Acoustic Field Induced by Linear Array Ultrasonic Transducers in Graphite Bipolar Plates for PEM Fuel Cells

• Main Authors: Cheng, Po-Yi, 鄭博毅
• Other Authors: Yin, Ching-Chung
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/09504732001384415474

碩士 === 國立交通大學 === 機械工程學系 === 98 === Water management is an important issue to improve performance of proton-exchange-membrane (PEM) fuel cells. In order to understand the feasibility of monitoring water production in PEM fuel cells using ultrasonic visualization, this thesis numerically studies linear array induced ultrasound propagation in graphite bipolar plates with machined flow channels. The material properties of graphite bipolar flow channels were experimentally characterized. Experimental results indicate that it is nearly an isotropic material. Comparing the ultrasonic signals acquired in different states and areas of graphite bipolar plates, the reflected echoes have significant changes when water appears in flow channels. According to the B-scan signals of graphite bipolar plates using immersion focusing ultrasonic transducer, the distribution of water can be clearly determined. Based on the investigation of the acoustic field induced by single element piezoelectric transducer attached on surface of semi-infinite solids, a linear array ultrasonic transducer was further designed. Both graphite composite and pure graphite are considered as acoustic media under investigation. Single element generated ultrasound in pure graphite has narrow main lobe due to its hexagonal anisotropy. The side lobe produced by acoustic phase interference is relatively small. It results that acoustic directivity of sound beam has smaller divergence angle in pure graphite than graphite composite. Transient analysis for acoustic field induced by linear array ultrasonic transducer in graphite bipolar plate indicates that the water distribution in the flow channels can be successfully discriminated.