Mass transfer performance enhancement by nanoabsorbents during CO₂ absorption process

A fluid in which nano-sized particles are dispersed is called nanofluids. It has been actively studied in the field of heat and mass transfer because of its attractive thermophysical properties. Since methanol is mainly used as a physical CO₂ absorbent, methanol-based nanofluids (nanoabsorbents) are tested for mass transfer performance enhancement. Al₂O₃ and SiO₂ nanopowders are used, and the nanoabsorbents are manufactured by the ultrasonication method. Thermal conductivity (0.005–1.0 vol%, 24–40 °C), viscosity (0.005–1.0 vol%, 20 °C), surface tension (0.005–0.1 vol%, 20 °C) and average cluster size (0.005–1.0 vol%, 20 °C) are measured to analyze the combined heat and mass transfer and the dispersion characteristics of the nanofluids. Also, the mass transfer characteristics between CO₂ and nanoabsorbents is evaluated using the Schlieren visualization experiment. It is found that the thermal conductivity and viscosity of the nanoabsorbents increase with increasing the volume concentration of nanoparticles. At 1.0 vol%, the thermal conductivities of Al₂O₃/methanol and SiO₂/methanol nanoabsorbents are 4.6% and 5.5% higher than that of pure methanol, respectively, while the viscosities are also increased by 21% and 11%, respectively. The average cluster sizes of Al₂O₃ and SiO₂ nanoabsorbents are not vary depending on the volume concentration, and they range 267–288 nm and 496–507 nm, respectively. It is concluded that the mass diffusivities of nanoabsorbents are significantly higher than that of pure methanol, and the enhancement mechanism of mass transfer is newly proposed.