%0 Thesis
%A Renz, Stefanie
%T Methodological Approach Enabling the Two-phase Flow Investigation in Alkaline Electrolysis under Demanding Conditions
%V 661
%I RWTH Aachen University
%V Dissertation
%C Jülich
%M FZJ-2025-02339
%@ 978-3-95806-821-6
%B Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment
%P IX, 252
%D 2025
%Z Dissertation, RWTH Aachen University, 2024
%X In this examination, a methodological approach is developed for the investigation of the two-phase flow behavior of an alkaline electrolysis cell using multiphase particle image velocimetry. Typically, imaging techniques or transparent cells are used to investigate the gas bubble behavior inside electrochemical cells. Certain drawbacks of these methods urge the necessity for a universally applicable two-phase flow investigation method for alkaline electrolysis cells. Therefore, a method is developed which is able to investigate both phases (liquid and gaseous) using a transparent half-cell. The half cell is capable of simulating the alkaline electrolysis two-phase flow behavior on anode or cathode side separately. By exchanging the electrolyte solution for a model electrolyte solution with the same density and viscosity as potassium hydroxide, the two-phase flow investigation can be done at lower temperatures than the usual alkaline electrolysis operation temperature. This is especially advantageous at temperatures above boiling point where pressurized operation is necessary because, with the proposed measurement method, the necessity of operating the electrolysis cell under pressure is avoided. Additionally, the exchange of potassium hydroxide to a less corrosive model electrolyte solution prevents the used transparent cell from getting dull from highly concentrated lye. The simulated cell is operated with equivalent volumes of nitrogen gas instead of hydrogen and oxygen for safety reasons. For method validation, the NeXT (Neutron and X-Ray Tomograph) device at Institute Laue-Langevin (ILL) in Grenoble is used to observe the gas bubbles forming and moving inside the flow channel of an alkaline electrolysis cell. For the first time, a temporal resolution of 0.02 seconds could be achieved for an active cell area of several cm2. Measurement methods like neutron radiography are a powerful tool to analyze the gas bubble behavior inside alkaline electrolysis flow cells, but has limited accessibility. For both measurement methods, neutron radiography measurements and multiphase particle image measurements, cells of the same flowfield geometry are used. For the comparison of both investigation methods, an alkaline water electrolysis single cell is operated at different operation conditions. In this work, the results of both measurement methods are shown and compared. The applicability of an experimentally ”simulated” electrolysis cell, measured with multiphase particle image velocimetry measurements, is shown, as well as the assumptions, prerequisites, and limitations of the simulation of the two-phase flow of an alkaline electrolysis cell. Using the simulated electrolysis half-cell is advantageous compared to neutron radiography measurements because smaller gas bubbles can be identified. Especially for difficult operation conditions like in alkaline electrolysis at intermediate temperatures, where measurements like neutron radiography are extremely difficult to realize, a flow behavior analysis method, which is easy to apply, is helpful. Additionally, the flow behavior of electrochemical flow cells can be optimized for improved electrolysis cell designs and higher efficiencies. This examination is the first step towards a simpler investigation of the two-phase flow behavior of electrochemical cells with the application example of a low temperature alkaline electrolysis zero-gap cell, with the potential to extend the method to intermediate temperature alkaline electrolysis or any other electrochemical device that forms gas bubbles.
%F PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
%9 BookDissertation / PhD Thesis
%R 10.34734/FZJ-2025-02339
%U https://juser.fz-juelich.de/record/1041605