Gas Absorption from a Row of CO₂ Bubbles in Tap Water under Controlled Bubble Generation

Abstract

The correlation between liquid-phase mass transfer coefficient (k_L) and gas–liquid interfacial area (A) was measured within a CO₂–tap water system. An audio speaker was used to control both the bubble generation frequency (f) and bubble diameter. The bubble diameter was varied between 0.4 mm and 9.8 mm, and f was set to 10, 30, or 60 Hz. The maximum standard deviation of the volume equivalent diameter of bubbles just after generation from the nozzle was approximately ≤1/10 of the average diameter. Depending on the bubble diameter, one of two different methods was used to measure the effect of bubble diameter on k_L. The results indicate that for bubbles with a diameter greater than 5 mm, k_L depends on f. For f=10 Hz, the relationship between k_L and the bubble diameter was similar to that of an empirical correlation of a pure system described in the literature (Clift et al., 1965). For bubbles with a diameter 0.58 mm or less, k_L decreased with decreasing bubble diameter. The mass transfer of CO₂ bubbles in this release method correlated with the conventional dimensionless equation based on the relationship between the Sherwood (Sh) and Reynolds (Re) numbers. Sh was proportional to Re^1/2 for 5<Re<60, and Sh was proportional to Re^3/4 for 300<Re<3300. The dependence of Re on Sh for a row of bubbles was revealed to be similar to that for single bubbles.