Lorentz force velocimetry
Lorentz force velocimetry (abbreviated LCA) is a non-contact electromagnetic flow measurement method for electrically conductive fluids. The Lorentz force velocimetry is particularly suitable for flow measurements in liquid metals and is therefore being investigated for their applicability in the aluminum and steel industries. A Lorentz force Anemometriesystem is also called the Lorentz force anemometer.
Principle
The basic principle of Lorentz force velocimetry is shown in the figure. Moving an electrically conductive fluid such as liquid aluminum in a tube under the influence of a magnetic field generated by a permanent magnet, so the eddy currents are generated in the fluid. They induce an electromagnetic force, the Lorentz force, which counteracts the movement of the fluid. According to the third Newtonian law " force = counter-force " ( actio = reactio ) affects an equally strong but opposite force on the permanent magnet. This force is proportional to the average speed, and the electrical conductivity of the fluid. By measuring this force, it is possible to determine the flow velocity of the fluid.
Liquid metals and electrolytes are paramagnetic or diamagnetic and therefore are attracted or repelled by a permanent magnet only in extremely small extent. The emergence of the LKA used Lorentz force has thus nothing to do with classical magnetic attraction or repulsion forces. It is solely due to eddy currents, whose strength depends on the electrical conductivity, the speed of movement and the amplitude of the magnetic field.
History
The Lorentz force velocimetry was invented by the English physicist Arthur Shercliff in the 1950s. However, it took several decades of no practical use. Only with the development of efficient permanent magnet systems, precise power measurement methods and special simulation software, it has become possible to perform this technology to industrial maturity. Currently Lorentz force anemometer for applications to be developed in metallurgy and are on the threshold for the market.