(5) The gas holdups in air–water bubble columns with various initial liquid heights are well correlated in terms of the Froude number defined by using the superficial gas velocity and the initial liquid height.
(6) The empirical correlation of aG is applicable not only to the present rectangular and cylindrical columns but also to the cylindrical bubble column with different diffuser configura- tions by tuning the model coefficients.
Acknowledgements
The authors would like to express their thanks to Mr. Kengo Uchida for his assistance. This work has been supported by the Japan Society for the Promotion of Science (JSPS) (Grants-in-Aid for Scientific Research (B), No. 15H03920).
Appendix A
All the data of gas holdups in the rectangular and cylindrical columns are summarized in Tables A1 and A2, respectively.