Measuring Flow Using a Permanent Magnet with a Large Constant Gradient
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Nuclear magnetic resonance (NMR) has long been used for measuring flows, as it has the unique advantage of being a truly non-invasive method by which to do so. In this paper, we describe our use of a magnet with a large constant gradient to measure two decades of average velocities (0.002–0.7 m/s), principally using a measurement method developed by Osan et al. that uses the initial decay of a Carr–Purcell–Meiboom–Gill sequence to determine the mean flow velocity. Thanks to the repeatability afforded by the stable gradient, we reliably pinpoint the transition to turbulence for pipe flow through the magnet.
The authors would like to acknowledge financial support from the Natural Sciences and Engineering Research Council (NSERC) of Canada through the Discovery Grants program (RGPIN-2017-04564). The technical help of the incomparable Brian Titus and the indefatigable Andrés Ramirez-Aguilera is gratefully acknowledged.