Development and fundamental characteristics of co-axial MHD energy conversion device

Abstract

Innovative electro-magnetic energy conversion device has been developed. This device has co-axial configuration with liquid metal filled inside under applied magnetic field. The azimuthal liquid metal flow is decelerated by Lorentz force acting as a body force. The rotational torque continuously increases with excessive kinetic energy converted into electric energy by increasing magnetic field. The static and dynamic characteristics of the device have experimentally investigated with AC servo-motor as a driving source. The experimental results show that the rotational torque can be controlled with electric power extraction by applied magnetic field and external load resistance. The liquid metal inside the device is driven in the azimuthal direction directly by the electrically insulated propeller on the shaft and the electric power is extracted with proportionally to the square of shaft rotational speed. The required rotational torque increases with applied magnetic flux density due to dominant eddy current induced by non-uniform magnetic field in azimuthal direction. The constant rotational speed can be maintained with power generation by controlling applied magnetic flux density even for increasing input torque. It was clarified that the time constant for the control of the rotational speed becomes smallest when the changing time of applied magnetic flux density and that of input torque are equal.