Mass Transfer of a Forced Two Phase Flow on Rotating-Disk Electrode

本研究是利用旋轉盤電極(Rotating-Disk Electrode)系統，以強制二相流方式(液-液兩相，其中一相是經由靜態混合攪拌器(Static mixer)而產生液滴狀分散於另一相)，來達到增進質量傳送的目的。質傳速率是藉由量測鐵氰化合物系統(Ferric/Ferrous Cyanide)之還原極限電流(Limiting current)推算得知。藉由改變轉速，有機相之分率和有機相之液滴粒徑大小等因素，探究對連續相反應的質傳影響。並將加入分散相液滴的二相系統之質傳速率和僅有單一連續相之質傳速率相比較，結果確有增強質量傳送的效果。將所得實驗數據以無因次化分析(Dimension alanalysis)方法組合成幾個其有物理意義的無因次參數，再進而計算整理得到一組具有實用性之經驗公式:Sh=αRe^mSc^1/3其中α和m均為有機相體積分率之函數，本研究有機相體積分率的範圍介於10%-40%之間。

關鍵字

質量傳送；二相流；旋轉盤電極

並列摘要

Mass transfer enhancement generated by the presence of unreactive dispersed droplets was investigated on a rotating disk electrode system. Mass transfer rate was determined by limiting current measurements for ferric cyanide ion reduction. The effect of rotating speed, organic volume fraction, and droplet size on the rate of mass transfer has been investigated experimentally. In comparison to mass transfer rate observed with one phase flow system, the higher limiting currents were obtained in the addition of inert droplets of the dispersed phase. A correlation form has been developed for calculation of the limiting current on rotating disk electrode in the dispersed droplets suspensions containing 10%-40% organic volume fraction Sh=αRe^m Se^1/3 where αis 0.908, 1.418, 2.201, 2.505 and m is 0.497, 0.450, 0.403, 0.391, for volume fraction=0.1, 0.2, 0.3, 0.4, respectively. The addition of appreciable volume fractions of dispersed droplets to the one phase solution gives rise to significant improvements in mass transfer rate. The empirically determined criterial equation is of general validity for physically systems, it can develop a basis for designing larger equipment on the basis of this experiments.