| Summary: | 碩士 === 國立交通大學 === 機械工程學系 === 101 === Water transport rate in the proton exchange membrane fuel cell (PEMFC) should be in a specific range to keep a good electric conductivity in the membrane. This thesis develops an in-situ inspection method to detect water transport through the membrane into flow channels by use of a novel acoustic guided wave transducer. Two anti-symmetric interdigitated piezoelectric fiber composite (AE-PFC) transducers used as the guided wave transmitter and receiver were adhered to the back surface of flow field plate. Guided waves propagate over the flow channel area and carry water information from the transmitter to the receiver. The transducer comes with advantages of narrowband, small mass and high acoustic directivity.
In experiment, a carbon paper used as the gas diffusion layer overlays the area of flow channels. The influence of wet carbon paper on the guided acoustic wave was investigated in accordance with changes of the waveform envelop and the peak value of the signal spectrum. The result indicates the water in the carbon paper reduces reflected echoes of the first guided mode and increases the peak amplitude. On the contrary, the amplitude of the second guided mode decreases as it propagates over the wet area of flow channels. Based on the decreasing of amplitude, the water quantity distributed throughout either the ribs or the flow channels can be determined. The sensitivity of detection is 0.03 and 0.3 mV/μl for water on the ribs and in the flow channels. The range of measuring is 20 to 220 μl. The detecting resolution is up to 5 μl.
Furthermore, finite element analysis was used to explore the electric field of AE-PFC in the process of polarization and guided wave propagation in the flow field plate. The numerical results indicate the electric field is nearly parallel to the piezoelectric fibers. The transient analysis shows the forking phenomenon in the guided mode signal spectra might be caused by the varying adhesive thickness between AE-PFC and the host structure.
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