Nanofluid and nanoemulsion absorbents for the enhancement of CO₂ absorption performance

Research on CO₂ capture using nanofluids and nanoemulsions has been actively conducted in recent decades, and numerous studies have achieved improvements in the CO₂ absorption performance of nanofluids and nanoemulsions. In this study, to analyze the enhancement of CO₂ absorption performance achieved by nanofluids and nanoemulsions, experiments are conducted for visualizing the diffusion of CO₂ inside absorbents using the shadowgraph method. The nanofluid absorbents are prepared using SiO₂ solid particles, and the nanoemulsion absorbents are prepared using dodecane as the dispersed phase. The effects of concentration are analyzed through the absorption experiments performed for each concentration. The diffusion coefficient is calculated experimentally and theoretically based on the results of the visualization tests. The absorption of CO₂ begins at the absorbent's upper interface when the CO₂ gas is stationary or moving. The highest absorption is observed at 0.05 vol% of nanoparticles. The absorption performances of the nanofluid and nanoemulsion absorbents are improved by 23.05% and 26.80%, respectively. As CO₂ is absorbed, the absorbent density changes and the Rayleigh convection becomes prominent, resulting in a plume-like flow. The plume formation and growth stages are subdivided into four stages, and both absorbents are compared. The visualization test results indicate that the hydrodynamic effect is a dominant factor in improving nanofluids’ mass transfer and nanoemulsions.