Enhancement mechanisms of mass transfer performance by nanoabsorbents during CO₂ absorption process

In this study, the hydrodynamic characteristics and enhanced mass transfer performance of CO₂ absorption in the presence of Al₂O₃ nanoparticles are studied. A combined VOF-DPM model that can predict the characteristics of nanoparticles in gas–liquid system is developed. The gas bubble and liquid are modeled as the Eulerian phases by the volume-of-fluid (VOF) method, while the nanoparticles are tracked as the Lagrangian phase by the discrete particle model (DPM). The coupling interaction between phases was considered by adding the interchange terms to the momentum equation. Then a systematization of phenomena on both liquid and gas field that related to the motion of nanoparticles was presented, involving the turbulence in local liquid, dynamical deformation of gas bubble, and the distribution of gas velocity. Accordingly, the enhanced interfacial mass transfer was predicted and verified by experimental results. It was found that the interfacial flow, that is, the local turbulent motion of liquid, makes it possible for the nanoparticles to penetrate into the bubble surface. The penetrating particles, on one hand, disturb the velocity distribution inside the bubble, improving the fluid renewal at the gas–liquid interface. On the other hand, they play a shuttle role to carry CO₂ gas between the gas phase and the interface. Finally, it is concluded that the nanoparticle-induced hydrodynamic effect dominates the CO₂ absorption by improving the interfacial mass transfer.