Gas–liquid mass transfer enhancement in the presence of nanoparticles under slug flow in microreactors

Nanofluids containing nanoparticles represent a promising solvent or reaction system for gas–liquid operations. Herein, the effect of nanoparticle (Al 2 O 3 and SiO 2 ) addition on gas–liquid slug flow pattern and mass transfer enhancement was investigated during CO 2 absorption into water in microreactors. Nanoparticle addition reduced bubble length, especially at higher concentrations possibly due to increased shear stress role in bubble breakup. Increasing the gas–nanofluid flow ratio, nanofluid flow rate and concentration, or decreasing its size enhanced the overall liquid‐side volumetric mass transfer coefficient ( k L a ). Besides, dispersing Al 2 O 3 nanoparticles improved k L a more remarkably than SiO 2 . Existing theoretical or empirical correlations for gas–liquid systems in microreactors are inadequate to predict the measured k L a when considering nanofluids just as pseudo‐homogeneous fluids with proper physical properties. This inadequacy, as well as the superior k L a in CO 2 ‐nanofluid system compared with CO 2 ‐water system, suggests additional mass transfer enhancement by the shuttle effect and adsorptive capacity of nanoparticles.