Thermodynamic performance of Al2O3-Cu-CuO/water (W) ternary nanofluids in the full-flow regime of convective heat transfer

To explore the convection mechanisms of ternary nanofluids in the full-flow regime (laminar-transition-turbulent regime), the thermodynamic performance of Al2O3-Cu-CuO/W ternary nanofluids (with a volume fraction of 0.02 vol%) and their corresponding mono nanofluids was investigated in Reynolds number (Re) range of 800-8000 in a cylindrical tube. The results showed that the presence of suspended particles in the Al2O3-Cu-CuO/W nanofluids caused the transition regime to shift to a lower Re value of similar to 1900. As Re was increased, the heat transfer performance exhibited a fluctuating upward trend, with a maximum at Re = 5250. Further, the ternary nanofluid with a mixing ratio of 30:30:40 showed a Nu 1.73 times that of the base fluid, with the corresponding values for the CuO/W and Al2O3/W nanofluids being only 1.36 and 1.39 times, respectively. Moreover, the thermal conductivity of the ternary nanofluids had a substantial impact on heat transfer performance in the laminar regime, with a correlation coefficient, r, of 0.6429, but less of an influence in the turbulent regime, with an r value of only 0.5. Finally, the optimum mixing ratio for the convective heat transfer process was determined to be 30:50:20 based on the values of Nusselt number enhancement rate and enhanced heat transfer factor, as well as on thermodynamic analysis of the system entropy generation and exergy.