Numerical study on permanent magnetic heat transfer inside a dual semicircle enclosure: Controlling by magnet position

Abstract

Cooling is vital in electronic devices from which excess heat should be removed. Heat transfer can be controlled in this context through the dispersion of magnetic nanoparticles in the working fluid and subjecting it to an external magnetic field. Such a field can be obtained effectively and passively with permanent magnets. The resulting phenomenon is called thermomagnetic convection. The present study is dedicated to the numerical analysis of the heat transfer of a ferrofluid in a compact circular cavity subjected to two permanent magnets to assess the impact of the magnets' location and magnetic convection properties on the heat transfer behavior of the ferrofluid. The various equations governing the thermomagnetic in the enclosure are developed and presented in the non-dimensional form. The finite element method using Comsol Multiphysics is employed to model the problem. The effects of magnetic Rayleigh number, temperature factor, thermomagnetic number, and the position of the permanent magnets on the thermal and hydrodynamic response of the ferrofluid are investigated. It is found that the magnetic Rayleigh number and the temperature factor are the main parameters affecting the intensity of the heat transfer in the enclosure. The magnets' orientation affects the ferrofluid's thermal behavior mainly when the magnetic Rayleigh number is high. In that case, up to 64% rise in the average Nusselt number is reached when the inclination angle of the magnetic field is reduced from 75° to 15°. The impact of raising the magnetic Rayleigh number is also more important for lower inclination angle. Increasing this number from 5e3 to 5e7 leads to an augmentation of 91% and 11%, for the angles 15° and 75°, respectively Finally, multiplying the temperature ratio by 5 can increase the average Nusselt number by 2.