Experimental investigation of indirect heat transfer through a novel designed lab-scale setup using functionalized MWCNTs nanofluids (MWCNTs-COOH/water and MWCNTs- OH/water)

This study aims to investigate the influence of functionalized multi-walled carbon nanotubes (MWCNTs-COOH and MWCNTs-OH) on the performance of a novel indirect laboratory heater redesigned with a helical tube. Experiments were performed using a bath of water and the two nanofluids mentioned above. The nanofluids were prepared at concentrations of (0.025, 0.05, 0.075, and 0.1) wt%. To ensure the stability of the utilized nanofluids and the structure of the nanoparticles, characterization studies such as dynamic light scattering (DLS), FT-IR, and XRD were carried out. The results indicated that when concentration levels rose, the system's performance rose as well. For instance, the MWCNTs-COOH nanofluid bath had a maximum heat transfer rate of 1709 W, which was 19.04% better than pure water, and a maximum Nusselt number of 15.61, which was an increase of 36.33% over pure water. In summary, heat loss increased with an increment in flow rate, and by increasing the concentration of nanofluids, the lowest heat loss, the highest heat transfer rate, and the best efficiency of the system were ach-ieved. This study can establish the foundation for redesigning indirect heaters to reduce thermal energy consumption and for further research on the use of nanofluids in indirect bath heating.