Dean flow-enhanced membrane filtration

Secondary flow is a flow region where the flow velocity and direction are significantly different from the primary flow region. The secondary flow could be generated by curved channel, coiled tubes, and rotating movement. The secondary flow generated close to the membrane surface can reduce the concentration polarization and enhance membrane filtration. This section discnsses the secondary flows, including Dean vortices, Taylor flow, and helical membrane modules for the membrane performance enhancement. 

Experimental evidence has demonstrated that Dean vortices can be effective for enhancement of membrane performance under laminar conditions [18]. As flow conditions approach the transition and turbulent flow regimes, straight membranes have a better mass transfer and higher wall shear rate than in flows with curved membrane channels. The effects of Dean vortices on the performance of membrane filtration have been studied experimentally and theoretically by Belfort and coworkers [19-22]. Mallubhotla and Belfort [21] assessed the filtration of suspensions of polydispersed polystyrene particles (mean diameter 25 pm) and silica particles (mean diameter 20 pm) with and without the presence of Dean flow using an 180° U-bend channel... 

Al-Akoum et al. [82] compared the bubbling. Dean flow, and vibrating-enhanced membrane processes in terms of the shear stress and the permeate fluxes obtained in filtration of yeast suspension. The filtration with two-phase flow was carried out using 15 mm ceramic mono tubular UF (permeability 250 L/m h bar) and MF (permeability 1500 L/m h bar) membranes with TMPs of 100 and 25 kPa for UF and MF, respectively. The yeast concentrations used in the two-phase experiments were 1... 

Al-akoum et al. experimentally and theoretically reported the flux enhancement in three particular systems shear-enhanced filtration with a vibrating membrane module, gas/liquid two-phase flows, and Dean vortices for yeast suspension system. They reported that the permeate flux was found to obey the empirical law J -- Twm (where Twm is the mean wall shear stress. Pa) with 0.43 < n < S7 and K depending on the membrane type and the yeast concentration for a particular system. 

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