High temperature and long-term stability of carbon nanotube nanofluids for direct absorption solar thermal collectors

Abstract

Stable dispersions (nanofluids) are produced using plasma functionalized multi-walled carbon nanotubes (MWCNTs). To our knowledge, this study presents a first quantitative demonstration of nanofluid stability over extended periods of time (currently tested up to 8months) and after intense heating. No agglomeration is found to occur in the water and glycol-based nanofluids after heating at 85 and 170°C, respectively. Significant agglomeration does occur for suspensions produced using the non-polar Therminol® VP-1 heat transfer fluid. Optical characterization of the nanofluids demonstrates that the MWCNTs are highly absorbing over the majority of the solar spectrum, allowing for close to 100% solar energy absorption, even at low concentrations and small collection volumes. These absorption properties coupled with the stability of the nanofluids make them ideal candidates as direct solar thermal collectors.