Thermal properties measurement and performance evaluation of water/ZnO nanofluid in a mini channel with offset fins

Abstract

The present study experimentally and numerically investigated the heat transfer and flow behavior of ZnO/water nanofluid in a mini channel with offset fins with a 1.59mm hydraulic diameter. The thermal properties including density, viscosity and thermal conductivity with 0.75% and 1.5% volume concentration were measured and compared with correlations firstly. Then, the thermal and flow characteristics under different operational conditions were evaluated. Results indicate that the existing correlations can desirably predict the density and thermal conductivity but heavily underestimate the viscosity. The existence of offset fins eliminates the obvious transition zone from laminar flow to turbulent flow. Even though the Nusselt number of nanofluid can be improved by 7.9% and 10.5% averagely for concentrations of 0.75% and 1.5%, the friction factor is also significantly enlarged. The heat load shows negligible impact on the flow and heat transfer performance. For the thermal performance factor, its value is around 1 under different concentration and Reynolds number, which means that no benefit will be brought about by nanofluid considering both thermal and hydrodynamic performance. As the existing correlation fails to accurately predict the Nusselt number, a new correlation is put forward with a MARD of 1.7% for ZnO nanofluid flow in mini channel with offset fins. Numerically, the simulation results of single-phase, mixture and Eulerian model were compared with experimental ones. It is found that the single-phase model gives the best prediction of Nusselt number with a MARD of 8.64%. In addition, the mixture model has the smallest prediction derivation of friction factor with a MARD of 18.8%.