and pH, then converted to single fiber efficiencies. The particle size distributions were also measured for the influent and effluent streams. In a series of numerical simulations, the Navier-Stokes equation was solved for a single fiber using the ANSYS-FLUENT computational fluid dynamics commercial package. For dilute suspensions, the motion of the dispersed particles in the size range of 35–600 nm was tracked in the Lagrangian reference frame including the effects of hydrodynamic drag, lift, gravity, hydrodynamic retardation, Brownian, van der Waals and electric double layer forces. The electric double layer and van der Waals forces were incorporated in the calculations by developing a user defined function. Particular attention was given to the effect of Brownian excitations, as well as the electric double layer and van der Waals forces - which have been neglected in many of the previous models - on the overall fiber collection efficiency for different particle sizes and charges. The simulated fiber efficiencies and particle size distributions compared very well with experimental results.