Numerical analysis on laminar forced convection improvement of hybrid nanofluid within a U-bend pipe in porous media

Nanofluids and porous media have offered a feasible approach to develop heat transfer within industrial systems. The application of porous substances with high thermal conductivity can enhance the heat transfer as well. Besides the heat transfer improvements, porous media are capable of enhancing the pressure drop. In this regard, the current research is aimed at conducting a 3D numerical investigation on the laminar flow and heat transfer of Al2O3-CuO- water hybrid nanofluid inside a U-bend pipe within a porous medium. The evaluations were performed for a wide range of governing parameters. ANSYS-FLUENT is a finite volume-based computational fluid dynamics (CFD) solver which was considered to discretize the governing equations. The line-by-line method was also applied for iterative solution of the algebraic equations. As well as, the nanofluid flow was employed as a two-phase flow where a Darcy-Brinkman-Forchheimer equation was exploited to model fluid flow within a porous medium. Simulations were carried out under the laminar flow regime using a finite volume scheme. Moreover, the thermal boundary conditions of the cylinder walls were constant uniform heat flux. The averaged Nusselt number, volume fraction (0%-5%), and the performance evaluation criteria (PEC) were assessed for a verity of Darcy and Dean numbers. The findings of the current work were compared with the experimental data and the simulation accuracy was verified due to the proper agreement between the theoretical and experimental results. Based on the results, Darcy number (10(-4)-10(-1)) and the porous thickness ratio enlargement could significantly affect the elevation of the heat transfer coefficient. Furthermore, for all nanofluids, the averaged Nusselt number and pressure drop exhibited an increasing pattern upon an increment of volume fraction while PEC showed a decreasing one. In addition, the maximum PEC was observed in configurations encompassing a permeable porous media (i.e. a medium with Da = 0.1 and r(P) = 0.8).