In this paper, we present enhanced flow rate measurement by applying the contactless Lorentz Force Velocimetry (LFV) technique. Particularly, we show that the LFV is a feasible technique for metering the flow rate of salt water in a rectangular channel. The measurements of the Lorentz forces as a function of the flow rate are presented for different electrical conductivities of the salt water. The smallest value of conductivity is achieved at 0.06 S•m −1 , which corresponds to the typical value of tap water. In comparison with previous results, the performance of LFV is improved by approximately 2 orders of magnitude by means of a high-precision differential force measurement setup. Furthermore, the sensitivity curve and the calibration factor of the flowmeter are provided based on extensive measurements for the flow velocities ranging from 0.2 to 2.5 m•s −1 and conductivities ranging from 0.06 to 10 S•m −1 .

The Lorentz force velocimetry (LFV) is a highly feasible contactless method for measuring flow rate in a pipe or in a channel. This method has been established for liquid metal flows but also for weakly conducting electrolytes where the Lorentz force amplitudes are typically six orders smaller than the ones from liquid metal flows. Due to an increased resolution of the Lorentz force measurements which was the main focus of research in the last years, now it is possible to investigate the influence of the flow profile on the amplitude of the Lorentz force. Even if there is a semi-theoretical approach an experimental validation is still outstanding. Therefore we have tested symmetric and asymmetric flow profiles to test the LFV for weakly conducting fluids for typical industrial flows. Salt water has been used as a test electrolyte with constant values of the electrical conductivity from 0.035 to 20 S m −1 and of the flow velocity in a range of 0.5-3 m s −1. We confirmed by extensive measurements that LFV is a suitable method for flow measurements even for different flow profiles within 5% measurement uncertainty. For a wide range of applications in research and industry the LFV should be not sensitive to various flow profiles.

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.

We demonstrate that a flow velocity measurement can be transformed into a non-invasive force measurement by metering the dragforce acting on a system of magnets that is arranged around a flow channel. This method is called Lorentzforce velocimetry and has been developed in the last years in our institute. It is a highly feasible principle for materials with large conductivity like liquid metals. To evolve this method for weakly conducting fluids like salt water or molten glass the dragforce measurement is the challenging bottleneck. Here forces of 10−8 and less of the weightforce of the magnet system have to be resolved in the rather noisy environment of the flow channel. In this paper different force measurement techniques get tested and compared. In the first setup the drag-force is acting on the magnets that are hanging as a pendulum with 0.5 m long wires on a mounting. Here the displacement in the range of a few μm can be detected with a laser interferometer and another optical positioning sensor. For the second setup the magnet system is attached to a state of the art electromagnetic force compensation balance. The balance is used in an unusual orientation: It is turned by 90 degrees to measure the horizontally acting Lorentzforce. Different ways of getting the correct force signal out of the two measurement setups will be presented and discussed. For generalization of the measurement principle the Lorentzforce is determined for different fluid profiles. In addition to that we have developed new systematic noise reduction methods to increase the resolution of both force measurement techniques by a factor of ten or larger which we will present here.