| DC 欄位 |
值 |
語言 |
| DC.contributor | 機械工程學系 | zh_TW |
| DC.creator | 黃家明 | zh_TW |
| DC.creator | Chia Ming | en_US |
| dc.date.accessioned | 2010-1-28T07:39:07Z | |
| dc.date.available | 2010-1-28T07:39:07Z | |
| dc.date.issued | 2010 | |
| dc.identifier.uri | http://ir.lib.ncu.edu.tw:88/thesis/view_etd.asp?URN=93343037 | |
| dc.contributor.department | 機械工程學系 | zh_TW |
| DC.description | 國立中央大學 | zh_TW |
| DC.description | National Central University | en_US |
| dc.description.abstract | 本論文針對平板式固態氧化物燃料電池(SOFC)的流場板以及陽極微結構進行優化設計，並研究流場不均勻與多孔電極內部流阻所造成的劣化機制。第一個研究目標是分別以數值模擬和實驗量測，研究流場均勻度效應對電池性能的影響。前者採用CFD-RC軟體建立多種不同流場板設計的三維單電池堆數值模式，並以本實驗室顏正和(2004)量測的速度場，驗證數值模式的冷流場。驗證過的數值模式進一步加入反應流場的模組，並模擬採用不同流場板設計的單電池堆性能。結果顯示在雙進口/單出口流場板的進口區加裝導流條，能有效改善流場均勻度，並提升單電池堆的峰值功率密度(PPD)達11%。實驗方面，本研究建立一套可量測SOFC電池性能與交流阻抗的實驗平台，以測試不同流場板設計的單電池堆性能。實驗結果顯示，改善流場均勻度可讓單電池堆的功率輸出被提升13%以上，而由阻抗頻譜分析的結果得知，均勻的流場分佈可分別改善歐姆阻抗與代表氫擴散與轉換的低頻阻抗頻譜達32%與40%，說明了電池性能被改善的原因。
本研究的第二個目標，是以數值模擬研究陽極孔隙率、滲透率以及孔隙撓曲度對電池性能的影響。我們首先量測多孔介質傳輸參數，含用來預測多孔介質流場的Brinkman equation中，常被假設為與流體黏滯係數等值的有效黏滯係數。結果發現，過去文獻常用的假設條件:有效黏滯係數/流體黏滯係數 = 1需做修改，因為有效黏滯係數比流體黏滯係數小了數個數量級(orders of magnitude)。而採用不適當的有效黏滯係數值，可能使數值計算的PPD值產生約10%的誤差。此外，模擬結果說明了三個重點：(1)當孔隙度介於0.2 ~ 0.6，且固定滲透率與孔隙撓曲度，則孔隙度 = 0.3時可獲得最大的峰值功率密度與三相邊界長度；(2) 受限於陽極端的擴散極限，當滲透率 ≤ 10-11 m2時，電池性能隨k值增加的趨勢將趨緩；(3)當孔隙撓曲度 > 1.5時，則孔隙撓曲度值的增加會導致多孔電極內的反應物與生成物更不易進行交換，造成電池性能下降。因此，本文建議可提升陽極支撐SOFC性能的陽極優化微結構為孔隙度 = 0.3, 滲透率 = 10-11 m2, 孔隙撓曲度 = 1.5。本研究所獲得的研究結果，應對於提升SOFC的電池性能以及延長其壽命有所助益。
| zh_TW |
| dc.description.abstract | This thesis aims to study two facets of the polarization problems in planar solid oxide fuel cells (SOFC) concerning optimization of both flow distributors and anodic microstructures with an emphasis on the degradation mechanisms due to effects of flow uniformity in flow channels and flow resistances in porous electrodes. The first objective is to investigate the effect of flow uniformity in various flow distributors to the cell performance of planar SOFC using both numerical simulations and experimental measurements. The former involves several 3-D numerical models implemented by CFD-RC packages which have been used to simulate various hydraulic rib-channel experiments previously performed by Yen (2004) in our laboratory. Numerical flow data were found in good agreement with the experimental results obtained by Yen (2004). Then the validated numerical models were used to evaluate the effect of flow uniformity modulating by various different designs of flow distributors to the cell performance of a single-cell stack. It was found that a new design, using simple small guide vanes equally-spaced around the feed header of the double-inlet/single-outlet module, can effectively improve the degree of flow uniformity in flow distributors resulting in 11% increase of the peak power density (PPD). For experimental measurements, a test rig was established, so that the power-generating characteristics as well as the ac impedance spectra of the single-cell stack using different designs of flow distributors can be measured. The goal is to show how exactly the cell performance would vary with a change in the degree of flow uniformity in these aforementioned flow distributors. We found that by improving the degree of flow uniformity in flow distributors, values of PPD of the single-cell stack can be indeed increased up to 14%. Furthermore, we also found that the ohmic resistance and the low-frequency arc of the single-cell stack can be reduced respectively 32% and 40% when using the optimal flow distributors and the operating voltage is set at 0.6 V.
The second objective is to investigate effects of porosity (e), permeability (k) and tortuosity (t) of anodic microstructures to the cell performance of a single-unit planar anode-supported SOFC using 3-D electrochemical flow models with measured porous transport properties. In particular, we measured an effective viscosity (mu_e) in the Brinkman equation commonly used to predict flow properties in porous electrodes of SOFC. It is found that, contrary to the popular scenario, mu_e is not equal to the fluid viscosity (mu_f), but it is several orders in magnitude smaller than mu_f. This difference can result in more than 10% difference on values of PPD. Our numerical analyses reveal three points. (1) While keeping k and ? fixed with e varying from 0.2 to 0.6, the highest PPD occurs at e = 0.3 where the corresponding triple-phase-boundary length is a maximum. (2) The value of PPD increases slightly with k when k ≤ 10-11 m2 because of the diffusion limitation in anode. (3) The value of PPD decreases with t when t > 1.5 due to the accumulation of non-depleted products. Hence, a combination of e = 0.3, k = 10-11 m2, and t = 1.5 is suggested for achieving higher cell performance of planar SOFC. These results should be useful for further improving cell performance and longevity of planar SOFCs.
| en_US |
| DC.subject | 數值模擬 | zh_TW |
| DC.subject | 流場均勻度 | zh_TW |
| DC.subject | 陽極微結構 | zh_TW |
| DC.subject | 單電池堆測試 | zh_TW |
| DC.subject | 固態氧化物燃料電池 | zh_TW |
| DC.subject | numerical simulations | en_US |
| DC.subject | anodic microstructures | en_US |
| DC.subject | flow uniformity | en_US |
| DC.subject | cell tests | en_US |
| DC.subject | solid oxide fuel cell | en_US |
| DC.title | 平板式固態氧化物燃料電池流場板與陽極微結構之優化設計與實作測試 | zh_TW |
| dc.language.iso | zh-TW | zh-TW |
| DC.title | Optimizations of Flow Distributors and Anodic Microstructures for Planar SOFC | en_US |
| DC.type | 博碩士論文 | zh_TW |
| DC.type | thesis | en_US |
| DC.publisher | National Central University | en_US |