The effects of Rayleigh number, thermal conductivity ratio, thermal viscosity, Brownian motion, thermophoresis, and thickness and positions of the triangular blocks on nanofluid flow and heat transfer, are investigated. Results show that triangular blocks enhance the heat transfer rate when they are not placed in the reverse position. In addition, the average Nusselt number increases when the thermal conductivity ratio decreases. [PERSON] et al. [9] implemented the Lattice Boltzman Method in order to numerically investigate the interaction between Al\({}_{2}\)O\({}_{3}\)-Water nanofluid thermal radiation and free convection in a 2D shallow cavity. The effects of emissivity and Rayleigh number on nanofluid flow and radiated/free convection heat transfer are investigated. Results show that the Nusselt number of the total radiation and free convection heat transfer increases when the Rayleigh number and the emissivity increase. Thus, the coupling between radiation and free convection affects the flow and enhances the Nusselt number. [PERSON] et al. [10] implemented the Lattice Boltzman Method in order to numerically investigate the free convection within a 3D porous cavity with hot sphere obstacles, subjected to Lorenz forces and filled with Al\({}_{2}\)O\({}_{3}\)-Water nanofluid. The effects of Darcy number, Hartmann number, and Rayleigh number on the nanofluid heat transfer were evaluated. Results show that Lorenz forces enhance conduction at the expense of convection. [PERSON] et al. [11] experimentally investigated the heat transfer enhancement within a thermosyphon exploiting TiO\({}_{2}\)-Water nanofluid natural convection. The effects of heat input, inclination angle, and TiO\({}_{2}\) nanoparticles concentration on heat transfer (thermosyphon cooling) are studied and compared to the heat transfer carried out when using simple deionized water. Results show that the use of nanofluids reduces the wall temperature distribution and the thermosyphon thermal resistance. Thus, the performance of thermosyphon cooling is enhanced. [PERSON] et al. [12] numerically investigated the natural convection within the Al\({}_{2}\)O\({}_{3}\)-Water nanofluid filled in a circular enclosure that contains two horizontal cylinders. The effects of nanoparticle loading percentage and Rayleigh number on heat transfer are investigated. Results show that the heat transfer is enhanced for high nanoparticles concentration. The average Nusselt number increases when Rayleigh number increases. Thus, the use of alumina nanofluid gives much better heat transfer than the use of pure water. [PERSON] et al. [13] carried out a numerical comparison investigation about heat transfer by natural convection within a U-shaped enclosure, filled with Cu-Water and Al\({}_{2}\)O\({}_{3}\)-Water nanofluids. The effects of natural convection and geometric parameter on average Nusselt number are studied. The influence of Rayleigh number on the heat transfer within Al\({}_{2}\)O\({}_{3}\)-Water nanofluid is investigated. Results show that the heat transfer is improved when nanoparticle volume fraction and Rayleigh number increase and when the cooled wall length is extended. This work aims to numerically investigate the flow and the heat transfer within a specific rectangular enclosure, filled with Fe\({}_{3}\)O\({}_{4}\)-Water nanofluid. The specificity of the enclosure lies in the fact that it has a finned absorber plate, as a top wall, heated by solar energy. The fins below the absorber plate permit to enhance the heat transfer towards the nanofluid. The effects of Rayleigh number, enclosure inclination angle and fins height on nanofluid flow and heat transfer are studied. Section 2 of this article states and explains the problem in detail. The mathematical model that governs the hydrodynamic nanofluid problem as well as its dimensionless form is elaborated in Section 3. The numerical approach and validation are presented in Section 4. Section 5 presents numerical simulation results as well as their interpretation. Section 6 concludes the main findings of this work.