This article provides a numerical study on carbon nanotube–water nanofluid convection in a three-dimensional cavity under a magnetic field effect. Two walls are kept at a hot temperature, and the upper and lower horizontal walls are considered adiabatic. As a new configuration, the beneficial effect of using a nanofluid is coupled with the incorporation of cold V-shape obstacle placed in the cubic cavity; in addition, an external magnetic field is applied toward the horizontal x -axis direction. The finite element method based on the Galerkin’s Weighted Residual technique is used to solve the three-dimensional governing equations. In this paper, the ranges of the parameters used are the Hartmann number, varied from 0 to 100, Rayleigh number from 10 3 to 10 5 , nanofluid volume fraction between 0% and 4.5%, and the body V-shaped opening angle varied from 0 to 80°. The effect of the obstacle shape and the added nanoparticle concentration on the flow behaviors, the different instabilities generated, and the heat transfer exchanged were exposed. An enhancement in heat transfer was recorded by increasing the obstacle opening angle and the volume fraction of the carbon nanotubes. Special attention has also been devoted to the calculation of the different kinds of entropy generations.

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