Influence of the magnetic field on Al2O3-Cu/H2O hybrid nanofluid natural convection in a square cavity with heat sources and internal heat generation/absorption

Abstract

In view of the growing interest in the numerical approach during the optimization phase of technical projects, this study proposes an in-depth analysis of the effects of several relevant parameters on the cooling of heat sources, part of the existing problems in the field of heat exchangers. The study focused on a natural convection problem inside a square cavity traversed by a vertical or horizontal magnetic field. This cavity contains four heating blocks, arranged at a uniform distance from each other and from the different surrounding walls. A hybrid nanofluid, composed of aluminum oxide (Al2O3) and copper (Cu) particles in equal proportions, was considered inside the cavity, imposing on it heat-generating or heat-absorbing behavior. The finite volume method was adopted as the solving approach for the adimensional governing equations, with the SIMPLE algorithm specifically chosen to handle the coupling between the momentum and continuity equations. Numerical results, covering a wide range of adimensional parameters such as Rayleigh number, Hartman number, volume fraction, internal heat value of the hybrid nanofluid, as well as for horizontal and vertical magnetic field orientations, have been grouped according to different scenarios to provide in-depth technical answers to fundamental questions related to the specific problem studied. These results have shown that increasing the flow regime leads to a transition from conductive to convective heat transfer, thus favoring an increase in heat exchange of up to 85% in certain scenarios. It is also clear that the cooling process of the heat sources is enhanced by the absorbing behavior of the hybrid nanofluid. Furthermore, the effects of the magnetic field (Ha) and the nanoparticle volume fraction (ϕ hnf) proved to be opposites: the former has an inhibiting effect, while the latter stimulates.