LorentzLorentzLorentzLorentz ForceForceForceForce VelocimetryVelocimetryVelocimetryVelocimetry forforforfor PoorlyPoorlyPoorlyPoorly ConductingConductingConductingConducting FluidsFluidsFluidsFluids ----

DevelopmentDevelopmentDevelopmentDevelopment andandandand ValidationValidationValidationValidation ofofofof aaaa NovelNovelNovelNovel

FlowFlowFlowFlow RateRateRateRate MeasurementMeasurementMeasurementMeasurement DeviceDeviceDeviceDevice

WEGFRASS,WEGFRASS,WEGFRASS,WEGFRASS,AndreAndreAndreAndre1111;;;; RESAGK,RESAGK,RESAGK,RESAGK, ChristianChristianChristianChristian1111;;;; DIETHOLD,DIETHOLD,DIETHOLD,DIETHOLD, ChristianChristianChristianChristian2222;;;;FRFRFRFRÖÖÖÖHLICH,HLICH,HLICH,HLICH, ThomasThomasThomasThomas2222;;;; WERNER,WERNER,WERNER,WERNER, MichaelMichaelMichaelMichael3333;;;; HALBEDEL,HALBEDEL,HALBEDEL,HALBEDEL, BerndBerndBerndBernd3333;;;;

THESS,THESS,THESS,THESS,AndrAndrAndrAndréééé1111(1Institute of Thermodynamics and Fluid Mechanics

2Institute of Process Measurement and Sensor Technology3Institute of Inorganic-nonmetallic Materials

Department of Mechanical Engineering, Ilmenau University of Technology,

P.O. Box 100565, 98684 Ilmenau, Germany)

Abstract: TheTheTheThe paperpaperpaperpaper demonstrateddemonstrateddemonstrateddemonstrated thethethethe feasibilityfeasibilityfeasibilityfeasibility ofofofof LorentzLorentzLorentzLorentz ForceForceForceForce VelocimetryVelocimetryVelocimetryVelocimetry forforforfor flowflowflowflow raterateraterate measurementsmeasurementsmeasurementsmeasurements ofofofof

weaklyweaklyweaklyweakly conductingconductingconductingconducting electrolyteselectrolyteselectrolyteselectrolytes usingusingusingusing experimentalexperimentalexperimentalexperimental resultsresultsresultsresults onononon saltsaltsaltsalt waterwaterwaterwater flowflowflowflow exposedexposedexposedexposed totototo aaaa permanentpermanentpermanentpermanent magnetmagnetmagnetmagnet

system.system.system.system. ThisThisThisThis innovativeinnovativeinnovativeinnovative flowflowflowflow measurementmeasurementmeasurementmeasurement techniquetechniquetechniquetechnique allowsallowsallowsallows thethethethe non-contactnon-contactnon-contactnon-contact determinationdeterminationdeterminationdetermination ofofofof flowflowflowflow ratesratesratesrates andandandand

reliesreliesreliesrelies onononon thethethethe interactioninteractioninteractioninteraction betweenbetweenbetweenbetween aaaa magneticmagneticmagneticmagnetic fieldfieldfieldfield andandandand aaaa movingmovingmovingmoving conductingconductingconductingconducting fluid.fluid.fluid.fluid. WhenWhenWhenWhen anananan electricallyelectricallyelectricallyelectrically

conductingconductingconductingconducting fluidfluidfluidfluid movesmovesmovesmoves throughthroughthroughthrough thethethethe magneticmagneticmagneticmagnetic fieldfieldfieldfield aaaa LorentzLorentzLorentzLorentz forceforceforceforce isisisis generatedgeneratedgeneratedgenerated andandandand actsactsactsacts onononon thethethethe measurementmeasurementmeasurementmeasurement

system.system.system.system. TheTheTheThe presentpresentpresentpresent reportreportreportreport providesprovidesprovidesprovides anananan overviewoverviewoverviewoverview aboutaboutaboutabout thethethethe experimentalexperimentalexperimentalexperimental setupssetupssetupssetups andandandand thethethethe firstfirstfirstfirst measurementmeasurementmeasurementmeasurement

results.results.results.results.

