David M. Feener,Don Lundberg,

VORTAB

General ManagerStaff EngineerCompany

ABSTRACT creates a challenge for the operator to determinethe "real" flow in his plant.

This paper explores solutions to Vortex SheddingFlowmeter error by isolating upstream flowdisturbances with the use of a VORTAB FlowConditioner.

The process controls industry is required tomeasure flow more accurately to meet plantoperation and cost accounting objectives. Recentstudies have shown that the accuracy of manyflowmeter technologies, including VortexShedding Flowmeters, are adversely affected byflow disturbances within forty diametersupstream of the flowmeter. In addition, manyflowmeter installations are not designed with theflowmeter manufacturer's recommended straightrun of piping, because plant sizes are beingreduced to save costs. Upstream flowdisturbances result in poor flowmeter performanceand unacceptable errors in flowmeter accuracy.

VORTAB Flow Conditioners utilize anti-swirl tabsand vortex tabs that are attached to the insidediameter of the flow conditioner body (Figure 1) toremove fluid rotation and irregular flow profilesfrom the flow stream. The result is a flat, nonswirling velocity profile at the flowmetermeasurement location (Figure 2). This creates arepeatable, ideal condition to measure flowaccurately regardless of upstream flowdisturbances. The improvement in flowmeterperformance is accomplished economically, with aminimum of pressure drop, in the very harsh anddirty environment encountered in the typicalindustrial plant.

The opposing objectives of reducing plant size andimproving flowmeter accuracy is resolved by usingVORTAB Flow Conditioners to improve flowmeterperformance in non ideal piping installations.This improvement is demonstrated through theuse of flow visualization, a method thatilluminates the flow profile and swirl of flowdisturbances, and by empirically testing a numberof different manufacturer's Vortex SheddingFlowmeters with VORTAB Flow Conditioners.

The results of these tests unequivocally prove thebenefit of the VORTAB Flow Conditioner withVortex Shedding Flowmeters. It is clear frQm thetest data that VORTAB Flow Conditioners isolateadverse flow disturbance effects and improve theoverall repeatability of the Vortex SheddingFlowmeters in both ideal and non ideal pipingconfigurations. All this is accomplished with lessthan a 25% increase in the pressure drop normallyencountered in a Vortex Shedding Flowmeterinstallation.

These flowmeter performance improvements aredescribed in this paper in two ways. First, thephysical improvement in the flow velocity profilehas been demonstrated through the use of a seriesof experimental techniques known as FlowVisualization. These techniques, described in theexperimental section below, show theimprovement from an agitated, swirling, irregularprofile without the VORTAB Flow Conditioner toa uniform, non swirling, flat profile with theVORTAB Flow Conditioner. Second, the accuracyimprovement in both water and air with the use ofthe VORTAB Flow Conditioner for VortexShedding Flowmeters was quantitativelydetermined by a series of calibration runs withdifferent types of flow disturbances introducedinto the flow stream. The results of these testsare presented in this paper.

INTRODUCTION

EXPERIMENTAL

Flow Visualization

Accurate flow measurement is vital to the safe,efficient operation of the modem process plants.Virtually all flowmeter technologies, includingdifferential pressure, turbine, thermal, vortexshedding, ultrasonic, magnetic, and conolis areadversely affected by flow disturbances created bynon ideal piping configurations upstream of theflowmeter. The typical effect of poor piping is anincrease in flowmeter error, often outside of thespecified performance limits of the flowmetermanufacturer. These errors often go undetected,as it is very difficult to make a comparativemeasurement of the actual flow and theflowmeter's indicated flow in the field. This

Experiments were conducted to demonstrate theimprovement of the flow profile and elimination ofswirl downstream of two types of flowdisturbances through the use of a VORTAB FlowConditioner. The first disturbance was created bya divergence in which a two (2) centimeterdiameter pipe expands to a four (4) centimeterdiameter clear acrylic pipe. The seconddisturbance was created by setting up a "doubleout of plane elbow" piping configuration in which

Figure 1VORTAB Flow Conditioner Functional Description

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Figure 2VORTAB Flow Conditioner Velocity Profile at flowmeter mounting location

produce flow disturbances. The Vortex SheddingFlow Meters were connected to both a water andan air flow stand that utilized turbine flow metersas the calibration standard. The turbine metercalibration standard was mounted in accordancewith the turbine flowmeter manufacturer'srecommendations. Data was collected on theperformance of the Vortex Shedding Flowmeterwith various upstream disturbances. The datawas compiled for all three manufacturer's flowmeters and typical results were graphed to com-pare the performance with and without the use ofa VORTAB Flow Conditioner positioned betweenthe flow disturbance and the flowmeter.

a 4 centimeter diameter pipe joined a piping elbowand then traveled two diameters to another elbowthat is adjusted so that it exits in a different planefrom the first elbow. This double out of planeelbow arrangement is then connected to a fourcentimeter diameter clear acrylic pipe. The flowpattern in the pipe is illuminated and recorded ona videocassette recorder. Various "still" framesfrom the videocassette are included todemonstrate the flow conditions downstream ofthe disturbance. The illumination of the flowprofile is accomplished with three differenttechniques.

