3D-flow simulation and optimization of a cross flow filtration with rotating discs

Abstract

The 3D-flow regime of a cross flow filter with horizontal rotating discs was examined. The influence of different shaped scrapers between the rotating discs on parameters like turbulence (k), dissipation (e) and overflow velocities were investigated by the commercial cfd program Fluent 5.0.2®. The main focus of the scrapers is to trigger off certain amounts of turbulence between the discs, that are necessary to avoid cake formation on the filter disc surface. Turbulence depends strongly on the rotation velocity of the discs. By modifying the cross sectional shape and the curvature of the scraper turbulence between two filter discs can also be influenced. The input parameters like the geometry and rotation velocity of the discs were altered. To understand the appearing swirls and flow characteristics of the model representing the real filter, simple models were simulated first. For all simulations the existing symmetries of the horizontal arranged filter discs could be used to simplify the geometrical models. The results of the simulation reflect the flow conditions in a rotating cross flow micro filter with cake limitation by scrapers with satisfying closeness. The usage of bent scrapers and the variation of scraper profiles lead to considerable improvements in the passing flow and turbulence situation in the region behind the scrapers.