Braun K (2026)
Publication Type: Thesis
Publication year: 2026
URI: https://open.fau.de/handle/openfau/39266
The aim of this thesis is to present a methodology for the thermodynamic evaluation of electrochemical energy systems. The necessary theoretical considerations and their poten tial, as well as the requirements for measurement and test bench technology in experimen tal investigations, are presented. Based on the definition of efficiencies, a possible method for evaluating the systems is demonstrated. The influence of changes in the parameters of stoichiometry, pressure, and carrier sub stances on the entire system is demonstrated. These relationships are usually complex and therefore require a thorough system analysis. For this purpose, the systems are considered as quasi-stationary systems. Energy and exergy balancing according to the first and second law of thermodynamics are described as useful tools. The balancing is carried out in previously defined balancing areas, which can be defi ned at the component, subsystem, or overall system level, depending on the area of in terest. Using so-called 0D models, which are averaged over location and are partially time-independent, all energy-carrying substances can be analyzed and an efficient system architecture can be identified. By defining various boundary conditions, scenario analyses can be performed and efficient system configurations can be determined. Experimental data is particularly necessary for application-oriented evaluation. The thesis shows how energy balancing can be implemented experimentally using the example of a fuel cell. The focus is on the parameter relative humidity, which is relevant due to the necessary water management in PEM fuel cells. It can be shown that even small measure ment deviations have an influence on the system design, in this example on the design of the cooling system. A gas sensor based on Raman scattering is presented as an alternative to the commonly used capacitive humidity sensors. This allows to determine the partial pressure of water vapor directly, whereas a capacitive sensor requires several conversion steps in between. In addition to recording the thermodynamic parameters, it is important to reliably set the operating conditions in order to generate measurement data that can be used in an overall system simulation. This thesis compares two different humidificati on concepts– a bubble humidifier and direct evaporation. The fundamental difference in setting the target parameter is highlighted. Compared to bubble humidifiers, direct evapo ration provides the advantage of accurately determining the amount of evaporated water. This results in precise adjustment of the relative humidity at the fuel cell inlet. The test bench „AxCELL“ was set up to determine the complete energy balance of the cell. As part of the balancing process, this thesis explains how the water balance is mea sured. The third part of this thesis aims to demonstrate the actual efficiency assessment. Exergy efficiency and a defined reversible efficiency prove to be suitable assessment parameters. Although exergy efficiency can be used for comparison purposes, its informative value with regard to efficiency is limited. Reversible efficiency, which has the actually measured useful work as its primary target variable, indicates how far a process is from its ideal in terms of energy conversion. It thus provides a useful reference point in the development of new electrochemical processes. Finally, an efficiency analysis is performed using the example of the system application of electrochemical dehydrogenation with a hydrogen fuel cell.
APA:
Braun, K. (2026). Thermodynamische Bewertung von elektrochemischen Energiesystemen (Dissertation).
MLA:
Braun, Katharina. Thermodynamische Bewertung von elektrochemischen Energiesystemen. Dissertation, 2026.
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