Mass transfer performance enhancement by nanoabsorbents during CO2 absorption process

Abstract

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.