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%0 Thesis %A Görtz, Jonas Tim %T Experimental and model-based study of gas-liquid-solid flows in pH-shift electrolyzers %V 17 %I Rheinisch-Westfälische Technische Hochschule Aachen %V Dissertation %C Aachen %M RWTH-2025-07292 %B Aachener Verfahrenstechnik - Fluidverfahrenstechnik - Dissertationen %P 1 Online-Ressource : Illustrationen %D 2025 %Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University %Z Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2025 %X In the context of the circular economy, electrochemical pH shift techniques offer a promising alternative to conventional pH management methods that rely on additives. The transition away from fossil carbon sources leads to pH management playing a central role in processes such as biotechnological production and recycling processes for carboxylic acids, as aqueous streams require processing. The properties of the different acid species, which depend on the pH value, are specifically utilized to enable their separation. For example, electrochemical crystallization takes advantage of the lower solubility of the fully protonated acid species to perform reactive pH shift crystallization. This work presents a detailed study of fluid dynamics in electrochemical separation units. For this purpose, the size and velocity of electrolytically generated oxygen and hydrogen gas bubbles and the spatially resolved, qualitative flow of the electrolyte are measured experimentally. For this purpose, a specially developed semi-transparent electrolyzer is used, which provides new insights into the gas-liquid flow. Next, based on the state of the art, a new Euler-Lagrangian model for the simulation of the fluid dynamics of the gas-liquid flow is proposed, which depicts the expansion of the gas bubble curtain through bubble-bubble collisions. For this implemented model, suitable parameters, e.g., grid size, drag coefficient, and collision model, are selected through a sensitivity study. These simulation parameters are then used to simulate the novel electrolysis apparatus, and the model is validated with experimental data. Finally, the model can be used to analyze a new prototype for the electrochemical crystallization of carboxylic acids. Here, the influence of different current densities and electrolyte volume flows on the flow profile and spatial distribution of the gas bubbles can be investigated. Furthermore, the acid species concentration, pH, and supersaturation profiles can be determined by simulating the anodic and dissociation reactions. This model-based analysis enables the identification of dead zones and the study of different electrode-membrane gaps, quantifying their influence on the maximum local supersaturation. In the future, the model-based analysis established in this work enables the evaluation and development of new prototype designs for electrochemical crystallization. %F PUB:(DE-HGF)11 ; PUB:(DE-HGF)3 %9 Dissertation / PhD ThesisBook %R 10.18154/RWTH-2025-07292 %U https://publications.rwth-aachen.de/record/1017302