- 學位論文
電解液流率與寬高比設計對全釩電池效率影響
The effect of electrolyte flow rate and aspect ratio on the efficiency of all-vanadium redox flow batteries
摘要
全釩氧化還原液流電池(VRBS)是一種使用釩離子儲存能量的能源儲存裝置。可與再生能源系統結合進行穩定的電力輸出。由於釩離子濃度在電化學反應下會隨流動方向而變化，且反應區出口附近的濃度過電位在低電解質流率下會有增大的趨勢。透過增加電解質的流率或流速雖可有助於降低濃度過電位，本研究使用改變反應區寬高比的方式來改變電解液的流速，但隨著流增加，其電池內部的壓降也相對增大，導致循環泵增加了額外的功率消耗以及降低系統的淨功率輸出。 本研究中數學模型的開發是為了探討反應區寬高比對電池性能的影響，此外，電解質內質量傳輸過電位的變化也被加進數學模型中，並同時針對局部電流密度與沿著流道的電解質濃度分佈進行探討，循環泵的消耗會根據其電池運作時產生的壓降與電解液流率來計算，並求出電池運作時的淨輸出功率。 結果顯示，電解液流率相同的情況下，寬度窄且高度較高的電池尺寸可提高電池性能，但在高流率時，其電池內部的壓力也相對提升，循環泵的耗功也隨著壓力增大，此數學模型可在設計電池反應區時提供一個指標，並可預測VRB系統的操作狀態。
並列摘要
All-vanadium redox flow batteries (VRBS) are energy storage devices using vanadium ions to store energy. They are combined with renewable energy systems to stabilize power output. During electrochemical reaction the concentration of reactive vanadium varies along flow direction. A small electrolyte flow rate increases the concentration overpotential near the outlet of active area. The concentration overpotential can be reduced by increasing electrolyte flow velocity or flow rate. The flow velocity. Increases with decreasing aspect ratio of reaction area; however, pressure drop is also increased, resulting in increasing power consumption of pumps and lowering net power output. In this study a mathematical model was developed to investigate the effect of aspect ratio of the active area on battery performance. In addition, the mass transport overpotential due to variation of electrolyte concentration was coupled in the model. The distributions of local current density and electrolyte concentration along flow channel were presented and discussed. Power consumption of pumps was determined according to pressure drop and electrolyte flow rate and used to calculate the net power output of a VRB. Modeling results showed that although a low aspect ratio of reaction area increased battery performance due to high electrolyte flow velocity, the power consumption of pumps also increased due to high pressure drop. This model helps design the active area and determine the operating condition of a VRB system.