Deformation-assisted antifouling of surfaces
Author(s)Goon, Grace Swee See.
Massachusetts Institute of Technology. Department of Aeronautics and Astronautics.
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Fouling of surfaces occurs across many scales and applications, ranging from biomedical devices to ships, from membrane separation processes to ice formation on the wings of planes Chemical cleaning of the surfaces is often seen as the de facto treatment, but the drawbacks include the costs of using chemicals, environmental impact and long duration required for the reaction of the chemicals with the foulant With the increased focus on sustainable industrial practices, there has been increased interest in chemical-free options The current state of the art chemical-free antifouling technique employed includes passive methods such as surface treatment or modification, the application of new surface materials, surface vibration, large deformation or heating (for deicing only) The problem of fouling is especially severe in the case of membrane processes due to the variety of foulant types that comes in contact with the membrane surface, the limitation, and complexity of commercially available spiral wound module Recent research work in chemical-free membranes antifouling strategies have likewise focused on surface chemistry, the vibration of magnetically and electrically responsive membranes, the vibration of the entire system and osmotically induced backwashing While surface chemistry reduces the fouling propensity, the system will foul eventually and will still have to be cleaned periodically Osmotically induced backwashing was also found to be severely ineffective in the presence of feed spacers, a feature necessary in the spiral wound module Vibratory methods often require the magnetically or electrically responsive membranes or mechanical assemblage to move the entire system, all of which have drawbacks of their own Firstly, in this thesis, the concept of cyclic deformation is first introduced and its effect studied in a no-flow model cell The membrane is first fouled by creating a layer of uniform alginate gel with known thickness before being placed in a no-flow model cell Deformation is induced by volumetrically controlling the volume of water on one side of the membrane using a syringe pump The interfacial shear strength was then measured after the desired number of cycles It will be shown that the interfacial shear strength decrease with the number of deformation cycles, even though the interfacial shear stresses generated by the cyclic deformation is low This is an indication of interfacial fatigue behavior To understand the eventual failure mechanics, the deformations required to generate sufficient shear stress and strain energy release rate were evaluated A characteristic adhered foulant layer size where the mechanics switches from a strength-based to energy-based mechanics was derived Then, the complexity of the model is increased through the addition of feed pressure, osmotic pressure, permeate flow, and crossflow Over time, alginate and calcium ion near the surface of the membrane will crosslink and form a foulant film that results in flux decline At the desired flux, deformation-induced cleaning (DIC) was applied The membranes were deformed through permeate pressure modulation Excellent flux recoveries were achieved even in the presence of spacers, without incurring any damage to the membrane In contrast, chemical cleaning took 6 times longer than DIC to achieve comparable cleaning performance, while osmotically induced cleaning was completely ineffective in the presence of spacers Finally, DIC was applied to a commercially available spiral wound module and showed flux recoveries over a wide spectrum of feedwater with different fouling propensity To sum up the implication of DIC to real industrial practices, a system analysis was conducted for a medium-size brackish water desalination plant It was shown that the shorter shutdown time of DIC would prompt operators to conduct cleaning more frequently, improving the lifetime average production of the plant by 5-6%, reducing specific energy consumption by 10% and reducing the cost of cleaning by $0 1/m3 of purified water produced Beyond desalination, membranes are used in many food and industrial processes The invention of DIC has a significant impact on making these processes more productive and sustainable at the same time.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, May, 2020Cataloged from the official PDF of thesis. "Due to the condition of the original material, there are unavoidable flaws in this reproduction. We have made every effort possible to provide you with the best copy available. The images contained in this document are of the best quality available"--Disclaimer page.Includes bibliographical references (pages 164-181).
DepartmentMassachusetts Institute of Technology. Department of Aeronautics and Astronautics
Massachusetts Institute of Technology
Aeronautics and Astronautics.