The change of bifurcating natural convection in a horizontal annulus by self-induced circular magnetic field

In this study, the natural convection in 2-D annulus that the circular magnetic field is being applied is numerically investigated. The concentric annulus composed of two isothermal horizontal circular cylinders is filled with a fluid of the Prandtl number 0.3. Under these conditions, the solution of the natural convection shows bifurcation phenomenon that is, dual solutions exist depending on its initial condition. Therefore the present thermal behavior of the system highly depends on its historical thermal record, i.e., the thermal hysteresis appears. How these phenomena change by magnetic fields has been investigated in this study. The intensity of the magnetic field is inversely proportional to the distance from the annulus. The numerical simulation of the natural convection in the annulus was carried out for different Rayleigh and Hartmann numbers. As the intensity of the magnetic field increases, the flow is suppressed by the electromagnetic body force, the heat transfer rate decreases. Finally, the local equivalent conductivity at the surface of both inner and outer cylinders becomes unity. It was found that the bandwidth of Rayleigh number in which the thermal bifurcation occurs is rapidly narrowed by increasing the magnetic field intensity. The thermal hysteresis was completely disappeared at the Hartmann number over 20.