|
Lorentz force velocimetry〔 (LFV) 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 aluminum 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 (LFF). 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. == Introduction== The use of magnetic fields in flow measurement date back to 19th century, when in 1832 Michael Faraday attempted to determine the velocity of the River Thames. Faraday applied a method in which a flow (the river flow) is exposed to a magnetic field (earth magnetic field) and the induced voltage is measured using two electrodes across the same flow. This method is the basis of the one of most successful commercial application in flow metering known as the inductive flowmeter. The theory of such devices has been developed and comprehensively summarized by Prof. J. A. Shercliff〔Arthur J. Shercliff: ''Theory of Electromagnetic Flow Measurement''. Cambridge University Press, ISBN 978-0-521-33554-6.〕 in early 1950s. While inductive flowmeters are widely used for flow measurement in fluids at room temperatures such as beverages, chemicals and waste water, they are not suited for flow measurement of media such as hot, aggressive or for local measurements where surrounding obstacles limit access to the channel or pipe. Since they require electrodes to be inserted into the fluid, their use is limited to applications at temperatures far below the melting points of practically relevant metals. The Lorentz force velocimetry was invented by the A. Shercliff. However, it did not find practical application in these early years up until recent technical advances; in manufacturing of rare earth and non rare-earth strong permanent magnets, accurate force measurement techniques, multiphysical process simulation software for magnetohydrodynamic (MHD) problems that this principle could be turned into a feasible working flow measurement technique. LFV is currently being developed for applications in metallurgy〔Y. Kolesnikov, C. Karcher, A. Thess, "Lorentz Force Flowmeter for Liquid Aluminum: Laboratory Experiments and Plant Tests" (in German), ''Metall. Mat. Trans.'' B 42B (2011) pp. 241-250., doi:10.1007/s11663-011-9477-6〕 as well as in other areas.〔http://www.tu-ilmenau.de/lorentz-force/〕 Based on theory introduced by Shercliff there have been several attempts to develop flow measurement methods which do not require any mechanical contact with the fluid,.〔J. Priede, D. Buchenau., G. Gerbeth, "Contactless Electromagnetic Phase-Shift Flowmeter for Liquid Metals", ''Measur. Sci. Tech.'' 22 (2011) 055402,2011〕〔 Among them is the eddy current flowmeter which measures flow-induced changes in the electric impedance of coils interacting with the flow. More recently, a non-contact method was proposed in which a magnetic field is applied to the flow and the velocity is determined from measurements of flow-induced deformations of the applied magnetic field,.〔J. Baumgartl, A. Hubert, and G. M¨uller, "The use of magnetohydrodynamic effects to investigate fluid flow in electrically conducting melts", ''Phys. Fluids A'' 5, 3280 (1993)〕〔Stefani F., Gundrum T., Gerbeth G., "Contactless inductive flow tomography", ''Phys Rev E'' 70,056306 (2004)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lorentz force velocimetry」の詳細全文を読む スポンサード リンク
|