Experimental investigation of β-cyclodextrin modified carbon nanotubes nanofluids for solar energy systems: Stability, optical properties and thermal conductivity

Nanofluids have excellent potential for using in the field of heat transfer fluids and particularly for solar energy systems. In this paper, a new and simple chemical synthesis method was conducted to prepare the β-cyclodextrin (β-CD) modified carbon nanotubes (CD-CNTs). The inherent hydrophobic nature of carbon nanotubes was changed and then the homogeneous and highly stable EG-based CD-CNTs nanofluids were fabricated. The results of sedimentation experiment and zeta potential analysis confirmed that the nanofluids exhibited good stability. In addition, the desirable optical properties of CD-CNTs nanofluids were confirmed by transmittance spectra and extinction coefficient. Only 0.01 vol% CD-CNTs nanoparticles could increase the extinction coefficient of pure EG by 4.3 cm−1 approximately. Furthermore, enhancement up to 41.5% in thermal conductivity of nanofluids with volume fractions was found compared to base fluids. And the temperature also put an obvious influence on the thermal conductivity of nanofluids. In summary, the promising features of suitable stability, good optical property and high thermal conductivity ensure the CD-CNTs nanofluids an interesting and advanced HTF in solar energy systems.