Thermal performance investigation of Therminol55/MWCNT+CuO nanofluid flow in a heat exchanger from an exergy and entropy approach

Nanofluids have been extensively studied in recent decades and have been regarded as "next-generation heat transfer fluids" due to their superior properties. However, dispersion stability and application at higher temperatures are among the challenges that must be overcome. In this work, a new class of stable hybrid nanofluid based on multi-walled carbon nanotube (MWCNT) + cupric oxide (CuO) nanocomposite is produced with Therminol55 (TH55) as the base fluid. Nanofluids' thermophysical characteristics are investigated at varying concentrations (0.005-0.08 wt%), and they are subsequently employed as the heat transfer medium in a tube heat exchanger (HEX) for the turbulent flow regime. Thermal conductivity was significantly increased by 128.4% at the maximum nanocomposite concentration of 0.08 wt%. Despite this, nanocomposites enhanced the nanofluids' viscosity, which climbed gradually with concentration to a maximum enhancement of around 25% at 0.08 wt%. The heat transfer performance of the formulated nanofluids was numerically assessed and found to be good; for example, when compared to pure TH55, the heat transfer coefficient improved by up to 128%. The highest increase in Nu was 38.4%, while the maximum increase in pumping power was determined to be 103.88%. Furthermore, the maximum exergy efficiency was 47.84% at a 0.08 wt% concentration and a Reynolds number (Re) of 12500, which is somewhat higher than the 40.96% attained with pure TH55. The highest thermal performance factor was 1.31 for 0.08 wt %, exceeding the maximum thermal performance factors of 1.17, 1.11, 1.08, and 1.03 for 0.04, 0.02, 0.01, and 0.005 wt %, respectively. Consequently, a nanofluid made of MWCNT + CuO/TH55 might be a promising candidate for usage as a heat transfer fluid.