Numerical simulation of the flow in a rotating disk filtration module

Abstract

The characterization of the flow inside an experimental flat membrane module with a smooth rotating disk was performed. The module consists of a disk rotating at speeds up to 3000 rpm inside a cylindrical housing equipped with a stationary circular flat membrane. The characterization was carried out by using a finite volume CFD software with the κ- omega turbulence model and results of the range of rotation speeds 300 ≤ Ω ≤ 20000 rpm were compared with experimental and theoretical data reported in previous studies. The simulations suggest high permeate fluxes for the device due to large average shear stresses on the membrane and the absence of stagnant zones inside the module, which are desirable features to avoid membrane fouling processes. The simulations show an overall good agreement with theoretical results based on the main assumption that the wall shear stress on the membrane and on the disk can be predicted using modified correlations for rotating flow over a stationary wall and for flow induced by a rotating disk, respectively and with experimental pressure measurements. It has been found that the flow rate imposed at the inlet of the module has an important effect on the pressure distribution. At the membrane some discrepancies were found between the results obtained with the simulations and with the theoretical approach because of the limitations of the assumptions, especially at low rotating speeds for which the effect of the flow through the module becomes important. The correlations relating the disk rotation rate with the surface averaged pressure and the shear stress on the membrane were determined.