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 ka
₂
is considerably smaller than 1. On the other hand, when ka
₂
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 ka
₂
for the developed pressure is obtained. The ratio of the stator radius a
₁
to the secondary-conductor radius a
₂
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 a
₂
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.