Numerical Estimation of Local Gas Holdup in Gas-liquid Contactors

氣液反應器中局部氣含量之數值模擬

巫鴻章(Hong-Zhang Wu) ； 呂維明(Wei-Ming Lu)

《Journal of the Chinese Institute of Chemical Engineers》 33卷5期 (2002/09) Pp. 429-437

https://doi.org/10.6967/JCICE.200209.0429

摘要

利用CFX4.1計算多相流的功能結合氣泡結合與撕裂的模式，本研究提出可估算氣泡塔與通氣攪伴槽中局部氣含量分佈的數值模擬方法。將所計算出來的局部氣含量值積分累加，得到系統之整體氣含量值，將其與實驗觀察通氣前後系統液面的上升高度相比較，發現兩者的結果極為接近，顯示此模擬方法具有高度準確性。欲更進一步確認此方法的可信度，本人另以此法計算氣泡塔中的氣相與液相的流態，並將結果與文獻中Delnoij et al. (1997) 所拍攝的影像相比較，結果發現當攪拌槽中的通氣數小於0.03，抑或氣泡塔在homogeneous regime下操作時，計算所得之氣液相流態與局部氣含量值均與實驗方法所得者極為接近，顯示本研究所提出之模擬方法可適用於計算通氣攪拌槽與氣泡塔中多相流流態與相關性質之計算。

並列摘要

Using the multi-phase flow simulation facility described in the software CFX 4.1 and by incorporating bubble breakup and bubble coalescence models, a numerical method was developed and applied to estimate the local gas holdup distribution within bubble columns and aerated stirred vessels under various operating conditions. The calculated local gas holdup values were integrated into the overall gas holdup of the system. The accuracy of the overall as holdup value under a certain condition was verified by comparing it with an experimental value, which was the liquid height difference before and after aeration obtained by means of visual observation. To assure the applicability of this numerical approach to the gas-liquid flow system, transient gas-liquid f1ow patterns in bubble columns were also calculated and compared with the snapshots of Delnoij et al. (1997). It is found that both the local and overall gas holdup values show fairly good agreement with the experimental ones if the gas within the aerated stirred vessel is dispersed effectively (NA＜0.03) and the bubble column is operated in the homogeneous regime. The results obtained in this study indicate that the proposed numerical approach can be used to reliably predict gas and liquid flows in stirred vessels and bubble columns.

並列關鍵字

Stirred vessel ； Gas recirculation rate ； Numerical method ； Gas holdup ； Bubble column