This paper presents a three-dimensional numerical analysis to study the laminar heat transfer and flow characteristics of a flat tube equipped with a porous layer at the core of the tube at constant heat flux boundary condition. The flow regime and the wall boundary conditions are assumed laminar and with constant heat flux, respectively. The simulated results are compared with previously published data, and good agreement is observed. The effects of different parameters such as tube flattening, porous layer thickness, and porosity on the thermal–hydraulic performance of a flat tube are discussed in detail. Then, the performance efficiency for three parameters is evaluated. Numerical results show that the addition of a porous layer and flattening of the tube enhances the heat transfer and pressure loss of fluid in all cases, and the highest performance efficiency for the flattened tube with a porous layer is 1.89, which is obtained for the porosity of 0.1, porous thickness of 0.75, and internal height of 4 mm at a highest Re number of 1900.
