Fuel Cell Symposium
Utrecht
2012-06-04
Chair: D. Kehrwald (Adam Opel AG)
Program:
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------09.00 am – 09.05 am : Welcome
S.M. Hassanizadeh (Univ. Utrecht)
09.05 am – 09.45 am : Current and Future Challenges in PEM FC Modeling
D. Rensink (Adam Opel AG)
09.45 am – 10.25 am : Two-Phase Flow Modeling in a PEM FC
C. Qin (Univ. Utrecht/Adam Opel AG)
10.25 am – 10.40 am : Coffee Break
10.40 am – 11.20 am : Coupling Two-Phase Compositional Porous Medium and Free Flow
K. Baber (Univ. Utrecht)
11.20 am – Noon
R. Helmig (Univ. Stuttgart)
: Modeling the Water Management in PEM FCs
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Noon – 01.00 pm
: Lunch break
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------01.00 pm – 01.35 pm : From Morphogenesis to Fluid Flow - Fields of Application for SPH at ICVT
U. Nieken (Univ. Stuttgart)
01.35 pm – 02.10 pm : Mobility and Distribution of Phosphoric Acid in HT PEM FCs
W. Lehnert (FZ Jülich)
02.10 pm – 02.45 pm : Dependency of Wetting Dynamics on Initial Hydraulic Conditions
V. Joeker-Niasar (Univ. Utrecht)
02.45 pm – 03.00 pm : Closing Remarks
D. Rensink (Adam Opel AG)
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Abbreviations:
HT PEM FC - High Temperature Polymer Electrolyte Membrane Fuel Cell
ICVT
- Institut für Chemische Verfahrenstechnik (Institut for Chemical Process Engineering)
PEM FC
- Polymer Electrolyte Membrane Fuel Cell
SPH
- Smoothed Particle Hydrodynamics
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Abstracts
D. Rensink: Current and Future Challenges in PEM FC Modeling
In this presentation we summarize the state-of-the-art of polymer electrolyte membrane (PEM) fuel cell
modeling. Currently superfast 1+1D models and CFD based comprehensive 3D models are widely used
for cell level modeling with various objectives. Both model types are based on macroscopic constitutive
relations to describe the transport processes in the various layers and the electrochemistry. Often
microscopic models serve as a base to derive the relations alongside with experimental results. One of the
current challenges in fuel cell modeling is the description of liquid water flow in the porous layers. Here
Darcy's law is widely used. However, there is experimental evidence that the validity of Darcy's law is
only limited in thin materials like gas diffusion layers and that some modifications need to be done.
Another challenge is the description of liquid water flow in the reactant channels in the framework of an
unified water transport model which is best suitable for numerical modeling. The development and
validation of these models require dedicated and specifically designed experiments which focus on one
aspect. Exemplarily, a micro fuel cell will be presented which allows for being used in synchrotron
radiation topographical imaging experiments by fully exposing the entire active area to the beam and as
well as being represented fully in numerical simulation without blowing up memory and CPU
requirements. Imaging data of such a micro fuel cell, for instance, providing liquid water distributions and
movement offer valuable validation data for two-phase models.
Future challenges comprise the extension of the current models to the stack level as well as the reduction
of model parameters by a smart combination of microscopic and macroscopic models. The
comprehensive model itself may need refinement, e.g. regarding the membrane water transport
mechanisms or the catalyst layer model. Furthermore, the parameterization of the comprehensive models
is a challenge on its own.
C. Qin: Two-Phase Flow Modeling in a PEM FC
Numerical modeling plays an important role in understanding various transport processes in polymer
electrolyte fuel cells (PEFCs). It can not only provide insights into the development of new PEFC
architectures, but also optimize operating conditions for better cell performance. Water balance is critical
to the operation of PEFCs, since the membrane needs to attain sufficient water for effective ionic
conduction. On the other hand, too much water accumulating in PEFCs would result in mass transport
limitations, which is termed as liquid water flooding. In most cases, liquid water flooding occurs in
porous diffusion layers and micro gas channels at the same time. This can limit the cell performance and
detract the durability of PEFCs. In this talk, I would present the frontiers of numerical modeling of
PEFCs with a focus on gas-liquid two-phase transport. In addition, current challenges in numerical
modeling of PEFCs will be pointed out, such as validation of two-phase Darcy’s law in gas diffusion
layer and interface treatments between adjacent layers (e.g. the interface treatment between gas channel
and gas diffusion layer). It also needs to be noted that modeling of liquid water dynamics in gas channels
has received much attention due to its importance in water management of PEFCs. Up to now, most
previous works focused on explicit tracking of gas-liquid water interface for providing fundamental
understanding of water dynamics in gas channels. However, a macro gas channel flooding model is more
required for engineering applications due to its computational effectiveness. In this talk, I would give a
detailed discussion on our recently proposed gas channel flooding model (one-dimensional
phenomenological model for liquid water flooding in cathode gas channel of a polymer electrolyte fuel
cell, JES, 2012). At last, I shall outline some future works relating to two-phase flow modeling in PEFCs.