The first technique is accomplished by mixingsmall particles with the water flow stream andflowing the water/particle mixture at differentvelocities through the divergence flow distur-bance. The particles are illuminated by using alaser sheet light that passes through the clearacrylic pipe at the location where a flowmeterwould ordinarily be mounted. A videocassetterecorder is used to film the movement of theilluminated particles with and without a VORTABFlow Conditioner.

Additional testing was performed to evaluaterepeatability characteristics and measure thepressure drop through the typical Vortex Shed-ding Flowmeter with and without a VORTABFlow Conditioner. The results of these tests arereported below.

RESULTS AND DISCUSSION

Flow VisualizationThe second technique utilizes a wire that passeshorizontally through the vertical clear acrylic pipethat is connected to the noted double out of planeelbow piping configuration. The wire is chargedwith a very short duration pulse of 150 Volts DCthat resultsm the release ofa small stream ofhydrogen bubbles the length of the wire. Thesebubbles follow the swirl and velocity profile of theflow stream. They are illuminated with a conven-tionallight and filmed with a videocassetterecorder. The differences with and without theVORTAB Flow Conditioner are recorded.

The improvement of the flow stream conditionwith the use of the VORTAB Flow Conditioner isclearly seen on the videocassette recording of theflow visualization techniques that are described inthe experimental section. Copies of the completevideocassette are available upon written requestfrom the VORTAB Company. A written descrip-tion and accompanying "still" videocassette frameof the improvements are submitted below:

Technique 1. Laser sheet illumination ofparticle/water mixtureThe final flow visualization technique utilize a red

and green dye stream that are released fromopposite sides of the clear acrylic pipe downstreamof a double out of plane elbow piping configura-tion. The dyes follow the swirl pattern in the flowstream, clearly demonstrating the improvementthat occurs with the use of the VORTAB FlowConditioner.

The flow stream downstream of the divergencewithout the flow conditioner shows a highlyagitated condition of the illuminated particles(Figure 3). The particles travel from side to sidein the pipe. This is characteristic of a highlyturbulent condition associated with the flowdisturbance and indicates the position in the pipedownstream of the divergence is not a goodlocation for flowmeter placement.Vortex Shedding Flowmeter

Performance With and Without VORTABFlow Conditioning

Three different manufacturers' Vortex SheddingFlow Meters were evaluated with and without aVORTAB Flow Conditioner for the adverse effectsof several different piping configurations that

The flow stream downstream of the divergencewith the VORTAB Flow Conditioner shows amuch more orderly pattern of the illuminatedparticles (Figure 4). In this instance, the side toside movement of the particles is greatlydiminished, and a regular pattern of vortices that

Figure 3Laser sheet illumination of water/particle mixturereveals significant side to side turbulence of particlesdownstream of unconditioned flow disturbance

Figure 5Front view of hydrogen gas bubble illumination revealsirregular flow profile and swirl downstream of a doubleout of plane elbow flow disturbance

Figure 4Laser sheet illumination ofwaterlparticle mixturereveals parallel flow path of particles downstream offlow disturbance with a VORTAB Flow Conditionerisolating the disturbance

Figure 6Side view of hydrogen gas bubble illumination revealsirregular flow profile and swirl downstream of a doubleout of plane elbow flow disturbance

are generated by the vortex tabs of the VORTABFlow Conditioner are apparent. Theimprovement is dramatic, and the orderlyprogression of the particles in the flow reveals asignificant improvement of the disturbance -making it an ideal location for a Vortex SheddingFlowmeter.

In the first view, the flow disturbance is filmedwithout the installation of a VORTAB FlowConditioner. A length of wire is mountedhorizontally across a vertical flow plane (Figure5), and the wire is pulsed with a 150 VDCelectrical charge. This creates a line of hydrogenbubbles that follow the flow profile downstream.As the bubbles leave the wire, the velocity ishighest on the side of the pipe that is opposite theentrance to the elbow. In addition, rotation of theflow stream is apparent, as the bubbles begintwisting downstream of the wire. The swirlingmotion of the flow steam is confirmed in thesecond view where the videocassette camera ismounted for a side view position looking down thelength of the wire (Figure 6). In this case, the flowbegins rotating immediately downstream of the

Technique 2. Hydrogen gas bubbleillumination

Two views were employed to illustrate thedifferences in swirl and flow profile pattern withand without the VORTAB Flow Conditionerdownstream of a double out of plane elbow pipingconfiguration.

Figure 7Front view of hydrogen gas bubble illumination revealsa homogeneous, flat profile downstream of a double outof plane elbow flow disturbance with a VORTAB FlowConditioner isolating the disturbance

Figure 9Colored dye injection into flow stream reveals swirldownstream of a double out of plane elbow flow distur-bance

Figure 10Colored dye injection into flow stream reveals the dyestreams following the flow without swirl thus isolatingthe double out of plane elbow disturbance with aVORTAB Flow Conditioner

Figure 8Side view of hydrogen gas bubble illumination reveals anon-swirling, stable profile downstream of a double outof plane elbow flow disturbance with a VORTAB FlowConditioner isolating the disturbance

wire creating a spread of bubbles across thediameter of the pipe.

