Two-bubble class model

A Two-Bubble Class Model for Churn Turbulent Bubble Column Slurry Reactor... 

The application of the two bubble class model is important for reactions which are mass transfer controlled. The scale-up of a mass transfer controlled operation based on a fixed gas phase residence time assumes incorrect and higher actual gas velocities. Thus, when the flow regime changes from... 

The two bubble class model is applied here to the absorption of CO2 in NaOH, which conforms to a fast pseudo-first order reaction under certain operating conditions (15). In the data reported by Schumpe et al. ( 7 ), COo was absorbed during cocurrent flow in NaOH solution in a 0.102 m diameter bubble column. The gas phase consisted of approximately 10 vol % of CO2 in N2. The gas velocities ranged from 0.025 to 0.15 m/s. Since the churn turbulent regime prevailed for gas velocities greater than approximately 0.07 m/s, only the data in the range 0.07 m/s to 0.15 m/s were considered. 

Figure 3 shows a comparison between the conversions predicted by the two bubble class model and the experimentally measured values of Schumpe et al. ( 7). In the theoretical calculations, the small bubble diameter was chosen to be 1 mm based on physical observations made by several investigators. As shown in Table III, the predicted conversions were, however, found to be relatively insensitive to the small bubble diameter. In these calculations, the small bubble diameter was varied from 1 mm to 3 mm and little effect on the conversions was observed. 

Figure 3. Comparison between conversions predicted by Two-Bubble-Class model and experimental values of Schumpe et al. (7).

From the results described above, it is seen that the two bubble class model predicts conversions that fit the experimental data. The predicted conversions were obtained with the assumption that the large bubble size varies somewhat with the gas velocity. Thus it is required to have a knowledge of the large bubble diameter (as a function of gas velocity) to properly evaluate the validity of this model. 

Figure 5. Comparison between Plug Flow model and Two-Bubble-Class model outside range of experimental velocities. ( - Plug Flow model, A - Two-Bubble-Class model, varying d , H— Two-Bubble-Class model, d = 10 mm).

Joseph, S. and Y.T. Shah. A Two-Bubble Class Model for Churn Turbulent Bubble Column Slurry Reactors. ACS Symp. Series 27 (1984) 149-167. 

Jiang X, Yang N, Zhu J, et al On the single and two-bubble class models for bubble column reactors, Chem Eng Sci 123 514-526, 2015. 

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