Flux enhancement during Dean vortex microfiltration. 8. Further diagnostics1

Application of a Surface-Renewal Model to Permeate-Flux Data for Constantpressure Cross-Flow Microfiltration With Dean Vortices

“…609 -627, April -June, 2015 particulates away from the membrane wall and dramatically enhance permeation rates compared to operation without vortices, although at the expense of a larger axial pressure drop. Flux improvements of up to 43% have been reported by Mallubhotla and Belfort (1997) in CFMF of particulate suspensions, while Gehlert et al (1998) found enhancements of 30−120% for ultrafiltration and microfiltration of relatively low concentrated baker's yeast suspensions and 30-90% for microfiltration of relatively concentrated beer yeast. The flux enhancement was found to increase with feed flow rate and transmembrane pressure drop, and decrease with increasing feed concentration of suspended matter (Mallubhotla and Belfort, 1997).…”

“…In a series of publications, Belfort and co-workers conducted comprehensive theoretical and experimental investigations on the nature of the flow field in curved channels and the effects of the resulting centrifugal instabilities, known as Dean vortices, on the performance of nanofiltration, ultrafiltration and microfiltration membrane modules (Chung et al, 1996;Mallubhotla and Belfort, 1997;Chung et al, 1998;Gehlert et al, 1998;Mallubhotla et al, 1998;Luque et al, 1999;Mallubhotla et al, 1999;Mallubhotla et al, 2001). The central conclusion that can be drawn from this body of work is that such vortices induce back migration of accumulated solute molecules or Brazilian Journal of Chemical Engineering Vol.…”

“…A recently developed surface-renewal model for constant-pressure, cross-flow microfiltration (Hasan et al, 2013) is applied to the permeate-flux data reported by Mallubhotla and Belfort (1997), one set of which included flow instabilities (Dean vortices) while the other set did not. The surfacerenewal model has two forms ─ the complete model and an approximate model.…”

“…For the approximate model, a 50% increase in the value of surface renewal rate is shown due to vortices, which increases the limiting permeate flux by 30%, decreases the specific cake resistance by 10.5% and decreases the limiting cake mass by 13.7%. The cake-filtration version of the critical-flux model of microfiltration (Field et al, 1995) is also compared against the experimental permeate-flux data of Mallubhotla and Belfort (1997). Although this model can represent the data, the quality of its fit is inferior compared to that of the surface-renewal model.…”

Influence of Residence-Time Distribution on a Surface-Renewal Model of Constant-Pressure Cross-Flow Microfiltration

“…Compared to the film and boundarylayer models of membrane filtration, the surfacerenewal model has the potential to more faithfully describe the transfer of dissolved/suspended solids due to random hydrodynamic impulses generated at the membrane surface, e.g., due to membrane roughness or by the use of spacers or turbulence promoters. Such instabilities, when introduced deliberately into the main flow (e.g., by means of Dean vortices), induce back migration of accumulated solute molecules or particulates away from the membrane surface and significantly enhance permeation rates (Mallubhotla and Belfort, 1997;Gehlert et al, 1998;Mallubhotla et al, 1998). Almeida et al (2010) experimentally studied the effect of wall roughness and three different spacer configurations on the microflow hydrodynamics of deionized water flowing in slits for a Reynolds number range of 58−500.…”