Computational fluid dynamics simulations of flow and concentration polarization in forward osmosis membrane systems

► A computational fluid dynamics model of a forward osmosis system was developed. ► Analytical theory for internal concentration polarization was used in the model. ► Increased mean cross-flow velocity was shown to increase mass-transfer significantly. ► External concentration polarization was signi...

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Bibliographic Details
Published in:	Journal of membrane science Vol. 379; no. 1; pp. 488 - 495
Main Authors:	Gruber, M.F., Johnson, C.J., Tang, C.Y., Jensen, M.H., Yde, L., Hélix-Nielsen, C.
Format:	Journal Article
Language:	English
Published:	Amsterdam Elsevier B.V 01-09-2011 Elsevier
Subjects:	artificial membranes Brackish brackish water Chemistry Colloidal state and disperse state Computational fluid dynamics (CFD) Desalination Exact sciences and technology External concentration polarization Forward osmosis General and physical chemistry Internal concentration polarization mass transfer Membranes osmosis osmotic pressure Porous materials power generation seawater wastewater treatment Forward osmosis Internal concentration polarization External concentration polarization Desalination Computational fluid dynamics (CFD) Support Theory Osmosis Porous material Modeling Membrane separation Fluid model Separation process Membrane Dynamic model Seawater Fluid dynamics Concentration polarization Brackish water Mass transfer Simulation Asymmetric membrane Flow velocity Waste water purification Osmotic pressure
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Summary:	► A computational fluid dynamics model of a forward osmosis system was developed. ► Analytical theory for internal concentration polarization was used in the model. ► Increased mean cross-flow velocity was shown to increase mass-transfer significantly. ► External concentration polarization was significant at low effective flow velocities. ► Increased slip velocity was shown to decrease external concentration polarization. Forward osmosis is an osmotically driven membrane separation process that relies on the utilization of a large osmotic pressure differential generated across a semi-permeable membrane. In recent years forward osmosis has shown great promise in the areas of wastewater treatment, seawater/brackish water desalination, and power generation. Previous analytical and experimental investigations have demonstrated how characteristics of typical asymmetric membranes, especially a porous support layer, influence the water flux performance in osmotically driven systems. In order to advance the understanding of membrane systems, models that can accurately encapsulate all significant physical processes occurring in the systems are required. The present study demonstrates a computational fluid dynamics (CFD) model capable of simulating forward osmosis systems with asymmetric membranes. The model is inspired by previously published CFD models for pressure-driven systems and the general analytical theory for flux modeling in asymmetric membranes. Simulations reveal a non-negligible external concentration polarization on the porous support, even when accounting for high cross-flow velocity and slip velocity at the porous surface. Results confirm that the common assumption of insignificant external concentration polarization on the porous surface of asymmetric membranes used in current semi-analytical approaches may not be generally valid in realistic systems under certain conditions; specifically in systems without mass-transfer promoting spacers and low cross-flow velocities.
Bibliography:	http://dx.doi.org/10.1016/j.memsci.2011.06.022 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0376-7388 1873-3123
DOI:	10.1016/j.memsci.2011.06.022