page_title: Lorentz force velocimetry
section_title: Conceptual setups
hierarchical_section_title: Lorentz force velocimetry / Conceptual setups
caption_attribution_description: English: Rotary LFV
context_page_description: Lorentz force velocimetry is a noncontact electromagnetic flow measurement technique. LFV is particularly suited for the measurement of velocities in liquid metals like steel or aluminium and is currently under development for metallurgical applications.The measurement of flow velocities in hot and aggressive liquids such as liquid aluminium and molten glass constitutes one of the grand challenges of industrial fluid mechanics. Apart from liquids, LFV can also be used to measure the velocity of solid materials as well as for detection of micro-defects in their structures.
  A Lorentz force velocimetry system is called Lorentz force flowmeter. A LFF measures the integrated or bulk Lorentz force resulting from the interaction between a liquid metal in motion and an applied magnetic field. In this case the characteristic length of the magnetic field is of the same order of magnitude as the dimensions of the channel. It must be addressed that in the case where localized magnetic fields are used, it is possible to perform local velocity measurements and thus the term Lorentz force velocimeter is used.
context_section_description: Lorentz force flowmeters are usually classified in several main conceptual setups. Some of them designed as static flowmeters where the magnet system is at rest and one measures the force acting on it. Alternatively, they can be designed as rotary flowmeters where the magnets are arranged on a rotating wheel and the spinning velocity is a measure of the flow velocity. Obviously, the force acting on a Lorentz force flowmeter depends both on the velocity distribution and on the shape of the magnet system. This classification depends on the relative direction of the magnetic field that is being applied respect to the direction of the flow. In Figure 3 one can distinguish diagrams of the longitudinal and the transverse Lorentz force flowmeters.
  It is important to mention that even that in figures only a coil or a magnet are sketched, the principle holds for both.
  Rotary LFF consists of a freely rotating permanent magnet (or an array of magnets mounted on a flywheel as shown in figure 4), which is magnetized perpendicularly to the axle it is mounted on. When such a system is placed close to a duct carrying an electrically conducting fluid flow, it rotates so that the driving torque due to the eddy currents induced by the flow is balanced by the braking torque induced by the rotation itself. The equilibrium rotation rate  varies directly with the flow velocity and inversely with the distance between the magnet and the duct. In this case it is possible to measure either the torque on the magnet system or the angular velocity at which the wheel spins.
caption: Fig. 4 : A simplified sketch of the rotary LFV. Adapted from.[1]
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