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Controlling the flow and heat transfer characteristics of conductive gases in circular tubes by means of applied magnetic fields is of great significance in various applications. However, the specific effects of magnetic fields with different orientations on these flow and heat transfer characteristics remain poorly understood. This paper addresses this issue by applying numerical calculations for evaluating the effect of magnetic fields (MFs) with different magnitudes defined according to the Hartmann number ( Ha) ranging from 0 to 740 and orientation, including transverse (TMFs), axial (AMFs), and radial (RMFs) on the flow and heat transfer characteristics of high-temperature conductive gas flows with Reynolds numbers ( Re) ranging from 9612 to 32 040. The results demonstrate that applied TMFs have anisotropic effects on the flow and heat transfer of conductive gases, while the effects of applied AMFs and RMFs are isotropic. Applied AMFs have little effect on the heat transfer characteristics of conductive gases, while applied TMF and RMF conditions suppress heat transfer at the tube wall, and the suppression effect of RMFs is stronger. Moreover, the heat transfer suppression effect of applied TMFs and RMFs first increases and then decreases with increasing Ha for a constant Re, and the value of Ha required to achieve the optimal heat transfer suppression effect increases with increasing Re. In addition, the transition gradient of the magnetic field directly outside of the applied magnetic field region causes the accumulation of Joule heat and therefore detracts significantly from the heat transfer suppression effect of TMFs and RMFs.

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