Abstract
Magnetothermal free convection of air in a square enclosure under a nonuniform magnetic field provided by a permanent neodymium-iron-boron magnet is numerically studied. The natural convection under the gravity field alone is also studied for comparison. The physical fields of magnetizing force, velocity, and temperature as well as the local distribution characteristic of Nusselt number are all presented in this paper. The results show that the buoyancy convection of air in the square enclosure under magnetic field is quite different from that under the gravity field. The local value of Nusselt number under the magnetic field supplied by a permanent magnet with a residual magnetic flux density of about 4.5 Tesla can reach a high value of about three times larger than the maximum local value of Nusselt number under the gravity field. Relatively uniform distributions of temperature gradient and Nusselt number can be obtained along the cold wall of the enclosure under the magnetic field. A permanent magnet with high magnetic energy product withBrreaching to 3.5 Tesla can play a comparative role on the averaged Nusselt number compared with that under the gravity environment.
Highlights
The heat transfer and flow characteristics of natural convection in enclosures have attracted much research over the years due to their many practical engineering applications, such as in building insulation, growing crystals, solar energy collection, cooling of electrical industries, and flows in rooms due to thermal energy sources [1, 2]
The present study focuses on the heat transfer and flowing characteristic of the magnetothermal convection of air in a square enclosure driven by a permanent magnet field alone
The flow field, temperature field, and the distribution of local Nusselt number along the walls are obtained under the magnetic field with Br = 4.5 T; the difference of the effect of magnetic field and gravity field on natural convection is studied
Summary
The heat transfer and flow characteristics of natural convection in enclosures have attracted much research over the years due to their many practical engineering applications, such as in building insulation, growing crystals, solar energy collection, cooling of electrical industries, and flows in rooms due to thermal energy sources [1, 2]. Tagawa et al [12,13,14,15,16,17,18,19,20] carried out studies about the effects of magnetic fields on the natural convection These studies have shown experimentally and numerically how to enhance or suppress heat transfer by the application of a magnetic field supplied by superconducting magnet. The permanent magnet with large residual magnetic flux density can supply a nonuniform magnetic field and drive the gas free convection under a gradient temperature field. The present study focuses on the heat transfer and flowing characteristic of the magnetothermal convection of air in a square enclosure driven by a permanent magnet field alone. Comparison is carried out for the convection driven by magnetic field and gravity field, respectively
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