Publikationen

This paper investigates the interaction of an initially uniform magnetic field with an electrically conducting slab that moves perpendicularly to the magnetic field with arbitrary time-dependent velocity. It is demonstrated that the problem of determining the time-dependent Lorentz force and the time-dependent Joule heat in the slab is mathematically equivalent to solving a 1-D heat diffusion problem with time-dependent boundary conditions and to submitting the solution to a nonstandard postprocessing procedure. For the particular case of an impulsively driven slab we exploit the mathematical analogy between magnetic diffusion and heat diffusion by translating a textbook solution of the corresponding heat-transfer problem into exact and previously unknown relations for Lorentz force and Joule heat. Moreover, we use a 1-D finite-difference code to investigate more general time dependencies of the velocity including smooth accelerations and random velocity changes. Our numerical determination of reaction times (T98) of the Lorentz force in the case of smooth accelerations provides a useful design tool for the development of Lorentz force flowmeters with short reaction times.

Lorentz force velocimetry (LFV) is a contactless velocity measurement technique suited for electrical conductive fluids like liquid metals. This technique is based on the interaction of the melt flow with an externally applied magnetic field produced by a special arrangement of permanent magnets. These interactions result in the generation of a flow-breaking Lorentz force inside the melt which is proportional to the velocity of the flow. In the case of local Lorentz force velocimetry, the permanent magnet system is significantly small compared to the melt volume giving access to local velocity information.

Lorentz force velocimetry (LFV) is based on the electromagnetic induction of braking force acting on an electrically conductive fluid, which moves through a static magnetic field. Two such methods are presented here. First, time-of-flight LFV allows determining the flow rate of liquid metal by two flow meters placed at a predetermined distance by finding the time delay between their signals. Secondly, Lorentz torque velocimetry is a technique, which uses an electromagnetic pump with a torque sensor connected to the pump's shaft. Simultaneous pumping and measurement of the torque allows controlling the flow rate.