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Schematic of the noncontact Lorentz force flowmeter used in the experiments: (a) A turbulent flow of salt water (with Reynolds numbers roughly between 3.2 × 104 and 1.3 × 105) is exposed to the magnetic field generated by a lightweight permanent-magnet system hanging on a four-wire pendulum. The displacement of the pendulum is measured using an interferometer as sketched in (b): 1 – He-Ne-Laser, 2 – beam splitter, 3 – reference corner cube reflector, 4 – photo detector, and 5 – measurement corner cube reflector.
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Results of measurements and simulations: Lorentz force as a function of the volumetric flow rate of salt water with electrical conductivities 2.3 S/m (red), 4.0 S/m (blue), and 6.2 S/m (green) as obtained from the experiments (symbols) and from numerical simulations of a steadily translating solid body (lines). The inset shows the experimental values of the calibration constant (dots) and the numerical value (horizontal line) as a function of the volume flux in litres per second. The calibration constant c is determined as an average over all shown measurements. For fixed volume flux, the Lorentz force is proportional to the electrical conductivity.
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Lorentz force velocimetry (LFV) is a noncontact electromagnetic flow measurement technique for liquid metals that is currently used in fundamental research and metallurgy. Up to now, the application of LFV was limited to the narrow class of liquids whose electrical conductivity is of the order 106 S/m. Here, we demonstrate that LFV can be applied to liquids with conductivities up to six orders of magnitude smaller than in liquid metals. We further argue that this range can be extended to 10−3 S/m under industrial and to 10−6 S/m under laboratory conditions making LFV applicable to most liquids of practical interest.
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