Experimental and modeling of CO2 absorption in a bubble column using a water-based nanofluid containing co-doped SiO2 nanoparticles

This study tried to investigate the effect of Co/SiO2 NPs on CO2 absorption in a single raising bubble column (20 °C and 1 atm). Co-doped SiO2 nanoparticles were first synthesized through the chemical vapor deposition (CVD) method, then several nanofluids, including different weight percentages of the synthesized NPs (0.001, 0.01, 0.02, 0.05, and 0.1 wt%) were prepared. Comprehensive experimental studies examined the effect of NPs concentration and nanofluid volume on CO2 absorption rate. The stability of nanofluids, as an affecting factor on nanofluid efficiency, was investigated over 10 days. It was tried to obtain mass transfer parameters, including Sherwood (Sh), and Schmidt (Sc) numbers, incorporating the CO2 diffusivity into the Co/SiO2 nanofluid. Results showed that increasing NPs concentration from 0.001 to 0.02 caused the CO2 absorption rate to reach a maximum point followed by a downward trend. Increasing nanofluid volume was not beneficial for increasing gas absorption, which is attributed to the fact that the predominant mechanism of CO2 absorption was the Brownian motion of NPs. Results confirmed that the prepared nanofluids had acceptable stability over 10 days, and the nanofluid (80 mL), including 0.02 wt% of NPs, had the maximum CO2 absorption, which was 28% more than the base fluid. Findings indicated that the magnitude of the CO2 mass transfer coefficient in the nanofluid was 1.953 * 10− 4 (m.s− 1), which was 1.89 times more than that for the base fluid. Finally, a comprehensive correlation (R2 = 0.99) was introduced to predict the CO2 mass transfer coefficient in the Co/SiO2 nanofluid.