Influence of the shape of the inner boundary on thermomagnetic convection in the annulus between horizontal cylinders: Heat transfer enhancement

The paper studies convection in a horizontal annular gap filled with a magnetic fluid or gaseous oxygen under the influence of gravitational and magnetic forces. A current-carrying conductor and an external uniform magnetic field magnetizing an internal cylinder of a material with high magnetic permeability were considered as a source of a magnetic field. The influence of the shape of the inner cylinder and the magnitude of the magnetic field gradient on the heat transfer was studied. It is found that the strength of the magnetic field created by a current-carrying conductor is insufficient to compete with gravitational convection. In the absence of gravity, a variety of convective structures and the hysteretic nature of the transition between them were discovered. The shape of the conductor is an additional factor affected the convection. The effect of a high gradient magnetic field of a magnetizing inner cylinder on convection is studied too. In the case of magnetic fluid, this can ensure the excess of magnetic forces over gravitational by hundreds of times. Heat transfer in an external field with strength of 150 kA/m from a circular magnetized cylinder can be increased 3-4 times, and in a field of 1000 kA/m 4-6 times compared with natural gravitational convection. Heat transfer can be further enhanced by 40-50% by choosing the shape of the inner cylinder. The magnetic field can increase heat transfer through an annular gap filled with gaseous oxygen, 2 times.