Key words:::: LorentzLorentzLorentzLorentz forceforceforceforce velocimetry;velocimetry;velocimetry;velocimetry; flowflowflowflow measurement;measurement;measurement;measurement; electrolytes;electrolytes;electrolytes;electrolytes; non-contactnon-contactnon-contactnon-contact measurementmeasurementmeasurementmeasurement

1111 IntroductionIntroductionIntroductionIntroduction andandandandMotivationMotivationMotivationMotivation

There are several well-known techniques available to accomplish the various required flow measurementtasks in industry. But in some special applications the fluids are extremely hot, corrosive or abrasive andclassical methods would not withstand the rough environment for a sufficiently long time, because the sensor ineach of these techniques interacts with the surrounding fluid or with the pipe wall. Examples for these fluidsinclude metal melts and acids. In order to avoid these interactions a novel contact-free flow rate measurementdevice has been developed, the so-called Lorentz force flowmeter (LFF).

The basic idea of the measurement device relies on the interaction between a magnetic field and a movingconducting fluid. When an electrically conducting fluid moves through the magnetic field, a Lorentz force isgenerated that acts on the measurement system. The higher the electrical conductivity of the fluid, the higherthe generated Lorentz force, and in turn the higher the force acting on the measurement device. So far, thismethod has been studied [1] [2] and verified [3] only for molten metals, as they have a conveniently highelectrical conductivity of several MSm-1, and is known as Lorentz force velocimetry (LFV).

TheTheTheThe workworkworkwork ofofofof ourourourour groupgroupgroupgroup extendsextendsextendsextends thethethethe knownknownknownknown LFFLFFLFFLFF forforforfor moltenmoltenmoltenmolten metalsmetalsmetalsmetals totototo anananan LFFLFFLFFLFF thatthatthatthat isisisis capablecapablecapablecapable ofofofofresolvingresolvingresolvingresolving thethethethe tinytinytinytiny LorentzLorentzLorentzLorentz forcesforcesforcesforces involvedinvolvedinvolvedinvolved inininin thethethethe flowmeteringflowmeteringflowmeteringflowmetering ofofofof poorlypoorlypoorlypoorly conductingconductingconductingconducting electrolytes.electrolytes.electrolytes.electrolytes. InInInIn thethethethecoursecoursecoursecourse ofofofof thethethethe projectprojectprojectproject work,work,work,work, twotwotwotwo differentdifferentdifferentdifferent testtesttesttest facilitiesfacilitiesfacilitiesfacilities havehavehavehave beenbeenbeenbeen built.built.built.built. BothBothBothBoth facilitiesfacilitiesfacilitiesfacilities useuseuseuse saltsaltsaltsalt waterwaterwaterwater asasasas thethethethe

weaklyweaklyweaklyweakly conductingconductingconductingconducting modelmodelmodelmodel fluid.fluid.fluid.fluid.

2222 ExperimentExperimentExperimentExperiment andandandand ResultsResultsResultsResults

The two facilities mentioned in the previous section can be distinguished by their means of forcemeasurement; the preliminary setup uses the displacement of a pendulum (1) for detecting the Lorentz force,the final setup uses electromagnetic force compensation (2). Both principles will be explained in the following.

(1)(1)(1)(1) PendulumPendulumPendulumPendulum SetupSetupSetupSetup

Fig.Fig.Fig.Fig. 1111:::: SketchSketchSketchSketch ofofofof thethethethe pendulumpendulumpendulumpendulum setup.setup.setup.setup. TheTheTheThe mainmainmainmain componentscomponentscomponentscomponents areareareare thethethethe pendulumpendulumpendulumpendulum comprisingcomprisingcomprisingcomprising thethethethe magnetmagnetmagnetmagnet systemsystemsystemsystem (1),(1),(1),(1), thethethethe

interferometricinterferometricinterferometricinterferometric deflectiondeflectiondeflectiondeflection measurementmeasurementmeasurementmeasurement devicedevicedevicedevice (2),(2),(2),(2), andandandand thethethethe electrolyteelectrolyteelectrolyteelectrolyte channelchannelchannelchannel ofofofof rectangularrectangularrectangularrectangular cross-sectioncross-sectioncross-sectioncross-section (3).(3).(3).(3).

