Synergistic approach to colloidal stability and thermophysical optimisation of multi-walled carbon nanotubes, aluminium nitride, and silver-based hybrid nanofluids

Official URL: https://dx.doi.org/10.1016/j.powtec.2025.121348

Efficient thermal management is essential for high-performance applications such as electronics cooling, electric vehicles, and energy systems, where conventional coolants often fail to meet performance demands. This study aims to address the limitations of conventional coolants by formulating and evaluating advanced hybrid and tri-hybrid nanofluids composed of multi-walled carbon nanotubes (MWCNTs), silver (Ag), and aluminium nitride (AlN). A two-step preparation method was employed to formulate various nanofluid formulations and investigate the effects of nanoparticle volumetric ratios and different surfactants, including sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), gum arabic (GA), and sodium dodecyl benzene sulfonate (SDBS) on colloidal stability, heat transfer characteristics, and cost-effectiveness. Nanofluid formulations were prepared using volumetric ratios of 80:20, 60:40, 40:60, and 20:80 for hybrid combinations, and 20/20/60, 20/40/40, and 20/60/20 for tri-hybrid mixtures, and analysed over a temperature range of 20 to 45 °C. Experimental results revealed that SDBS consistently outperformed the others, by maintaining a stable suspension and thus preserving the enhanced thermal properties over extended periods. Among all tested nanofluids, MWCNTs exhibited the highest thermal conductivity enhancement of 8.57 %. The tri-hybrid formulation with a 20/60/20 MWCNTs/Ag/AlN ratio achieved a comparable enhancement of 8.14 %, demonstrating that optimised combinations of nanoparticles can simultaneously deliver high thermal performance, good stability, and reasonable cost-efficiency. However, this tri-hybrid formulation also showed the highest viscosity increase noted to be 5.55 %, compared to a 4.43 % increase for simple Ag nanofluids. Additionally, the highest density increase was 0.25 % for Ag, while the highest among hybrid combinations was 0.22 % for the 80/20 Ag/AlN mixture. Finally, among tri-hybrid formulations, the 20/60/20 ratio showed the highest increase of 0.19 %, whereas the 20/40/40 ratio exhibited a more moderate increase. Cost analysis indicated that the tri-hybrid nanofluid with a 20/40/40 ratio is the most cost-effective option when cost considerations are as important as thermal performance. However, for applications where maximising thermal performance is crucial, the tri-hybrid with a 20/60/20 ratio is the preferred choice. This work contributes new insights into the development of multifunctional nanofluids and presents comprehensive investigations into MWCNTs, Ag, and AlN-based tri-hybrid formulations.