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Introducing a sigmoid function-based transition model for water transport in membrane distillation
Wei, Zijun
Wei, Zijun
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2025-12-01
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Membrane distillation (MD) is an important separation process that allows the vapor phase of solvent in liquid mixture to pass through a porous and hydrophobic membrane, driven directly by the difference in the partial vapor pressure controlled often by a temperature difference. Compared with conventional distillation approaches, MD requires lower-grade thermal energy input and lower operational pressures in producing highly pure solvent (such as water) with minimized membrane fouling and scaling, ideally for scale-flexible and remote separation. The transport of water vapor across the porous membrane governs the operation and performance for MD process. In this thesis program, a transitional model for flux prediction in direct-air MD was proposed, and its validity was proved $(R^2 = 0.6929)$ through comparative study with other three established models including the Bosanquet model $(R^2 = 0.6854)$. A meaningful modification of the Knudsen diffusion specifically for porous channels also provided noticeable improvements in the prediction quality of its own ($R^2$ increased from 0.5090 to 0.5461) and consequently incorporated in our transitional models ($R^2$ improved by around 0.01 to 0.02). Our transitional model not only performs better but also stands on a more solid theoretical foundation. This study also examined the impact of incorporating the Poiseuille flow model into the MD application, showing the deteriorated correlation in all models studied. The proposed transitional equations improved the flux prediction in direct-air MD, leading to better estimation on yield production and cost analysis in helping the MD module design and commercialization deployment. Furthermore, these findings deepen the understanding of MD transport mechanisms.
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Thesis (M.S.)-- Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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Wichita State University
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