An experimental study of the influence of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT nanoparticles on the thermophysical characteristics and laminar convective heat transfer of nanofluids: A comparative study

Abstract

In this study, the main objective is to investigate the impact of single, hybrid, and doped magnetic nanoparticles (NPs) on the convective heat transfer capabilities of a water/ethylene glycol (EG)-based nanofluid (NF) under the influence of a magnetic field (MF). The NFs were prepared by incorporating Fe3O4, Fe3O4-multi-walled carbon nanotubes (Fe3O4-MWCNT), and Fe3O4@MWCNT in concentrations of 0.05, 0.1, and 0.2 wt.%. The NPs were characterized using various techniques such as XRD, SEM, VSM, Raman spectroscopy, and FTIR to confirm their properties. The stability of the NFs was assessed through dynamic DLS and zeta potential measurements. The study then focused on evaluating the effects of these nano-additives on thermal conductivity (TC), viscosity at 25 °C, convective heat transfer coefficient (CHTC), and friction factor in a circular tube under laminar flow regime with a constant wall flux, both with and without the application of a MF. The results of present preliminary study with limited samples revealed that the CHTC of NFs containing Fe3O4 and Fe3O4@MWCNT NPs increased with NP concentration and application of a MF, with maximum increases of approximately 19.01 % and 32.84 %, respectively. However, in the case of NFs containing MWCNT-Fe3O4 NPs, the CHTC decreased when the MF was applied at concentrations higher than 0.1 wt.%. Furthermore, the NFs containing 0.2 wt.% of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT NPs exhibited the highest friction when subjected to a 400 G MF, resulting in increases of 5.2 %, 9.2 %, and 5.9 %, respectively, compared to the base fluid. The performance index, which assesses the effectiveness of using NFs instead of the base fluid, indicated that all samples had a performance index greater than one, indicating their efficacy. The maximum performance index achieved was 1.343, corresponding to the NF containing 0.2 wt.% of Fe3O4@MWCNT NPs at a Reynolds number (Re) of 2200 and a MF strength of 400 G.