Combined convection of ferrofluids in a partitioned triangular cavity equipped with two permanent magnets

Various passive and active methods are employed to control heat transfer in various industries. The application of external magnetic fields and porous materials usage are among these methods. Understanding the interplay between magnetic and gravitational convection in porous media is therefore essential for such systems. In the present study, mixed magnetic-natural convection heat transfer through a dual porous enclosure filled by a ferrofluid is numerically investigated. Two permanent magnets are placed at two sides of the enclosure. The equations governing the flow and energy transfer in the cavity are derived in the non-dimensional form. Langevin equation is applied to computing the magnetization of the ferrofluid. The various equations are solved by means of the finite element method. The influence of key factors including buoyancy and magnetic Rayleigh numbers Ra and Ra_m, inclination angle of the enclosure, Darcy number and the porosity of the porous medium on the flow and thermal behaviors of the fluid are studied and discussed. It was found that enhancing the natural gravitational convection hinders the thermomagnetic convection in the top part of the enclosure. When the enclosure is tilted, the magnetic convection becomes less affected by the natural convection. An average of 28% increase in the heat transfer rate is found when the cavity is tilted vertically in comparison to a horizontal one. Raising Ra and Ra_m enhances the gravitational and magnetic convections, respectively. For high Ra, the heat transfer is maximum when the enclosure is inclined vertically, i.e. when the gravitational convective effects are minimized. The heat transfer rate can rise by up to 180% when strong magnetic effects are present compared to pure gravitational convection. The flow circulation is intensified when Da and ε are raised. Increasing ε reduces the overall heat transfer due to the inhibited impact of the porous medium. These outcomes can provide perspectives for heat transfer optimization and thermal management systems and inform the design of new components.