Extinction coefficient measurement of supercritical water-based multi-walled carbon nanotube nanofluids

This study measured the extinction coefficients of supercritical water (SCW)-based multi-walled carbon nanotube (MWCNT) nanofluids by using an in-house developed chamber. A He–Ne laser with a wavelength of 632.8 nm was employed as the light source. Rod-shaped quartz with a diameter of 3 mm and a length of 305 mm was installed at the top and bottom of the chamber so that the laser could pass through the chamber. To maintain the SCW-based MWCNT nanofluids in the chamber, the chamber was designed to reach up to 400 °C and 30 MPa. Based on the experimental data, it is shown that the extinction coefficient of the SCW-based MWCNT nanofluids linearly increases within the range of the volume fraction from 0 to 0.02 vol. % and belongs to the independent scattering regime. Moreover, the enhancement of the extinction coefficient of the SCW-based MWCNT nanofluids shows promise as a working fluid for ultra-high temperature solar thermal systems, such as concentrated solar power plants.