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K. Baber: Coupling Two-Phase Compositional Porous Medium and Free Flow
Flow and transport processes in domains composed of a porous medium and an adjacent free-flow region
appear in a wide range of industrial, environmental and medical applications. In this context, evaporation
is an ubiquitous process, since evaporation rates and patterns affect the energy balance of terrestrial
surfaces and drive an array of climatic processes. Notwithstanding its prominence for many natural and
engineering applications, prediction of evaporative drying rates from porous media remains a challenge
due to complex interactions between the porous medium and the free-flow system, the ambient conditions
(radiation, humidity, temperature, air velocity, turbulent conditions) at the interface, and the internal
porous-medium properties that lead to abrupt transitions and rich flux dynamics.
The numerical simulation of flow and transport phenomena in porous media is quite often based on
Darcy's law, whereas in free flow regions the (Navier-)Stokes model has to be used. Of special interest
are structures composed of a porous part and an adjacent free flowing fluid. So far, the coupling of free
flow with porous medium flow has been considered only for a single-phase system. We extend this
classical concept to two-component non-isothermal flow with two phases inside the porous medium and a
single phase inside the free flow region. Our coupling concept also takes into account evaporation and
condensation processes at the interface. We discuss our new model and introduce different coupling
conditions. Moreover, some numerical examples illustrate the coupling between the two model domains.
R. Helmig: Modeling the water management in PEM FCs
The development of alternative power sources/supplies is an important task nowadays. Polymer
electrolyte membrane (PEM) fuel-cells currently are intensively investigated and improved for
applications. This requires a profound understanding of the physical and electrochemical processes
occurring in fuel cells. It has been found that the kinetics of the oxygen reduction at the cathode is a
limiting factor for the performance of fuel-cells. The transport of oxygen to the cathode through its
porous diffusion layer takes place in a predominantly diffusive manner. The generation of liquid water at
the cathode-site limits this oxygen transport to the reaction layer. A crucial issue here is the wettability of
the porous media. The material might consist, for example, of a carbon fiber structure hydrophobized
with Teflon. Hydrophobic properties enhance the removal of the generated liquid water. However, it has
been observed that, under operating conditions, at least parts of the diffusion layer become hydrophilic
and retain liquid water in high residual saturations. Thus, an efficient water management in the cathode
diffusion layer is necessary to improve the performance of the fuel cell. Multiphase multicomponent
models originally developed at our working group for the simulation of non-isothermal multiphase
processes in the subsurface are applied for modeling the diffusion layer of PEM fuel-cells. However, this
is in an early stage. So far we have simulated processes occurring in the diffusive layer. Further research
is necessary e.g. to understand the complex wettability behavior.
The aim of this presentation is to discuss the physical and numerical model concept, the assumptions that
are necessary and with numerical results the possibilities and restrictions.
U. Nieken: From Morphogenesis to Fluid Flow - Fields of Application for SPH at ICVT
Porous materials are widely used in chemical engineering. The efficiency of each process is significantly
dependent on the structure and the physical properties of the porous media. From our point of view there
are two principal challenges - first, not only, but commonly known: the transport properties of the porous
media - and second, often missed: the description of the process which generates porous media!
In this presentation we show different applications of SPH from our research group "physico-chemical
process engineering". In general we consider systems of multiple phases with chemical reactions and
phase transitions where evolving interfaces and moving contact lines play an important role. In this way
we like to give you an impression about porous materials research in chemical process engineering.
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W. Lehnert: Mobility and Distribution of Phosphoric Acid in HT PEM FCs
In high temperature polymer electrolyte fuel cells (HT-PEFC) the proton conductivity relies on
phosphoric acid doped polybenzimidazole as electrolyte. In our studies we used poly (2,5-benzimidazole)
(ABPBI) provided by the company FuMaTech. We showed that the performance of cells is almost
independent of the way of acid introduction into the membrane-electrode-assembly (MEA) but strongly
depends on the amount inserted into it. The doping of the membrane was done via phosphoric acid
impregnated electrodes with and without pre-doped membranes. The electrodes and the membrane were
assembled in the cell without a previous hot press step. The cells were afterwards operated under standard
conditions. Chemical analysis after shut down revealed that in all these MEAs the phosphoric acid
distribution between the membrane and the electrodes was nearly the same. Furthermore a rapid start-up
of MEAs impregnated with phosphoric acid via the electrodes was possible. These experiments indicate
very fast kinetics of the redistribution of phosphoric acid within the MEA being accelerated by gaseous
product water from the fuel cell operation.
