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|Title:||Theory of isobaric pressure exchanger for desalination||Authors:||Mei, Chiang C.
Law, Adrian Wing-Keung
|Issue Date:||2012||Source:||Mei, C. C., Liu, Y.-H., & Law, A. W.-K. (2012). Theory of isobaric pressure exchanger for desalination. Desalination and Water Treatment, 39(1-3), 112-122.||Series/Report no.:||Desalination and water treatment||Abstract:||A theory is developed to predict the time of sustained operation of a rotary pressure exchanger used for energy recovery in seawater reverse osmosis system. Based on past experiments for oscillating pipe flows, it is found that the existing plug flow velocity in the ducts is not high enough to induce turbulence in the wall boundary layer. Modeling the time series of the flow velocity in the inviscid core as a periodic series of rectangular pulses, the structure of the laminar momentum boundary layer is first derived. The mass boundary layer induced by the oscillating velocity is then solved in order to obtain the slow diffusion of the averaged brine concentration along the duct. With the result the effective longitudinal diffusivity (dispersivity) is found explicitly for arbitrary Schmidt number. The dispersivity is found to be small due to the small viscosity and mass diffusivity in the very thin boundary layers, however it is still augmented to hundreds times of the molecular diffusivity. For a range of duct and rotor dimensions and rotor frequencies, the time needed for the mixing zone to spread to the ends of the duct is predicted for large Schmidt number appropriate for salt in water. After transient mixing is over, a certain amount of salt leaks steadily into the fresh seawater reentering the membrane. However the leakage is shown to be small due to the small dispersivity.||URI:||https://hdl.handle.net/10356/98028
|ISSN:||1944-3994||DOI:||10.1080/19443994.2012.669166||Rights:||© 2012 Desalination Publications. This paper was published in Desalination and Water Treatment and is made available as an electronic reprint (preprint) with permission of Desalination Publications. The paper can be found at the following official DOI: [http://dx.doi.org/10.1080/19443994.2012.669166]. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.||Fulltext Permission:||open||Fulltext Availability:||With Fulltext|
|Appears in Collections:||CEE Journal Articles|
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