Research On Heat Transfer Characteristics Of Natural Convection Strengthened By Magnetic Field

Thermomagnetic convection is a widespread physical phenomenon in nature.In recent years,using magnetic fields to enhance the natural convection heat transfer of air has attracted the attention of many researchers.In order to study the influence of gradient magnetic field on the natural convection of air in closed square cavity,natural convection of air in porous media square cavity and natural convection of air near vertical plate,a mathematical model of magnetically induced natural convection was constructed and the corresponding finite element numerical calculation program was written in this paper.The influence of different factors on the natural convective heat transfer of three different spatial structures under magnetic field were analyzed,and the heat transfer characteristics of thermomagnetic convection of different spatial structures with or without gravity environment were compared.Main contents and research conclusions are as follows:(1)Heat transfer characteristics of thermomagnetic convection of air in a closed square cavity under magnetic field:The magnet located near the hot wall has a greatest impact on the natural convective heat transfer of air in the enclosed square cavity.Air velocity in the square cavity and the average Nusselt number increase with the increase of the magnet remanent flux density of the magnet.The thermomagnetic convection effect caused by the magnetic field under the zero gravity environment is stronger than that under the gravity environment.When Br=5 T,compared with pure heat conduction,the optimal position of the magnet is x=20 mm,and the average Nusselt number increases by 166.30%.Meanwhile,compared with pure gravity natural convection,the optimal position of the magnet is x=10 mm,and the average Nusselt number increases by 9.33%.(2)Heat transfer characteristics of thermomagnetic convection of air in a porous media square cavity under magnetic field:When a single group of magnets is located at x=20 mm under zero gravity environment and a single group of magnets is located at x=10 mm under gravity environment,the effect of thermomagnetic convection caused the magnetic field has a greatest impact.The average Nusselt number increases with the increase of the magnet remanent flux density of the magnet.The larger the Da number,the better the effect of air thermomagnetic convection.When Br=5 T,Da=10-2 and a single group of magnets is located at x=20mm,the average Nusselt number increased by 72.18%compared with pure heat conduction.When Br=5 T,Da=10-2 and a single group of magnets is located at x=20 mm,the average Nusselt number increases by 9.53%compared with pure gravity natural convection.(3)Heat transfer characteristics of thermomagnetic convection of air around vertical plate under magnetic field:When a single group of magnets is located at z=10 mm,the effect of thermomagnetic convection caused the magnetic field has a greatest impact.When Br<1 T,the average Nusselt number decreases with the increase of residual magnetic flux density.When Br>1 T,the average Nusselt number increases significantly with the increase of the magnet remanent flux density of the magnet.The convective heat dissipation capacity under the two groups of magnets is stronger than that under the single group of magnets.When Br=4 T and a single group of magnets is located at the lower end of the vertical plate,the average temperature of the vertical plate decreases by 8.58 ℃ and the average Nusselt number increases by 3.03%compared with pure gravity natural convection.Meanwhile,the average temperature of the vertical plate under the two groups of magnets decreased by 9.91℃ and the average Nusselt number increased by 3.54%.