To prove the applicability of LFV to weakly conducting fluids, we perform experiments on the setuppresented in Fig. 1 that contains salt water with an electrical conductivity in the range of 2.3 Sm-1 to 14 Sm-1 atroom temperature. Here, the measurement system based on the principle of deflection. The fluid flows in a ductwith rectangular cross-section (30 mm x 50 mm), whose design is based on the numerical results of Werner etal. [4].The flow velocities are in the range of up to 4 ms-1.

In order to generate a high magnetic field strength, we apply a magnet system which is equipped withhigh-energy magnets made of NdFeB. The magnet system is suspended on thin tungsten wires resembling apendulum and the entire system is mounted on a frame of aluminium profiles.

The generated Lorentz force causes a deflection of the magnet system which is detected with a laserinterferometer. Both the aluminium frame and the laser interferometer are mounted on a granite block with amass of about 400 kg in order to suppress vibrations from the environment. The Lorentz force is calculatedfrom the dimensions of the pendulum and the measured average deflection [5] (Fig. 2). The mentionedelements above are crucial for measuring the Lorentz force which is expected to be in the range ofFLorentz ≤ 10-5 N [4] from numerical simulations. In order to evaluate the sensitivity of LFF, we performexperiments at various fluid velocities and for five different electrical conductivities of 2.3 Sm-1, 6.5 Sm-1,

8.5 Sm-1, 13 Sm-1 and 14 Sm-1. The experimental results are compared with numerical simulations (see Fig. 3),produced by three-dimensional simulation software MAXWELL. Beside the fact, that the results are in good

(1)

(2)

(3)

flow

agreement with each other, it can also be seen that there is a linear dependence of the Lorentz force on the flowvelocity in both experiment and numerical simulation. This is consistent with the theory of Thess et al. [1].

Fig.Fig.Fig.Fig. 2222:::: DiagramDiagramDiagramDiagram depictsdepictsdepictsdepicts anananan exampleexampleexampleexample ofofofof thethethethe stepstepstepstep responseresponseresponseresponse behaviorbehaviorbehaviorbehavior ofofofof thethethethe LFFLFFLFFLFF duringduringduringduring aaaa turnturnturnturn on/offon/offon/offon/off scenarioscenarioscenarioscenario ofofofof thethethethe saltsaltsaltsalt waterwaterwaterwater

flow.flow.flow.flow. Here,Here,Here,Here, thethethethe saltsaltsaltsalt waterwaterwaterwater hashashashas anananan electricalelectricalelectricalelectrical conductivityconductivityconductivityconductivity ofofofof 6.56.56.56.5 SmSmSmSm-1-1-1-1 andandandand underliesunderliesunderliesunderlies anananan accelerationaccelerationaccelerationacceleration betweenbetweenbetweenbetween 0000 msmsmsms-1-1-1-1 (pump(pump(pump(pump off)off)off)off)

andandandand 3.03.03.03.0 msmsmsms-1-1-1-1 (pump(pump(pump(pump on).on).on).on). Furthermore,Furthermore,Furthermore,Furthermore, thethethethe filteredfilteredfilteredfiltered redredredred curvecurvecurvecurve indicatesindicatesindicatesindicates anananan increasingincreasingincreasingincreasing basic-plateaubasic-plateaubasic-plateaubasic-plateau (BP(BP(BP(BP ---- nononono fluidfluidfluidfluid flow)flow)flow)flow) orororor

respectivelyrespectivelyrespectivelyrespectively aaaa drift,drift,drift,drift, causingcausingcausingcausing bybybyby thethethethe heatheatheatheat transmissiontransmissiontransmissiontransmission fromfromfromfrom pump.pump.pump.pump.

