Performance enhancement of a Lorentz force velocimeter using a buoyancy-compensated magnet system

Abstract

Lorentz force velocimetry (LFV) is a highly feasible method for measuring flow rate in a pipe or a duct. This method has been established for liquid metal flows but also for electrolytes such as saltwater. A decrease in electrical conductivity of the medium causes a decrease of the Lorentz force which needs to be resolved, affecting the accuracy of the measurement. We use an electrical force compensation (EFC) balance for the determination of the tiny force signals in a test channel filled with electrolyte solution. It is used in a 90°-rotated orientation with a magnet system hanging vertically on its load bar. The thin coupling elements of its parallel guiding system limit the mass of the magnets to 1 kg. To overcome this restriction, which limits the magnetic flux density and hence the Lorentz forces, a weight force compensation mechanism is developed. Therefore, different methods such as air bearing are conceivable, but for the elimination of additional horizontal force components which would disturb the force signal, only compensation by lift force provided by buoyancy is reasonable. We present a swimming body setup that will allow larger magnet systems than before, because a large amount of the weight force will be compensated by this lift force. Thus the implementation of this concept has to be made with respect to hydrodynamical and mechanical stability. This is necessary to avoid overturning of the swimming body setup and to prevent inelastic deformation. Additionally, the issue will be presented and discussed whether thermal convection around the lifting body diminishes the signal-to-noise ratio (SNR) significantly or not.

Towards metering tap water by Lorentz force velocimetry

“…The magnet structures were preliminary chosen in such a way as to not exceed the mechanical limits of EMFC, because the gravity force causes unavoidable vertically directed mechanical stresses. To avoid this effect and to refine measurements further, a method can be applied to compensate the gravity force (see for example [30]).…”

Calibrationless rotating Lorentz-force flowmeters for low flow rate applications

“…Frictional losses within the WMB were investigated for different counter-weight masses. As shown in figure 4, increasing the mass of the counter-weight reduced the normal force between the spherical magnet and the ball bearing thereby reducing frictional losses, as predicted by equations (7) and (8). The deceleration curves shown in figure 4 were measured for different counter-weight masses while the RLFF was positioned away from the liquid-metal or any other external conductive or magnetic materials (τ L = 0).…”

“…To avoid this issue, researchers have developed a variety of non-rotating Lorentz force flowmeters that can be used for a wide range of fluids and flow rates [8][9][10][11]. However, all of these flowmeters require calibration involving either analytical and/or numerical modeling [12][13][14], external calibration equipment [15,16], or redundant flowmeters [4,17].…”

Lorentz force velocimetry using a bulk HTS magnet system: proof-of-concept

“…Hence, even in early works on LFV [11][12][13][14]18], the prospective idea to employ bulk HTS magnets has been proposed, because of their ability to act as much stronger trapped field magnets. Record trapped fields over 17 T using field cooling (FC) magnetisation was achieved in [19,20], whilst a maximum trapped field over 5 T was reported in [21] using compact and fast pulsed field magnetisation.…”