An experimental study on β-cyclodextrin modified carbon nanotubes nanofluids for the direct absorption solar collector (DASC): Specific heat capacity and photo-thermal conversion performance

Nanofluids have an advanced application prospect in the community of heat transfer fluids and particularly for the direct absorption solar collector (DASC). But most of body of available researches gave more attention to the thermal conductivity or rheology. We recently reported on the thermal conductivity and optical properties of the beta-cyclodextrin modified carbon nanotubes (CD-CNTs) nanofluids. In this paper, we focused on the specific heat capacity and photo-thermal conversion performance of ethylene glycol-based CD-CNTs nanofluids for DASC system. To this end, a series of CD-CNTs nanofluids with different volume fractions (similar to 0.1 vol%) were prepared. The specific heat capacity decreased with the increase of CD-CNTs loadings and the highest decrement in specific heat capacity was found to be 9.07% for 0.1 vol%. In addition, the temperature had significant effect over specific heat capacity of the studied nanofluids. The volume concentration and irradiation duration time put an effect on the photo-thermal conversion efficiency. In the nanofluid with appropriate concentration, the photo-thermal conversion performance was improved with the extension of light irradiation time, and the possible mechanism of carbon nanotube agglomeration was qualitatively analyzed. In summary, the promising features could ensure the CD-CNTs nanofluids application prospect to be utilized in practical DASC system.