CFD Modelling of Reverse Osmosis Channels with Potential Applications to the Desalination Industry

Desalination by reverse osmosis is receiving increasing attention due to recent improvements in membrane technology in particular. This technique is now used for small to very large scale applications, and has been identified as a key contributor to water treatment and provision not only in Middle Eastern countries but also closer to home in the United Kingdom for example. Computational Fluid Dynamics (CFD) is increasingly used for complex modelling applications in the chemical process and water industries. Previous work by the writers and others for spacerfilled desalination channels have yielded very good results in terms of modelling the flow and salt characteristics and history in the channels, as well as the overall performance of the membrane system. However, transient features imply that such simulations can be very costly and, if they can approximate experimental layouts with horizontal membranes, the investigation of a full desalination performance and operation remains a very distant prospect. CFD would therefore appear to be unsuited to industrial design at the present time. It is necessary to reduce the cost of the numerical simulations whilst maintaining high fidelity in key design parameters such as pressure loss, shear stress and salt concentration on the membrane, and through flow across the membrane for the method to be useful in design. A momentum loss approach based on a porous medium model is presented to this effect and benchmarked against detailed CFD results with success. It is shown to be capable of meeting key design parameters at a fraction of the full CFD cost.