This title appears in the Scientific Report :
2006
Please use the identifier:
http://hdl.handle.net/2128/549 in citations.
Entwicklung und Optimierung von Direktmethanol-Brennstoffzellstapeln
Entwicklung und Optimierung von Direktmethanol-Brennstoffzellstapeln
In the Direct Methanol Fuel Cell (DMFC), methanol is used as a liquid energy source for the production of electric energy. In comparison to hydrogen, the energy density of methanol is much higher. In the present work, different ways of improving the performance of fuel cell stacks will be examined....
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Personal Name(s): | Müller, Martin Johannes (Corresponding author) |
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Contributing Institute: |
Energieverfahrenstechnik; IWV-3 |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2006
|
Physical Description: |
167 S. |
Dissertation Note: |
RWTH Aachen, Diss., 2006 |
ISBN: |
3-89336-434-X |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Rationelle Energieumwandlung |
Series Title: |
Schriften des Forschungszentrums Jülich. Reihe Energietechnik / Energy Technology
51 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
In the Direct Methanol Fuel Cell (DMFC), methanol is used as a liquid energy source for the production of electric energy. In comparison to hydrogen, the energy density of methanol is much higher. In the present work, different ways of improving the performance of fuel cell stacks will be examined. The influence of operating parameters, on the one hand, and design parameters, on the other hand, on the performance of the fuel cell system and the fuel cell stack will be tested. Using measurements of stacks and single cells, important phenomena for the DMFC stack setup will be investigated. This examination will be divided into three parts: the development of characteristic parameters, the assessment of operating parameters and the examination of stack components. Using these results, models, which include parameters that are relevant for stack setup and stack operation, will be developed. Along with the different characteristic parameters used to assess power density, the linear IV characteristic will be introduced as a useful instrument for the optimisation and design of stacks. Understanding mass transport in the membrane electrode assembly (MEA) is of decisive importance for the functioning of cells and stacks. Based on the overall mass flow, calculations of the mass transport will be made for the anode and cathode. In order to describe the diffusive mass transport at the cathode, a diffusion model will be developed and transferred to cathode channel. This will provide information on the distribution of the current density along the flow channel. Furthermore, these calculations and measurements will show that the water drain, in particular, has a significant influence on the current density. On the basis of case studies, the functionality of different stack concepts will be discussed. The flow distribution of woven structures and meander structures will be compared. It will be shown that all structures have a homogeneous flow distribution with one phase flow. However, channel structures with integrated wicks have the best flow distribution at a low pressure drop with multiphase flow. The comparison of the stack concepts will demonstrate that monopolar ones are more suitable for systems with limited space, whereas bipolar stacks are appropriate for more powerful systems. The electrical properties of the cell will be reproduced with a web of resistors. When using large cell areas, it is possible that ohmic losses in the current collector plates could lead to the inhomogeneous distribution of potential and thus cause a loss of power density. A dimensioning tool will be presented, which makes the calculation of stack dimensions according to given boundary conditions possible. By varying the boundary conditions, it can be shown that there is an optimal cell number for a maximum specific stack power density. In order to improve the compact setup of fuel cell systems, the integration of system components into the stack will also be presented. |