Study on the heat transfer characteristics of MWCNTs and Ni-MWCNTs nanofluids based on the 3<i>ω</i> method

Abstract

Compared to pure multi-walled carbon nanotube (MWCNT) nanoparticles, metal-modified MWCNT nanoparticles might have better thermal conductivity. We prepared 10# transformer oil (TO)/MWCNT, ethylene glycol(EG)/MWCNT, and EG/Ni-MWCNT nanofluids with different concentrations and characterized their thermophysical parameters by the 3ω method. The results demonstrate that the MWCNT nanoparticles significantly enhance the thermal conductivity of the base fluid, with Ni-MWCNTs exhibiting even greater improvement. The increase in nanoparticle concentration and particle size is conducive to heat transfer. At different temperatures, the thermal conductivity of the MWCNTs in TO and EG base fluids exhibited distinct trends, driven by the predominant influence of the base fluids. The calculated heat capacity exhibits a decreasing trend with rising temperature, originating from the synergistic effects of thermal resistance and interfacial thermal resistance between the base fluid and nanoparticles. Furthermore, pH experiments on the nanofluids revealed that both MWCNT and Ni-MWCNT nanofluids indicate parabolic variations in thermal conductivity over the pH range of 2–14. These findings were synergistically corroborated by concurrent sedimentation analysis and light transmittance measurements, demonstrating that pH-induced alterations in nanofluids stability govern the thermal conductivity changes. The TO base fluid demonstrates superior dispersion stability under alkaline conditions, primarily attributed to the unique hydrophobic nature of the oleophilic matrix. The steric hindrance effect formed between nanoparticles effectively suppresses their agglomeration.