Photo-thermal conversion properties of hybrid CuO-MWCNT/H2O nanofluids for direct solar thermal energy harvest

Abstract

Water-based hybrid nanofluids with CuO and multi-walled carbon nanotube (MWCNT) were prepared and well dispersed. The optical absorption properties and photo-thermal conversion performance of hybrid CuO-MWCNT/H2O nanofluids at different concentration mixing ratios (CMRs) were experimentally tested and compared to evaluate the solar thermal energy harvest capability. The mixture of CuO-MWCNT nanofluids significantly enhanced solar energy spectral absorption as compared with individual CuO or MWCNT nanofluids, and the extinction coefficients of hybrid nanofluids were mostly equal to the sum of individual components. At appropriate CuO/MWCNT CMRs, the solar weighted absorption fractions of hybrid nanofluids are almost 100% at an optical penetration distance of 1 cm. Besides, the photo-thermal conversion performance of hybrid nanofluids was largely superior to individual nanofluids but highly dependent on the CMR, and an excessive addition of individual component could lower the performance. At a CuO/MWCNT CMR of 0.15 wt%/0.005 wt%, a maximum terminal temperature rise of 14.1 °C was achieved with respect to DI water after a light irradiation time duration of 45 min. The coexistence and interaction of CuO nanoparticles and MWCNT fibers in the aqueous suspension at evaluated temperatures were took into account to explain the optical absorption behavior and then the photo-thermal conversion properties. This study suggests that hybrid CuO-MWCNT/H2O nanofluids at appropriate CMRs provide a potential alternative in direct solar thermal energy harvest.