Solidification characteristic enhancement of aqueous nanofluid with different carbon nanotube sizes

Abstract

In this work, the solidification characteristic of aqueous carbon nanotubes (CNTs) nanofluids with various CNTs sizes and concentrations were experimentally investigated. It is indicated addition of surfactant sodium dodecyl benzene sulfonate (SDBS) keeps suspension stability of CNTs nanofluid after solidification-melt cycle, and shows a positive effect during the nucleation region. The results show that subcooling degree and energy storage duration decrease as increasing CNTs concentration from 50 ppm to 2000 ppm. Furthermore, it is found the size of CNTs has a great influence on solidification characteristics. The subcooling degree depression and storage energy acceleration for aqueous nanofluids are more effective as the smaller diameter and longer length of CNTs. A maximum reduction of 47.3% in subcooling degree and 17.8% in charging speed advance were achieved for the CNTs nanofluid with diameter of <8 nm and length of 10–30 um at 500 ppm compared to the deionized water. Moreover, nucleation free energy for five sizes of nanofluids was studied by heterogeneous nucleation in consideration of contact angle and radius of CNTs. The results show the lower nucleation free energy is relevant to the lower subcooling.