Bernd Halbedel

A universal noncontact flowmeter for liquids

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.

Flow rate measurement of weakly conducting fluids using Lorentz force velocimetry

We present a novel application of a contactless flow measurement system and validate its feasibility on an electrolyte pipe flow. The device relies on the technique of Lorentz force velocimetry (LFV). LFV operates without any contact to either the fluid or the surrounding pipe walls. This is advantageous if the fluid under consideration is hot and aggressive, like a glass melt for example. Glass melts, however, have a very low electrical conductivity, resulting in Lorentz forces in the micronewton range. In order to resolve these tiny forces, we developed a measurement system based on the principle of deflection. Experiments on an electrolyte flow with an electrical conductivity of less than 20 S m −1 prove to be successful and to agree well with numerical simulations, and therefore show for the first time the applicability of LFV for fluids of such low conductivities.

Optimization of NdFeB Magnet Arrays for Improvement of Lorentz Force Velocimetry

This paper presents the design and optimization process of magnet systems for the application in so called “Lorentz Force Velocimetry”. Here weight limitations, physical principle and systematical specifications give rise to a complete new combination of restrictions for the magnetic system design. Beneath the Lorentz force velocimetry background, the paper presents the idea using halbach arrays in combination with cladding technique to improve the currently used magnet systems significant. The magnet systems are geometrically optimized onto the physical principle using finite element simulations. These optimizations are presented on a state of the art reference design for Lorentz force velocimetry in electrolytic flows.

Numerical optimization of the magnet system for the Lorentz Force Velocimetry of electrolytes

Lorentz Force Velocimetry is a contactless method for the flow rate measurement of electrically conducting fluids. Thismethodisbasedontheinteractionofthefluidflowwiththetransversalpermanentmagneticfield. Theequalelectromagnetic force acts on the fluid and on the magnet system. The flow rate can be determined by measuring of this electromagnetic force. The magnet system has been optimized to achieve maximal sensitivity at a given magnet system weight. The sensitivity was defined as the ratio between the Lorentz force and the magnet system weight. The numerical model was developed using COMSOL Multiphysics. Validation and verification of the numerical model has been performed. The magnet system was optimized using the optimization toolbox in MATLAB.

High-precision horizontally directed force measurements for high dead loads based on a differential electromagnetic force compensation system

In this paper, we present an application for realizing high-precision horizontally directed force measurements in the order of several tens of nN in combination with high dead loads of about 10 N. The set-up is developed on the basis of two identical state-of-the-art electromagnetic force compensation (EMFC) high precision balances. The measurement resolution of horizontally directed single-axis quasi-dynamic forces is 20 nN over the working range of ±100 μN. The set-up operates in two different measurement modes: in the open-loop mode the mechanical deflection of the proportional lever is an indication of the acting force, whereas in the closed-loop mode it is the applied electric current to the coil inside the EMFC balance that compensates deflection of the lever to the offset zero position. The estimated loading frequency (cutoff frequency) of the set-up in the open-loop mode is about 0.18 Hz, in the closed-loop mode it is 0.7 Hz. One of the practical applications that the set-up is suitable for is the flow rate measurements of low electrically conducting electrolytes by applying the contactless technique of Lorentz force velocimetry. Based on a previously developed set-up which uses a single EMFC balance, experimental, theoretical and numerical analyses of the thermo-mechanical properties of the supporting structure are presented.

Towards metering tap water by Lorentz force velocimetry

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 Sm−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 ms−1 and conductivities ranging from 0.06 to 10 Sm−1.

Influence of the flow profile to Lorentz force velocimetry for weakly conducting fluids-an experimental validation

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.

Research data supporting [Lorentz Force Velocimetry using a bulk HTS magnet system: proof-of-concept]

Research data supporting [Lorentz Force Velocimetry using a bulk HTS magnet system: proof-of-concept]

Entrapment of Hard Particles into Cr(VI)-Free Conversion Layers of Electrodeposited Zinc Coatings to Improve Corrosion Resistance

Due to the restriction of passive layers containing Cr6+ [1], which were characterized by excellent corrosion protection due to their self-healing effect for scratches on metal surfaces, current corrosion protection systems consist of chromium (III) -containing thick layer passivation. Due to their lower hardness, current corrosion protection systems are susceptible to mechanical stress. This is particularly critical at barrel plating of screws, rivets etc. where the manufacturing process leads to damages of the corrosion protection layer and consequently to reduced corrosion resistance.To counter this problem, we point out one approach to install hard particles into the passivation layer. The entrapment of the hard particles into the passivation is detected by Glow Discharge Optical Emission Spectrometry. Comparative investigations in the corrosion chamber prove the improvement of the corrosion protection of steel parts with passivation layers containing hard particles.

Structure and superconducting characteristics of magnesium diboride, substitution of boron atoms by oxygen and carbon

An x-ray analysis of MgB2-based materials shows that they contain MgB2 and MgO phases. According to a quantitative Auger analysis (taken after removing the oxidized surface layer by Ar ion etching in the microscope chamber) the MgB2 phase contains some amount of oxygen that approximately corresponds to the composition MgB2.2-1.7O0.4-0.6. Rietveld refinement of the MgB2 phase, based on EDX data with varying B/O content, leads to the composition MgB1.68-1.8O0.2-0.32. Ab-initio modelling of boron substitution by oxygen in MgB2 (ΔH f = −150.6 meV/atom) shows that this is energetically favourable up to the composition MgB1.75O0.25 (ΔH f = −191.4 meV/atom). In contrast to carbon substitution, where very small levels of doping can dramatically affect the superconducting characteristics of the material with concomitant changes in the electron density, oxygen substitution results in very little change in the superconducting properties of MgB2. The formation of vacancies at the Mg site of both MgB2 and substituted MgB1.75O0.25 was modelled as well, but has shown that such processes are energetically disadvantageous (ΔHf of Mg0.875B2 and Mg0.75B1.75O0.25 are equal to −45.5 and −93.5 meV/atom, respectively).