Experimental and numerical study of natural convection of Cu-water nanofluid in a cubic enclosure under constant and alternating magnetic fields

In this paper, experimental and numerical studies of natural convection heat transfer of Cu-water nanofluid in a cubic enclosure under the effects of both the time-unvarying and alternating magnetic fields are presented. The effect of the nanofluid volume fraction on the natural convection heat transfer in the presence of a constant magnetic field is studied for different Grashof numbers. Moreover, the influence of an alternating (in time) magnetic field in the shape of a rectangular wave with different frequencies on the heat transfer rate is investigated. The results show that in the absence of a magnetic field, adding Cu-nanoparticles to water enhances the heat transfer performance. The Nusselt number increases with increasing the volume fraction of the nanofluid. On the other hand, if the enclosure is subjected to a strong enough magnetic field, the negative effect of the elevated electrical conductivity by adding the nanoparticles dominates the effect of the increased thermal performance by using nanofluid. The increased electrical conductivity raises the magnetohydrodynamic effect, which acts against the buoyancy force. As a result, increasing the nanoparticles volume fraction reduces the heat transfer performance if the magnetic field strength is beyond a Hartmann number that is greater than a threshold value.