Effects of Bubble Interactions on Liquid Phase Mass Transfer Coefficients in Three Types of Bubble Columns

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This work investigates a mechanism and degree for bubble interactions such as bubble clustering, coalescence and breakup to affect the liquid phase mass transfer coefficient kL. Our previous kL data for a normal bubble column (NBC), internal loop airlift (ILBC) and external loop airlift (ELBC) are compared with kLS for single bubbles and kL,BF in the bubble flow (BF) at a fixed mean bubble diameter dB. Our correlations of kL∝εG0.1 (NBC and ILBC) and kL∝εG0.2 (ELBC) have been found to arise from the relationship for gas holdup εG=0.5(dB/l)3, where l is the mean distance between the adjacent bubbles. The reported kL,BF values were reproduced by the Higbie model with the average bubble slip velocity of (gdB/2)0.5. A factor F=kL,CTF/kL,BF is defined to quantify an effect of the bubble interactions on kL,CTF in the churn-turbulent flow (CTF). The reported correlation gives F=0.5Eo3/8, where Eo=gdB2ρL/σ. Eo<6.4 and Eo>6.4 have been found to give the clustering regime and the coalescence and breakup regime, respectively. Our kL,CTF data (NBC and ILBC) satisfied F=0.5Eo3/8. F=kL,ELBC/kL,BF for the ELBC roughly correlates as F=1.3.