Technique 3. Colored dye injection

When the VORTAB Flow Conditioner is locatedbetween the flow disturbance and the cameraposition, the camera records a very different flowprofile. With the wire mounted horizontallyacross a vertical plane, the bubbles leave the wireuniformly and move downstream in unison (figure7). The flat flow profile is very obvious. There isno evidence of rotation of the flow stream in thisview. This is confirmed when the second view(Figure 8) is observed as the bubbles stay in linewith the wire as they move downstream. Thisclearly shows that there is no swirl in the flowstream.

The presence of swirl downstream of a double outof plane elbow piping configuration without theVORTAB Flow Conditioner is clearly seen in thevideo cassette recording (Figure 9). The red andgreen dyes rotate over one another in the flowstream clearly indicating swirl. This effect iscompletely eliminated with the use of theVORTAB Flow Conditioner (Figure 10). Instead,the dyes follow the flow directly downstreamstaying in line with the injection point. It isevident that the flow conditioner stops the swirlthat is introduced by the double out of plane elbow

piping configuration.

specifications. This can create serious issues inprocess plants that depend on the performance oftheir flow meters for safe and efficient operation.This problem is becoming more serious as systemsbecome more automated and plant sizes arereduced to save floor space.

Vortex Shedding FlowmeterPerformance With and Without VORTABFlow Conditioning

VORTAB Flow Conditioners can greatly improvethe performance of Vortex Shedding Flow Metersby eliminating swirl and creating an ideal flat flowprofile at the measurement point. This can bedemonstrated through techniques of flow visual-ization and empirical testing in the calibrationlaboratory. This performance improvement isaccomplished with minimal pressure drop throughthe VORTAB Flow Conditioner.

These documented performance improvementsenable plant operators to have higher confidencein their flowmeter measurements, while permit-ting plant designers to reduce the straight runlengths of their flowmeter installations. The useof VORTAB Flow Conditioners improve overallflowmeter performance in shorter straight runinstallations.

The data that was collected for the threemanufacturers' Vortex Shedding Flow Meters wascompiled and representative results are shown onFigures 11- 20. The graphs show that the VortexShedding Flowmeter has errors of up to 2.5% ofreading as a result of upstream flow disturbances.Various upstream piping configurations wereused to introduce flow disturbances into bothwater and air flow streams. These pipingconfigurations included a single elbow, a doubleout of plane elbow, and a reducing arrangement inwhich a four inch pipe is reduced down to a twoinch pipe upstream from the VORTEX SheddingFlowmeter and the VORTAB Flow Conditioner.With the use ofaVORTAB Flow Conditioner, theVortex Shedding Flowmeter's error is reduced tobelow 0.5% of reading. In addition, therepeatability of the Vortex Shedding Flowmeterincreased by an average of 29% in water (Figure21) and 27% in Air (Figure 22) with a VORTABinstalled. The repeatability graphs examine eachdata point and represent an average of all the testruns detailed in figures 11- 20. The datapresented shows conclusively that it is notnecessary to pair the VORTAB Flow Conditionerwith a VORTEX Shedding Flowmeter duringcalibration in water. In air, pairing of theVORTAB Flow Conditioner and the VORTEXShedding Flowmeter is recommended duringcalibration to provide the best accuracy.

ACKNOWLEDGEMENT

The authors thank Steve Harrington, Ph. D.,Flowmetrics, for his assistance in completing theflow visualization work presented in this paper.In addition, the authors thank Mike Barnwell,Yokogawa Industrial Automation; Jim Pomroy,Rosemount; and Dennis Ciricarelli, Bailey FisherPorter, for providing Vortex Shedding FlowMeters to test. Finally, special thanks are ex-pressed to Dan McQueen, Fluid Components IntI,for providing access to the FCI flow facility tocomplete the calibration work.

Vortex Shedding FDrops With and WiFlow Conditioning

Data was collected on pressure drop measure-ments through the Vortex Shedding Flowmeterand the VORTAB Flow Conditioner and wascompiled with representative results shown inFigure 23. The pressure drop of a VORTAB FlowConditioner adds less than 25% additional pres-sure drop over the pressure drop created by theVortex Shedding Flowmeter without the VORTABFlow Conditioner installed.

REFERENCES

1 Funess, Richard, Ph. D., The Effect of Installa-tion on the Performance of Flow Meters,Flowmeter Training Class, London, UK, 1997Morrow, Thomas, Ph. D., Tutorial- OrificeFlow Metering and Installation Effects, 1996ASME Fluids Engineering Division SummerMeeting, San Diego, CA, July 9, 1996Smith, Chuck, Ph. D. and Hopper, Peter,VORTAB Corporation Technical Brochure,1989

2.

CONCLUSIONS 3

Flow disturbances adversely affect flowmeterperformance by creating swirl and irregular flowprofiles. The resulting errors often exceed theflowmeter manufacturers' published accuracy

1755 La Costa Meadows DriveSan Marcos, CA 92069 USATelephone: 1-760-736-6114

Telefax: 1-760-736-6250Home Page: www.vortab.com/flow

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