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@PHDTHESIS{Stockmeier:856875,
author = {Stockmeier, Felix},
othercontributors = {Wessling, Matthias and Mani, Ali},
title = {{F}low fields in the overlimiting current regime in
electrically-driven membrane processes},
volume = {32 (2022)},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-11194},
series = {Aachener Verfahrenstechnik series - AVT.CVT - Chemical
Process Engineering},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2022},
note = {Druckausgabe: 2022. - Auch veröffentlicht auf dem
Publikationsserver der RWTH Aachen University 2023. -
Schreibfehler im Übersetzungstitel des Dokuments:
Strömingsfelder; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2022},
abstract = {Electroconvection, a hydrodynamic instability which
convectively mixes the ion-depleted diffusion boundary layer
in electrically-driven membrane processes, enables the
operation of such processes beyond a diffusion-limited
current density. When operating at overlimiting current
densities, industrial processes could be designed with
smaller membrane modules and, thus, reduced investment
costs. Still, the energy needed to overcome the
diffusion-limitation as well as concerns regarding water
splitting still stand in the way of their application. Both
hindrances can be reduced by effectively triggering and
tailoring the 3D electroconvective vortex field. However,
the 3D features of electroconvection and their interaction
with membrane surface modifications or spacer hydrodynamics
are lacking experimental quantification. Until now,
experimental studies were limited to 2D measurement
techniques and 3D simulations which are restricted to small
scales due to computational costs.This thesis surpasses this
limitation and presents an experimental method for
quantification of the 3D velocity field of electroconvection
with high temporal and spatial resolution. Using this
method, we quantify the velocity field and its statistics
close to a cation-exchange membrane in a steady or pumped
electrolyte. We further measure its interaction with
modified membrane surfaces and spacer structures.We
conducted these measurements in a newly designed
electrochemical cell using micro particle tracking
velocimetry for 3D velocity reconstruction. The recorded
velocity fields were then used to visualize coherent vortex
structures and reveal changes in the velocity field and its
statistics. During the transition from vortex rolls to
vortex rings with increasing current densities, changes in
the rotational direction, mean square velocity, and temporal
energy spectrum with only little influence on the spatial
spectrum were revealed. Additionally, we investigated the
impact of membrane surface modifications with two types of
microgels varying in zeta potential on the vortex field's
build-up. We discovered that a large difference in zeta
potential between microgel and membrane material offers full
control over the velocity field in terms of structure and
rotational direction. Lastly, we quantified the interaction
of the electroconvective velocity field with spacer-induced
hydrodynamics in a pumped electrolyte. The velocity fields
and their statistics revealed that significant interaction
only appears at Reynolds numbers below one. However,
pilot-scale experiments reported the appearance of
overlimiting currents in such systems. Which is why
measurements on a smaller scale at higher current densities
are expected to provide further insights.This thesis
emphasizes the potential of specifically engineered membrane
surfaces and spacer structures for overcoming the
limitations of electrically driven membrane processes.
Tailored interaction of controlled electroconvection and
spacer hydrodynamics could reduce the energy to overcome
limiting currents in industrial applications to a minimum.},
cin = {416110},
ddc = {620},
cid = {$I:(DE-82)416110_20140620$},
pnm = {ConFluReM - Controlling Fluid Resistances at Membranes
(694946) / SFB 985 B06 - Kontinuierliche Trennung und
Aufkonzentrierung von Mikrogelen (B06) (221475706) / DFG
project 191948804 - SFB 985: Funktionelle Mikrogele und
Mikrogelsysteme (191948804)},
pid = {G:(EU-Grant)694946 / G:(GEPRIS)221475706 /
G:(GEPRIS)191948804},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2022-11194},
url = {https://publications.rwth-aachen.de/record/856875},
}
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