Solid‐Volume‐Fraction Retained Tailoring of Thermal Diffusivity of Multiwalled Carbon Nanotube Nanofluid: A Photothermal Investigation.

The diversified forms of heat engines necessitate developing energy‐efficient engine oils and coolants. The article proposes a method of thermal diffusivity tuning of the base fluid (ethylene glycol) using multiwalled carbon nanotubes (MWCNTs), annealed at different temperatures, without altering the solid volume fraction. Having studied the annealing‐induced structure modifications of MWCNTs through thermogravimetric and spectroscopic studies, the thermal diffusivity variations are investigated through the sensitive photothermal mode‐mismatched dual‐beam thermal lens technique. The study reveals that the annealing‐induced structure modifications lower the nanofluid's thermal diffusivity and unveils the existence of transition annealing temperature of MWCNTs above which the nanoparticles can make the nanofluid a heat trapper. The study also proposes the importance of making more energy‐efficient engine oils by keeping the temperature of the engine oil below the transition temperature. [ABSTRACT FROM AUTHOR]