Flux enhancement using oscillatory motion and turbulence promoters

• Published in: Journal of membrane science 2011-09, Vol.381 (1), p.64-73
• Main Authors: Gomaa, H.G., Rao, S., Taweel, M.Al
• Format: Article
• Language: English
• Subjects: adverse effects; artificial membranes; bakers yeast; Chemistry; Colloidal state and disperse state; Exact sciences and technology; Flux enhancement; General and physical chemistry; Membrane separation; Membranes; Microfiltration; mixing; Oscillatory motion; Process intensification; Saccharomyces cerevisiae; Turbulence promoters; turbulent flow
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2011.07.014

► Investigated the effect of oscillation and turbulence promoters on microfiltration. ► For low frequencies, the effect of turbulence promoters (TP) was negligible. ► The flux increased with oscillation frequency, but decreased with its amplitude. ► Close to 10 times increase in flux was achieved compared to no oscillation. Intensification of membrane microfiltration of 3 g/L bakers yeast suspension at 22 °C has been accomplished using 0.22 μm cut-off membranes equipped with transverse edged brass strips turbulence promoters (1.5 mm × 1.5 mm and 15–60 mm spacing) and oscillating at moderate frequencies (0–25 Hz) and small amplitudes (1.5–15 mm) while maintaining constant transmembrane pressure (20–60 kPa) using feedback control scheme. The combined effect of oscillations and turbulence promoters (TP) has proven effective in enhancing the microfiltration flux by an almost order of magnitude over that for a non oscillatory flat surface membranes, and close to four times higher than that achieved in absence of TP under the same oscillation conditions. At low frequencies, the quasi-steady state (QSS) flux behaved in an almost identical manner to that for membranes without TP, where the flux increased mainly due to the cake thinning effect caused by the oscillatory shear. For higher frequencies ( f > 5 Hz), the effect of TP extended further away from the surface resulting in well mixed flow structure which dominated the entire velocity profile during most of the oscillation cycle. Under such conditions, cake removal was mainly due to the mixing and scouring of the surface between the promoters caused by vortices shedding. Such effect was found to increase with oscillations frequency, but decreased with its amplitude. The negative effect of the latter is likely attributed to the length scale of the formed vortices compared to the promoters spacing, which may have resulted in less cake removal and lower filtration flux. Correlation of the quasi-steady state flux was developed which fit the experimental results satisfactorily with R 2 = 0.97.