WHICH PARAMETER SHOULD BE USED IN EVALUATING NANOFLUID FLOWS: REYNOLDS NUMBER, VELOCITY, MASS FLOW RATE OR PUMPING POWER?

The heat transfer, fluid flow, and entropy generation characteristics of a diamond-Fe3O4/water hybrid nanofluid are investigated numerically for different nanoparticle volume fractions under laminar flow conditions. In addition, diamond/water and Fe3O4/water nanofluids are investigated to compare with their hybrid form. The results are presented at the given Reynolds number, velocity, mass flow rate, and pumping power. As a result, overabundant enhancements are observed in thermal performances of nanofluids when evaluation is realized for the same Reynolds number. At Re = 2000, a diamond-Fe3O4/water hybrid nanofluid (phi = 0.2%) provides a convective heat transfer enhancement of 30.31%. However, at V = 1.3 m/s, the convective heat transfer coefficient obtained for a diamond-Fe3O4/water hybrid nanofluid (phi = 0.2%) is 2.17% higher than that of pure water. It is also observed that pure water has a better convective heat transfer rate compared to a diamond-Fe3O4/water hybrid nanofluid when the evaluation is performed at the same pumping power. Among all evaluation parameters, it is found that there is a minimum entropy generation point. Although it is difficult to decide, but the results obtained with evaluation performed at the same velocity or the same pumping power can be more realistic and reasonable.