| 摘要: | 本研究建立一套具備三維、穩態、等溫特性的數值模擬模型，以探討流道幾何對低溫質子交換膜燃料電池性能之影響，針對三種不同流道結構進行模擬與分析，分別為傳統矩形流道、漸縮比 0.417 與漸縮比 0.624 的變截面流道設計。模擬操作電壓設定於 0.7 V（中負載）與 0.5 V（高負載）兩種工況，以對應實際燃料電池運作下的不同負載情形。研究內容涵蓋極化曲線分析、反應氣體（氧氣）濃度分佈、水氣濃度分佈、電流密度分佈，以及陰極流道內之氣體速度場。
模擬結果顯示，漸縮比0.624之變截面流道在各項性能指標中表現最為理想。在氧氣傳輸方面，其濃度分佈在流道與氣體擴散層交界面展現優異均勻性，有效覆蓋整個觸媒層反應區域，顯著降低肋條下方之氣體匱乏現象，並減緩濃度極化。電流密度分佈亦呈現廣泛且穩定的高密度區域，反應效率空間利用率高，證實其有助於提升整體電堆輸出功率。同時，在陰極流道速度場方面，漸縮比0.624流道設計可產生良好之速度梯度，不僅增進氣體傳輸，也有助於將產生之水氣帶離觸媒層與氣體擴散層，有效減少積水現象並強化水管理能力。
相對之下，傳統矩形流道因流道寬度與肋條間無變化，導致氣體流動路徑單一且速度集中於中央，缺乏對側邊與下方之供應能力，造成反應物分佈不均與局部電流密度過低的問題。在高負載條件下（0.5 V），更易形成嚴重的水氣堆積與供氧不足，整體效能明顯劣於變截面結構。
整體而言，變截面流道設計可同時優化反應物傳輸與使水分被移除，提升PEMFC在高負載下之操作穩定性與效能表現。其中漸縮比0.624流道為本研究中最佳幾何結構，提供未來燃料電池流場設計實務之重要參考依據。
;This study establishes a three-dimensional, steady-state, isothermal numerical model to investigate the impact of flow channel geometry on the performance of low-temperature proton exchange membrane fuel cells (PEMFCs). Three different flow channel configurations were analyzed: a conventional rectangular channel and two tapered variable cross-section channels with contraction ratios of 0.417 and 0.624. Simulations were conducted under two operating voltages—0.7 V (medium load) and 0.5 V (high load)—to represent different practical fuel cell working conditions. The analysis focuses on polarization behavior, reactant gas (oxygen and hydrogen) concentration distribution, water vapor saturation, current density distribution, and gas velocity fields within the cathode channels.
Simulation results indicate that the tapered channel with a contraction ratio of 0.624 exhibits the best overall performance across all evaluation metrics. For both oxygen and hydrogen transport, this design achieves superior uniformity in concentration distribution along both the XY and YZ planes, ensuring effective coverage of the catalyst layer and significantly reducing local reactant depletion and concentration polarization. The current density distribution is also broader and more stable, indicating high spatial utilization of the reaction zone and improved power output. Moreover, the 0.624 channel geometry generates favorable velocity gradients within the cathode flow field, enhancing reactant transport and effectively assisting in the removal of water vapor from the catalyst layer and gas diffusion layer (GDL), thereby improving water management and mitigating flooding risks.
In contrast, the conventional rectangular channel—with constant width and rib spacing—exhibits a more centralized flow path and limited lateral gas dispersion. This results in uneven reactant supply and low current density beneath the ribs. Under high load conditions (0.5 V), severe water accumulation and oxygen deficiency are observed, leading to significantly reduced performance compared to the tapered designs.
In summary, the variable cross-sectional flow channel design effectively improves both reactant distribution and water removal, thereby enhancing the stability and performance of PEMFCs under high-load operation. Among the tested geometries, the contraction ratio of 0.624 provides the best overall performance and serves as a valuable reference for future practical flow field design in high-performance fuel cell systems. |
