Thermal hydraulic characteristics of square ducts having porous material inserts near the duct wall or along the duct centre

•A new solver based on OpenFOAM is developed to solve porous media heat transfer.•For porous media attached near to the walls, heat transfer can be enhanced up to 65%.%•Increase in heat transfer rate for core side configuration is about 938%.%•There is a critical thickness of porous media for each of the porosity value.•Increasing porosity at the wall side increases Nu but for the core side, it deceases. In the present work, forced convective heat transfer and pressure drop in the entrance and fully developed regions of a square duct, which is partly filled by porous medium, is numerically investigated. The porous medium is placed (i) adjacent to the wall or (ii) at the core of the square duct. This 3D analysis was essential because in the earlier studies the thermal hydraulic characteristics were predicted by considering the flow to be between two parallel plates or as axisymmetric, which is not applicable for square ducts. Apart from the thickness of the porous medium, changes in porosity is also considered in the analysis. The porous medium is taken to be wire mesh screens, as it is the most common case. The flow through porous medium is modelled using Darcy–Forchheimer model and the heat transfer is modelled using local thermal equilibrium model. For solving this problem, a new solver is developed using the open source CFD package OpenFOAM. From the results it is observed that, adding porous inserts at the core of the duct provides better heat transfer rate with lesser pressure drop. The effect of porosity on heat transfer and pressure drop is accentuated only if the porous medium thickness ratio is greater than 0.625. The maximum heat transfer that can be achieved for wall side case when thickness ratios in the range 0.8-1.0 is approximately 1.65 times than that of a duct without porous medium. If the porous medium is at the core side case, maximum heat transfer is 10.4 times when the thickness ratio is between 0.85-0.95. It is also found that, when the porous medium is at the wall side, the Nusselt number increases with increases in porosity. However, if the porous medium is in the core side, the Nusselt number increases with decreasing porosity.