Comparison of single-phase Newtonian and non-Newtonian nanofluid and two-phase models for convective heat transfer of nanofluid flow in backward-facing step

The aim is to investigate the application of nanofluids for improving the heat transfer in a backward-facing step channel. Numerical simulations are performed using single-phase models for both Newtonian and non-Newtonian fluids in the Reynolds number range 280–470. Constant and temperature-dependent thermo-physical properties of different volume fractions (0–4%) of nanoparticles are considered. The thermal enhancement of the nanofluids within the channel is analyzed and compared with the experimental data. A detailed comparison of different CFD models is established. Numerical results are obtained with two types of single-phase models (Newtonian and non-Newtonian) and three types of two-phase models (mixture, volume of fluid (VOF), Eulerian) and compared with experimental results obtained for the Nusselt number . The finite volume method is used to solve the system of governing partial differential equations describing the steady-state, two-dimensional, laminar, mixed convective flow in a micro backward facing step channel with uniform heat flux. The single-phase and two-phase models predict practically equivalent hydrodynamic fields, but significantly different thermal fields are observed in our results. The performance efficiency coefficient (PEC) is determined using single-phase and two-phase methods for Al 2 O 3 -water nanofluids at different Reynolds numbers to investigate their thermal performance.