Comparison of stability and thermophysical properties of CNT-GNP hybrid nanofluids using different surface modification techniques

This study examines how non-covalent and covalent surface modification methods affect the stability and thermo-physical characteristics of carbon nanotubes (CNTs) and graphene platelets (GNP) when distributed in solar thermal fluids. Surfactants are employed for examining non-covalent surface modification, while acid treatment is utilized for investigating covalent modification. Nanofluid samples are created with concentrations of 0.0625%, 0.125%, 0.25%, and 0.5% by weight in pure ethylene glycol (EG) and EG-water (80:20). Zeta potential analysis was utilized to study the stability of the nanofluids. The oxidized CNT-GNP nanofluids showed outstanding stability, with zeta potential values remaining almost constant for 60 d. Experiments were conducted on pure, surfactant-dispersed, and oxidized CNT-GNP nanofluids. The thermal conductivity of oxidized CNT-GNP nanofluids increased by 16% when 0.5 wt% was dispersed in the EG-water (80:20) sample. Nanofluids with CTAB and SDS showed a 14% and 13% enhancement in thermal conductivity, respectively. Formulas were created to forecast thermal conductivity and dynamic viscosity values.