non-uniform magnetic field

The purpose of this paper is to investigate the heat transfer and entropy generated due to mixed convection of hybrid nanofluid inside the lid-driven semi-oval chamber. The magnetic field is applied uniformly and non-uniformly. The simulation is performed by MRT-LBM and by writing computer code in Fortran language. Effect of Richardson number (0.1, 1 and 10), nanoparticles volume fraction (0-0.06), Hartmann number (0-60), inclination angle of the chamber (-90, 0 and +90 degrees) and type of magnetic field applied (uniform and non-uniform) on the flow formed in the chamber is evaluated. The results show that increasing the volume fraction of nanoparticles increases the flow strength, average Nusselt number, total volumetric entropy and Bejan number and most of the effect is observed for Richardson number 10 and inclination angle +90°. In all cases, increasing the Hartmann number decreases maximum values of streamlines and heat transfer, and this effect decreases with increasing Richardson number. By applying a magnetic field non-uniformly, it can change the flow strength by more than 80% and increase the heat transfer to 35%. Increasing the Hartmann number makes the effect of the non-uniform magnetic field more obvious, and the heat transfer has the largest share in the total volumetric entropy.

In the present study, the entropy generated due to the conjugate heat transfer of the hybrid nanofluid inside the K-shaped chamber under magnetic field and uniform heat absorption/generation is investigated. The simulation was performed by writing computer code in Fortran language using the lattice Boltzmann method. Variations in Rayleigh number, volumetric fraction of nanoparticles, Hartmann number, heat absorption/generation coefficient, thermal conductivity ratio, chamber aspect ratio and type of magnetic field applied have been evaluated as the main variables of this study. The findings showed that the flow strength, heat transfer rate and entropy produced could be reduced by applying a magnetic field. A lower reduction of the average Nusselt number is achieved by non-uniform application of a magnetic field. Increasing the heat absorption/generation coefficient due to increasing the set temperature leads to decreasing the mean Nusselt number, which this influence increases with increasing the Hartmann number. Addition of nanoparticles to the base fluid in which the conduction of the phenomenon is predominant, increases the rate of heat transfer. Heat transfer is a function of the ratio of thermal conductivity and Rayleigh number that increasing these two parameters increases the convection effects, and in this case, the effect of increasing the Hartmann number is more pronounced. Increasing the chamber aspect ratio leads to a decline in the mean Nusselt number and entropy production, but the effect of adding nanoparticles is greater in this case. Entropy production decreases with increasing Hartmann number and increases with Rayleigh number and heat absorption/generation coefficient.