Physiochemical studies of functionalized MWCNT/transformer oil nanofluid utilized in a double pipe heat exchanger

Abstract

The transformer-oil based nanofluid suspensions were prepared by adding 0.05 to 0.80 wt% multi-wall carbon nanotubes (MWCNTs) functionalized with a –COOH group. Sodium dodecyl sulfate (SDS) was used to stabilize the suspensions. The resulting material was used as a coolant in a double pipe heat exchanger operated under co- and counter-current flow conditions. The nanofluid thermo–physical features such as the thermal conductivity, viscosity, and density were determined at various temperatures and mass fractions. Then, pertinent semi-empirical relations were developed. To verify any MWCNT and SDS interactions with the material, the Fourier-transform infrared analysis was performed. Moreover, the stability of the nanofluid suspension was understudied through the UV–vis and thermogravimetric analysis techniques. In addition, the maximum heat transfer coefficient improvement was determined to be 86.7% at a MWCNT mass fraction of 0.8 wt%. Meanwhile, average increments of the overall heat transfer coefficient and thermal conductivity of the prepared nanofluid were revealed about 37.2% and 138%, respectively in comparison with that of the base fluid. Furthermore, the optimum thermal conductivity of 0.388 W/m.K was obtained at 45 °C and 0.8 wt% of the MWCNT. Ultimately, a sensitivity analysis emphasized that, the understudied system’s behaviors were within an accuracy limit of ± 97%.