Magnetothermal force effect on natural convection through a partially-heated vertical channel

Abstract

Natural convection of a paramagnetic fluid through a partially-heated vertical channel is numerically studied in the presence of a magnetic field from two block magnets placed behind the heated wall. Magnets are aligned with opposite orientations. This magnet orientation induces strong magnetic force normal to the magnet at the magnet junction due to short distance between poles. When the temperature-dependent magnetic susceptibility changes due to wall heating near the magnet, the magnetothermal force is induced remarkably near the magnet junction. This additional force overlaps to the natural convection along the heated wall and results in the changes of heat and fluid flow along the heated wall. It is found that, flow becomes slow and the local heat transfer is suppressed below the elevation of the magnet junction, and the flow acceleration and heat transfer enhancement are observed above the junction elevation, of which effects depend on the relative magnet elevation to the heated wall. It is also found that the transition to vibrating flow occurs at the specific magnet elevation. The time-averaged Nusselt number suggests this vibrating convection has the potential to enhance the heat transfer remarkably because this magnetically-induced flow vibration continues along the heated wall up to the outlet.

Keywords

• natural convection
• paramagnetic fluid
• magnetic field
• magnetothermal force
• heat transfer enhancement/suppression
• vibrating flow