Enhanced solar thermal conversion and thermal conduction of MWCNT-SiO₂/Ag binary nanofluids

The features of working fluids which enable synchronously high solar thermal conversion within broadband wavelength ranges and high heat transport are extremely vital for direct volumetric solar receivers. By making use of unique different spectral absorption behaviors of unitary nanofluids, in this paper, we study feasibility of binary nanofluids with enhanced solar thermal conversion and thermal conduction. The binary nanofluid contains multi-wall carbon nanotubes (MWCNTs) and silica/silver (SiO₂/Ag) plamonic nanoparticles. Instead of the limited absorption property of unitary nanofluids, by mixing different types of nanofluids with different spectrally absorptive features in proper manners, the spectral absorptance of binary nanofluids can be adjusted by controlling the ratio of two components. Since MWCNTs have high absorption in infrared spectra while SiO₂/Ag nanoparticles have strong absorption peaks within visible spectra, the mixed nanofluid get higher absorption within wider solar spectra. Meanwhile, the existence of MWCNTs in the working fluid remarkably improves energy transport of the binary nanofluid. Specifically, MWCNT with the volume fraction of 0.1% can enhance the thermal conductivity of about 7%. The favorable light absorption and heat transfer performance can lead to the higher light absorption efficiency. This work provides a new strategy to improve the solar energy harvesting efficiency of nanofluids being used for volumetric solar collectors.