Numerical study of viscous dissipation and non-Boussinesq model effects on CMC–TiO 2 fluid flow over backward facing step with baffle

The present work examined numerically the mixed convection of a non-Newtonian nanofluid flow through backward facing step with baffle. The Boussinesq and non-Boussinesq models are used to formulate the momentum equation, and the viscous dissipation is taken into account in the energy equation. The governing equations are discretized using the finite volume method. Effects of different key parameters such as Richardson number, temperature–viscosity coefficient, Brinkman number and power law index on both the heat transfer and the fluid flow characteristics are investigated. The results are presented in term of streamlines and isotherms contours as well as the average Nusselt number. The results show that both viscous dissipation and buoyancy forces affect greatly the flow and heat transfer structures. A multicellular zone is observed behind the step when considering the non-Boussinesq approximation for Ri ≥ 5 and taking into account viscous dissipation ( Br = 0.5). In addition, the flow behavior for both Boussinesq and non-Boussinesq approximations is identical for Ri = 1 and totally different for Ri ≥ 5. Furthermore, in contrast of the non-Boussinesq approximation, considering the Boussinesq one overestimates the heat transfer rate, especially for low power law index values.