Theoretical Study of Induction Pump for Molten Metal Using Rotating Twisted Magnetic Field

In this paper, the electromagnetic field in an induction pump for molten metal using rotating twisted magnetic field is theoretically analyzed. Asymptotic analysis for small magnetic Reynolds number clarifies that temporal mean value of the axial driving force f̅_z is almost uniform but rather small when the twist ratio ka₂ is considerably smaller than 1. On the other hand, when ka₂ is larger than 1, f̅_z near the outer boundary of the secondary conductor is large, whereas f̅_z around the central axis is very small. Such a nonuniform force is not suitable for driving fluids in the pump. Performance of the pump is estimated when the magnetic Reynolds number is always adjusted to a desired value by automatic control of frequency of power supply. The optimal value of the twist ratio ka₂ for the developed pressure is obtained. The ratio of the stator radius a₁ to the secondary-conductor radius a₂ has to be reduced to a value as small as possible in the hostile thermal environment by the molten metal. When the system is scaled up, the developed pressure is proportional to both a₂ and the axial length h of the stator. The estimation results give bases for designing the pump system and required specification of the power supply.