Abstract
The time-varying flow field in spacer-filled channels of spiral-wound membrane (SWM) modules is mainly due to the development of fouling layers on the membranes that modify the channel geometry. The present study is part of an approach to tackling this extremely difficult dynamic problem at a small spatial scale, by uncoupling the fluid dynamics and mass transfer from the fouling-layer growth process. Therefore, fluid dynamics and mass transfer are studied for a spacer-filled channel whose geometry is altered by a uniform deposit thickness h. For this purpose, 3D direct numerical simulations are performed employing the “unit cell” approach with periodic boundary conditions. Specific thickness values are considered in the range 2.5–10% of the spacer-filament diameter D as well as other conditions of practical significance. The qualitative characteristics of the altered flow field are found to be very similar to those of the reference geometry with no gap reduction. For a given flow rate, the pressure drop, time-average wall-shear stresses and mass-transfer coefficients significantly increase with increasing thickness h due to reduced channel-gap, as expected. Correlations are obtained, applicable at the “unit cell” scale, of the friction factor f and Sherwood number Sh, which exhibit similar functional dependence of f and Sh on the Reynolds and Schmidt numbers as in the reference no-fouling case. In these correlations the effect of channel-gap reduction is incorporated, permitting predictions in the studied range of fouling-layer thickness (h/D) = 0–0.10. The usefulness of the new results and correlations is discussed in the context of ongoing research toward improved modeling and dynamic simulation of SWM-module operation.
Highlights
The spiral-wound membrane (SWM) module is the dominant element of the reverse osmosis (RO) and nanofiltration (NF) water-treatment plants, which are comprised of pressure vessels, each containing several SWM modules in series
Aiming to develop a sound approximate method to tackle this problem, by un-coupling fouling-layer evolution from the fluid mechanical problem, this study considers the effect of uniformly developing fouling layers on fluid dynamics and mass transfer in spacer-filled channel walls
This study is mainly motivated by the need to simulate the time-varying flow field in spacer-filled desalination membrane channels, caused by the development of fouling layers on the membranes that modify the flow-field geometry and affect the transport phenomena at the membrane surface
Summary
The spiral-wound membrane (SWM) module is the dominant element of the reverse osmosis (RO) and nanofiltration (NF) water-treatment plants, which are comprised of pressure vessels, each containing several SWM modules in series. To address this complicated problem in a systematic manner, researchers have numerically analyzed, first, the flow field and mass transfer in restricted spatial domains of the spacer-filled membrane channels, as summarized in [11] Significant work along these lines has been reported (focusing on small or intermediate spatial scales) aiming to understand the effect of spacer characteristics on flow and mass transfer (e.g., [12,13,14]) in order to optimize the feed-spacer geometry (e.g., [15,16,17]) and to study fouling, including bio-fouling (e.g., [18,19]) phenomena. In the analysis and the reported results and correlations (for pressure drop and mass transfer), an additional parameter (h/D) is introduced, involving the fouling-layer thickness h made dimensionless with the diameter D of spacer filaments, the latter considered to be cylindrical
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
