Dispersion regimes in alumina/water-based nanofluids: Simultaneous measurements of thermal conductivity and dynamic viscosity

The present work proposes a detailed experimental analysis of the dispersion regimes within nanofluids. For this purpose, simultaneous measurements of thermal conductivity and dynamic viscosity are performed for alumina/water-based nanofluids at volumetric concentrations phi ranging from 0.2 to 2%. Depending on the pH values, five dispersion regimes have been identified for intermediate values of phi. The well-dispersed regime characterized by a local maximum of the thermal conductivity and an absolute minimum of the dynamic viscosity is not recovered for phi = 2%, while the chain-like agglomeration regime is not observed for phi = 0.2%. The results are corroborated by the distribution of the Mouromtseff number, which appears as a reliable parameter to identify the most efficient nanofluids. For an optimized nanofluid, comparable efficiency may be achieved even at low concentration phi = 0.2%.