In order to observe the redistribution and hydration/dehydration of phosphoric acid in situ, impedance
measurements and synchrotron X-ray radiography measurements were carried out during operation of
cells at different operating conditions. Differently conditioned cells were investigated during the heatingup. For one cell, a classical 70 h break-in procedure was performed while for the other cell, which was
assembled two hours before starting the experiments, no break-in procedure was carried out. Furthermore,
cells were examined during load changes. The results show that the local distribution of phosphoric acid
in the MEA and the thickness of the membrane are dependent on the operating conditions due to
hydration and dehydration process. Moreover the results allow an estimation of the concentration of the
phosphoric acid in the membrane at the different current densities applied.
The mobility and hydration/dehydration of phosphoric acid in HT-PEFC MEAs was observed in situ with
synchrotron X-ray measurements in combination with impedance spectroscopy.
V. Joeker-Niasar: Dependency of Wetting Dynamics on Initial Hydraulic Conditions
Dynamics of capillary rise in a porous medium has been mostly studied in initially-dry systems. As initial
saturation and initial hydraulic conditions in many natural and industrial porous media can be variable, it
is important to investigate the influence of initial conditions on the dynamics of the process.
In this study, using dynamic pore-network modeling, we simulate capillary rise in a porous medium for
different initial saturations (and consequently initial capillary pressures). Furthermore, the effect of
hydraulic connectivity of the wetting phase in corners on the height and velocity of the wetting front will
be studied. Our simulation results show that there is a trade-off between capillary forces and trapping due
to snap-off, this leads to a nonlinear dependence of wetting front velocity on initial saturation at pore
scale. This analysis may provide a possible answer to the experimental observations in the literature
showing a non-monotonic dependency between initial saturation and the macroscopic front velocity.
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List of Participants
Prof. S.Majid Hassanizadeh
Professor of Environmental Hydrogeology
Department of Earth Sciences
Faculty of Geosciences
Utrecht University
P.O. Box 80021
3508 TA UTRECHT
The Netherlands
Phone: +31 30 2537464
Sec.: +31 30 2535031
Fax: +31 30 2535030
Email: hassanizadeh@geo.uu.nl
Dr.-Ing. Dirk Rensink
Adam Opel AG
GM Alternative Propulsion Center Europe
Advanced Propulsion CAE, CFD and H2 Technology
IPC MK-01
65423 Rüsselsheim
Germany
Phone: +49 6142 7 67616
Fax: +49 6142 7 66152
Email: dirk.rensink@de.opel.com
Dr. rer. nat. Dirk Kehrwald
Adam Opel AG
GM Alternative Propulsion Center Europe
Advanced Propulsion CAE, CFD and H2 Technology
IPC MK-01
65423 Rüsselsheim
Germany
Phone: +49 6142 7 64165
Fax: +49 6142 7 54359
Email: dirk.kehrwald@de.opel.com
Chaozhong Qin
Adam Opel AG
GM Alternative Propulsion Center Europe
Advanced Propulsion CAE, CFD and H2 Technology
IPC MK-01
65423 Rüsselsheim
Germany
Phone: +49 6142 7 60414
Fax: +49 6142 7 66152
Email: chao.zhong.qin@de.opel.com
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Prof. Dr.-Ing. Ulrich Nieken
Universität Stuttgart
Institut für Chemische Verfahrenstechnik
Böblinger Str. 78
70199 Stuttgart
Germany
Phone: +49 711 685 85230
Fax: +49 711 685 85242
Email: ulrich.nieken@icvt.uni-stuttgart.de
Prof. Dr. Werner Lehnert
Institut für Energie- und Klimaforschung (IEK)
Forschungszentrum Jülich GmbH
IEK-3: Brennstoffzellen
52425 Jülich
Germany
Tel: +49 2461 61 3915
Fax: +49 2461 61 6695
E-Mail: w.lehnert@fz-juelich.de
Prof. Dr.-Ing. Rainer Helmig
Universität Stuttgart
Institut für Wasser- und Umweltsystemmodellierung
Pfaffenwaldring 61
70569 Stuttgart
Germany
Tel.: +49 711 685 64741
Fax: +49 711 685 60430
E-Mail: rainer.helmig@iws.uni-stuttgart.de
Katharina Baber
Universität Stuttgart
Institut für Wasser- und Umweltsystemmodellierung
Pfaffenwaldring 61
70569 Stuttgart
Germany
Tel.: +49 711 685 64741
Fax: +49 711 685 60430
E-Mail: iwskbabe@iws.uni-stuttgart.de
Dr. Vahid Joeker-Niasar
Shell Rijswijk
Postbus 60
2280 AB Rijswijk
The Netherlands
Tel.: +31 70 447 3911 (Switchboard)
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