Investigation on hybrid nanofluids based on carbon nanotubes filled with metal nanoparticles: Stability, thermal conductivity, and viscosity

Abstract

In recent years, nanofluids as heat transfer fluids have shown huge potential in heat exchange systems. However it is still needed to discover new types of nanofluids with excellent thermal conductivity, dispersion stability and low viscosity to expand its applications. In the present work metal nanoparticles (copper or silver)-filled carbon nanotubes (Cu@CNT, Ag@CNT) have been synthesized by a simple ultrasonic-assisted impregnation combined with chemical reduction. The morphology, phase structure, and degree of crystallization of the prepared nanocomposites have been characterized in detail. Two kinds of nanofluids, including water-based and ethylene glycol-based, have been prepared employing the nanocomposites without adding any surfactant. The dispersion stability, thermal conductivity, and viscosity of the hybrid nanofluids with different mass fraction are studied systematically. The results show that the hybrid nanofluids process good dispersion stability and high thermal conductivity. No obvious delamination can be observed in all nanofluids (0.01–0.05 wt%) after standing for 6 months. The maximum enhancement in thermal conductivity for water-based and ethylene glycol-based Ag@CNT nanofluids with mass fraction of 0.05 wt% reach 52.37% and 40.42% respectively at 65 °C, compared to the base fluid. And the Cu@CNT and Ag@CNT hybrid nanofluids exhibit higher thermal conductivity and lower viscosity than functionalized CNT nanofluids. These results indicate that the metal nanoparticles-filled CNTs composites can be used to improve the thermal conductivity of nanofluids and promote the development of new thermal conductive agents.