Nathan Hordy

Thermal stability of carbon nanotube-based nanofluids for solar thermal collectors

Abstract Carbon nanotube dispersions are promising candidates for use as working fluids in high-performance solar collectors. However, one major stumbling block in the way of their widespread application is the difficulty in achieving stable nanofluid suspensions at elevated temperatures. In this study, the stability of plasma- and acid-functionalised multi-walled carbon nanotube dispersions at temperatures up to 150°C was investigated. Therminol 55 and propylene glycol were used as the main solvents, while water was used as a reference solvent. The results of UV-VIS-NIR absorption spectroscopy showed that no agglomeration occurred in the plasma-functionalised multi-walled carbon nanotube nanofluids heated to 150°C. However, minor variations were observed in the absorbance of acid-functionalised multi-walled carbon nanotubes in propylene glycol and therminol 55 base fluids at high temperatures.

A stable carbon nanotube nanofluid for latent heat-driven volumetric absorption solar heating applications

Recently, direct solar collection through the use of broadly absorbing nanoparticle suspensions (known as nanofluids) has been shown as a promising method to improve efficiencies in solar thermal devices. By utilizing a volatile base fluid, this concept could also be applied to the development of a direct absorption heat pipe for an evacuated tube solar collector. However, for this to happen or for any other light-induced vapor production applications, the nanofluid must remain stable over extended periods of time at high temperatures and throughout repetitive evaporation/condensation cycles. In this work, we report for the first time a nanofluid consisting of plasma-functionalized multiwalled carbon nanotubes (MWCNTs) suspended in denatured alcohol, which achieves this required stability. In addition, optical characterization of the nanofluid demonstrates that close to 100% of solar irradiation can be absorbed over a relatively small nanofluid thickness.