Turbulent forced convection flow of water-based nanofluids with temperature-dependent properties over backward-facing step channel with upwardly deflected downstream wall

Abstract

The heat transfer performances of various water-based nanofluids (NFs) relative to the base fluid in turbulent forced convection flow within a 2-D backward-facing step (BFS) channel with an upwardly deflected downstream wall with a uniform heat flux are analyzed using the package OpenFOAM. The k-ω shear stress transport (SST) model based on the Euler-Euler single-phase framework is used. The performance evaluation criterion (PEC) is defined to assess the relative importance of the enhanced heat transfer and intensified resistance (pressure drop) caused by Cu/water NFs and MWCNT-Fe3O4/water hybrid NFs (low concentration NFs), Fe3O4/water NFs, and Cu-MWCNT/water hybrid NFs (high concentration NFs). At Re = 30215, the maximum enhancement of the average Nusselt number (ANN) is 7% when the copper NPs are added to the water. In addition, the increment of the deflection angle from 0.0 to 1.27 enhances the ANN values by 44 ∼ 45% concerning low-concentration NFs. At Re = 7940, the friction factor increases by 24.3% and 32.1% when copper and MWCNT-Fe3O4 hybrid NPs are dispersed in the base fluid, respectively. The highest PEC value (1.07) is achieved when the copper NPs with ϕ = 0.003 are used in configuration BFS1 at Re = 7940. Using MWCNT-Fe3O4 hybrid NPs is only proposed at lower Re numbers when the downstream wall is deflected and ϕ = 0.001. At Re = 30215, due to the addition of magnetic NPs, the ANN value abates by 28.5% and 30.7%, respectively, in the canonical case and configuration BFS2. Among the high-concentration NFs, the highest PEC (1.05) is obtained using Cu-MWCNT hybrid NPs with ϕ = 0.01 at Re = 30215 when the downstream wall is deflected upwardly. As Mouromtseff (Mo) number-based figure-of-merit (FOM) verifies, the worst scenario (PEC < 1.0) is substituting the base fluid with Fe3O4/water NFs. Cu-MWCNT/water hybrid NFs with ϕ = 0.02 become an effective coolant (PEC > 1.0) when the deflection angle and Re number increase simultaneously.