In this thesis heterogeneous bipolar plates are applied to pure hydrogen PEMFC (called HFC) stacks. The experimental methods are adopted to study the performance and characteristics of the cell under certain operational conditions. In order to obtain the permeability of carbon fiber bipolar plates the pressure drops and flow rates are measured on the two sides of the carbon fiber bunch. A test device has been developed to separate the gas of the two sides so that the gas can only flow through the gaps between carbon fibers. Additionally, the gas pressures on the flow channel and the output voltage of each cell in several locations are measured to help us to understand their relationships. The flow characteristics of the gas reactants in these carbon fiber bipolar plates can also be understood from these measurements.
A bipolar plate with the parallel or serpentine flow channel can be formed by properly arranging the carbon fiber bunches. However, if the oxidizer is air and only single inlet and outlet in cathode chamber are designed, the oxidizer can always not be supplied sufficiently in high power density. The experimental studies display that the output voltages of cells in the midstream or downstream are far below the output voltage in the upstream. The voltage of cells in the upstream is the highest, the next one is in the downstream, and the lowest one is located in the midstream due to accumulating of nitrogen. The insufficiency of oxidizer occurs more seriously in the parallel flow channel than that in serpentine flow channel in single inlet and outlet design. The distribution of current is not uniform especially near midstream, although this phenomenon can be improved by increasing the air inlet pressure. However, the problems are hard to solve in large MEA if we just increase the inlet pressure. Another strategy is needed to solve this problem.
In order to solve the insufficient supply of air in single inlet and outlet design, multiple inlets and outlets are designed. In this design multiple entries can supply enough fresh air driven by fan, and multiple exits can exhaust inert gas by exhausting fan to avoid accumulating in a reactive chamber so that the performance of stack can be improved dramatically.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0824106-120253 |
| Date | 24 August 2006 |
| Creators | Hsiao, Wei-Ming |
| Contributors | none, none, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0824106-120253 |
| Rights | not_available, Copyright information available at source archive |
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