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Open AccessArticle

Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics

1
UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, University of New South Wales (UNSW), Sydney, NSW 2052, Australia
2
Eurecat, Centre Tecnològic de Catalunya, Water, Air and Soil Unit, 08005 Manresa, Spain
3
Institut Européen des Membranes, UMR5635, 34090 Montpellier, France
*
Author to whom correspondence should be addressed.
Membranes 2020, 10(5), 111; https://doi.org/10.3390/membranes10050111
Received: 10 May 2020 / Revised: 22 May 2020 / Accepted: 23 May 2020 / Published: 25 May 2020
(This article belongs to the Special Issue Selected Papers from the MSA ECR & IMSTEC 2020)
In an effort to improve performances of forward osmosis (FO) systems, several innovative draw spacers have been proposed. However, the small pressure generally applied on the feed side of the process is expected to result in the membrane bending towards the draw side, and in the gradual occlusion of the channel. This phenomenon potentially presents detrimental effects on process performance, including pressure drop and external concentration polarization (ECP) in the draw channel. A flat sheet FO system with a dot-spacer draw channel geometry was characterized to determine the degree of draw channel occlusion resulting from feed pressurization, and the resulting implications on flow performance. First, tensile testing was performed on the FO membrane to derive a Young’s modulus, used to assess the membrane stretching, and the resulting draw channel characteristics under a range of moderate feed pressures. Membrane apex reached up to 67% of the membrane channel height when transmembrane pressure (TMP) of 1.4 bar was applied. The new FO channels considerations were then processed by computational fluid dynamics model (computational fluid dynamics (CFD) by ANSYS Fluent v19.1) and validated against previously obtained experimental data. Further simulations were conducted to better assess velocity profiles, Reynolds number and shear rate. Reynolds number on the membrane surface (draw side) increased by 20% and shear rate increased by 90% when occlusion changed from 0 to 70%, impacting concentration polarisation (CP) on the membrane surface and therefore FO performance. This paper shows that FO draw channel occlusion is expected to have a significant impact on fluid hydrodynamics when the membrane is not appropriately supported in the draw side. View Full-Text
Keywords: forward osmosis; computational fluid dynamics (CFD); spacers; draw channel; pressure assisted osmosis forward osmosis; computational fluid dynamics (CFD); spacers; draw channel; pressure assisted osmosis
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MDPI and ACS Style

Charlton, A.J.; Lian, B.; Blandin, G.; Leslie, G.; Le-Clech, P. Impact of FO Operating Pressure and Membrane Tensile Strength on Draw-Channel Geometry and Resulting Hydrodynamics. Membranes 2020, 10, 111.

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