Bubble behaviors and CO₂ absorption characteristics in nanoabsorbents

The objectives of this study are to present a comprehensive analysis of the CO₂ bubble population dynamics and to investigate their effects on the CO₂ absorption characteristics in nanoabsorbents (methanol with various concentrations of Al₂O₃ nanoparticles) with a rectangular bubble column. The population balance model (PBM) as a well-established method based on the Euler-Euler model is employed to compute the size distribution of bubbles and to account for the bubbles coalescence and breakage in multiphase flow. The coupled volume-of-fluid (VOF) method is selected to clearly capture the coalescence and breakup processes of successively rising bubbles. The results show that there is a significant influence of the leading bubble on the following one, including the increment of the velocity, the deformation of the bubble shape and the flow instability. It is also found that the critical distance at which the influences can be exerted is related to the bubble wake trailed by the leading bubble. Accordingly, five types of bubble wakes and their effects on the bubble behaviors such as the coalescence and breakup are categorized. Finally, by further analyzing the bubble behaviors in methanol with different volume fraction of Al₂O₃, it is found that the coalescence and breakup of bubbles are dominated by the bubble wake and enhanced by the eddy in local liquid. It is concluded that the higher concentration of nanoparticles is favorable to the bubble coalescence and breakup, which enhance the mass transfer performance by increasing the interfacial area.