The encouraging result of this comparison is that it proves the applicability of LFV to weakly conductingelectrolytes. However, it must be emphasized that this preliminary experimental setup is not an optimized fluidflow design and does not provide any information on the flow dynamics inside the duct and their influence onthe total Lorentz force. In order to overcome these disadvantages, a new measurement system has been built.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

20

40

60

80

100

u in m/s

F in

µN

Fig.Fig.Fig.Fig. 3333:::: MeasurementMeasurementMeasurementMeasurement resultsresultsresultsresults ofofofof thethethethe pendulumpendulumpendulumpendulum experiment.experiment.experiment.experiment. TheTheTheThe graphgraphgraphgraph showsshowsshowsshows thethethethe relationshiprelationshiprelationshiprelationship betweenbetweenbetweenbetween thethethethe velocityvelocityvelocityvelocity ofofofof thethethethe saltsaltsaltsalt

waterwaterwaterwater inininin thethethethe testtesttesttest sectionsectionsectionsection andandandand thethethethe measuredmeasuredmeasuredmeasured LorentzLorentzLorentzLorentz forceforceforceforce whichwhichwhichwhich isisisis actingactingactingacting onononon thethethethe magnetmagnetmagnetmagnet system.system.system.system. TheTheTheThe differentdifferentdifferentdifferent linelinelineline typestypestypestypes andandandand

pump off

BP1

BP3

pump on

BP2

symbolssymbolssymbolssymbols representrepresentrepresentrepresent differentdifferentdifferentdifferent electricalelectricalelectricalelectrical conductivitiesconductivitiesconductivitiesconductivities fromfromfromfrom 2.32.32.32.3 SmSmSmSm-1-1-1-1 (rectangle),(rectangle),(rectangle),(rectangle), 6.56.56.56.5 SmSmSmSm-1-1-1-1 (triangle-down),(triangle-down),(triangle-down),(triangle-down), 8.58.58.58.5 SmSmSmSm-1-1-1-1

(triangle-up),(triangle-up),(triangle-up),(triangle-up), 13131313 SmSmSmSm-1-1-1-1 (circle)(circle)(circle)(circle) andandandand 14141414 SmSmSmSm-1-1-1-1 (cross)(cross)(cross)(cross) withwithwithwith thethethethe correspondingcorrespondingcorrespondingcorresponding numericalnumericalnumericalnumerical simulationsimulationsimulationsimulation resultsresultsresultsresults (lines).(lines).(lines).(lines).

(2)(2)(2)(2) EMFEMFEMFEMF SetupSetupSetupSetup

Fig.Fig.Fig.Fig. 4444:::: Left:Left:Left:Left: SketchSketchSketchSketch ofofofof thethethethe EMF-setup.EMF-setup.EMF-setup.EMF-setup. TheTheTheThe mainmainmainmain partspartspartsparts areareareare thethethethe LFFLFFLFFLFF //// EMFEMFEMFEMFbalancebalancebalancebalance (1),(1),(1),(1), thethethethe well-definedwell-definedwell-definedwell-defined fluidfluidfluidfluid channelchannelchannelchannel mademademademade

outoutoutout glassglassglassglass fiberfiberfiberfiber reinforcedreinforcedreinforcedreinforced plasticplasticplasticplastic (2)(2)(2)(2) withwithwithwith thethethethe 1.51.51.51.5 mmmm longlonglonglong testtesttesttest sectionsectionsectionsection (3)(3)(3)(3) andandandand aaaa magneto-inductivemagneto-inductivemagneto-inductivemagneto-inductive flowmeterflowmeterflowmeterflowmeter (4)(4)(4)(4) workingworkingworkingworking asasasas

referencereferencereferencereference measurementmeasurementmeasurementmeasurement device.device.device.device. Right:Right:Right:Right: PicturePicturePicturePicture ofofofof thethethethe experimentalexperimentalexperimentalexperimental setup.setup.setup.setup.

In order to overcome the disadvantages from the pendulum setup an improved setup has been built.Besides the new measurement method which is applied to the new setup (so-called EMF balance; acronym forelectromagnetic force compensated balance), the new fluid channel enables the possibility to adjust the fluidprofile within the measurement test section (turbulent mean profile or laminar profile, obstacles, etc.). Thatmeans the new setup helps to understand the effect of the flow profile on the total Lorentz force. This isimportant because extensive numerical simulations show an influence of the total Lorentz force in the order ofseveral percent.

With the new measurement device - EMF balance - a much better response characteristic is expected.EMF is a direct measurement technique whereas the pendulum setup is an indirect technique.

3333 OngoingOngoingOngoingOngoing workworkworkwork

Two main steps are planned. The first is to investigate the pendulum setup in order to determine the majorerror sources to the total Lorentz force. For example the influence of heat fluctuations to the pendulum setup(see Fig. 2). For this, a heating coil will be applied to the channel in order to adjust certain temperature profilesduring the fluid flow measurement.

The second step includes further measurements with the new EFM prototype under variation of flowvelocity, conductivity and flow profile of the fluid. Furthermore, it is planned to apply a sophisticated magnetsystem - so-called Halbach array. Numerical simulations suggested that the Lorentz force could be tripled withsuch an array system. That means, with this new array system it is possible to increase the distance between thetwo magnets from 32mm to 56mm and still have about the same Lorentz force.

(1)(3)

(2)(4)

4444 ConclusionConclusionConclusionConclusion

The applicability of Lorentz Force Velocimetry for the flow measurement of poorly conductingelectrolytes is demonstrated using experimental results on salt water flow exposed to a permanent magnetsystem. The results provide a linear relationship between the measured Lorentz force, the flow velocity and theconductivity consistent with the theoretical scaling laws. Further measurements are currently being performedon a new experimental setup - an EMF prototype. The new experiments are aimed at investigating the effect offlow dynamics on the measured total Lorentz force.

5555 AcknowledgmentAcknowledgmentAcknowledgmentAcknowledgment

The authors are grateful to the German Science Foundation (Deutsche Forschungsgemeinschaft) forfinancial support of the presented work in the framework of the Research Training Group (Graduiertenkolleg)“Lorentz Force Velocimetry and Lorentz Force Eddy Current Testing” (GRK 1567/1) at Ilmenau University ofTechnology.

ReferencesReferencesReferencesReferences[1] A. Thess, E. Votyakov, B. Knaepen, O. Zikanov: Theory of the Lorentz force flowmeter. New Journal of Physics, 9, 299,

2007.

[2] A. Thess, E. Votyakov, and Y. Kolesnikov: Lorentz force velocimetry. Physical Review Letters, 96 (164501), 2006.

[3] Y. Kolesnikov, C. Karcher, and A. Thess: Lorentz force flowmeter for aluminum - Laboratory experiments and plant tests. Met.

Trans.B., 42B (441-450), 2011.

[4] M. Werner and B. Halbedel: Optimization of NdFeB Magnet Arrays for Improvement of Lorentz Force Velocimetry to be

published in IEEE Journal of Transaction on Magnetics, special Issue for INTERMAG Conference, 2012.

[5] A. Wegfrass, C. Diethold, M. Werner, T. Fröhlich, B. Halbedel, F. Hilbrunner, C. Resagk, A. Thess: A Universal Noncontact

Flowmeter for Liquids, Appl. Phys. Lett., 100 (194103), 2012.

Biography:Biography:Biography:Biography:WEGFRASS, Andre; Dipl.-Ing.; Ilmenau University of Technology

E-mail:E-mail:E-mail:E-mail: andre.wegfrass@tu-ilmenau.de