fluid flowmetering

8/7/2019 fluid flowmetering

1/236


2/236


3/236

---_ -~-- .. _.__

Handbook ofFLUID FLOWMETERING

1st Edition

by Ing C.J.Benard


4/236

ISBN 85461-120--7

COPYRIGHT 1988THE TRADE ~ TECHNICAL PRESS LIMITED

Allrights T6enedThis b.o.okis sold subjec:, 10 the condi tion tnat it shul! 1I0t hy H.ayof trade or otherwise be

resold. lent. h.1red.aul. slor~d m a rClri(!1"al_~.\.Hr:m.rproduccd or translated into a machine languageo r o 'h e~wl se c rrcu la ted. ln . a~ lYo rm o f bmd il lg o r nno!'r other thun {hal in. which it i s p ublis hed. .

without the PubllSh~,: sprl~r c-C: l Isenr and Idrhow (Isimilar condi tion including Thiscondi tion bemg lmpo.H>(/ O l tiu: _fHf)_\"(qIU1J/ purchaser.

Other books inthis series include:Hydraulic Handbook

Seals and Scaling HandbookHand bo ok o f Ho se , Pi pe s. Cou pli np a nd F it tme sHandbook of Power Cyl inders . Valves and Con tr~o ls

Pneu rnatic HandbookPumping ManualPump User, Handbook

Submers ible Pumps and their ApplicationsCentr ifugal Pumps

Handbook of Valves, P ip ing and P ipel inesFil ters and Fil trat ion HandbookHandbook of Noi se and Vib ra ti on Con tr ol

Handbook of Meehan i ca l Power DrivesIndus tr ial Fas teners HandbookHandbook of Indus tr ial Mater ial,

Published bvThe Trade & Technical Press LimitedCrown House, Morden, Surrey SM4 SEWEnglandPrinted ill Great Bri ta in by TTP (Pr imers) L im it ed , Eas t Mol esey , Surrey. Eng land ,

1II

PREFACETHE MONITORING and measuring of industrial processing has become almostan art form, The dipstick and the simple gauge has given way to high technologicalinnovation of such complexity that the average engineer or technician can easi lyf ind himself, or herself , at logger heads with management or colleagues as to thetrue flowof a given liquid, or gas, in a closed circuit. This ishardly surprising, whenthere are so many methods and measurement systems on the market. Some arecost-effective inthe short term, others require long term investment. Naturally, itdepends on the degree of accuracy required, the elimination of all misleadingfactors and the need for instant data on t rue flow, In some processes, minuteaccuracy is vital and the cost of obtaining same is secondary, In thesecircumstances, only the best will do. The difficulty comes in those circuits where theelimination of all factors detrimental to dead accuracy may not be necessary andcost plays a large part in determining what method and equipment should be used.Second best i s never acceptable, but the best relative to the circumstances i snecessary.For this reason, the HANDBOOK OF FLUID FLOWMETERING has beenproduced as a first source of reference for users of all types of flowmeters andmeasurement systems. It provides a comprehensive understanding of thefundamentals, principles and detailed information on every type of flowmeter, itsapplication and effectiveness . Fur ther , i t covers aspects of which the operatorshould be aware to obtain optimum results and the basis for the correct , and best ,flowmeter or system within given parameters.Much information is provided on calibrat ion methods, l is ting the major testhouses worldwide, Guidelines on how diff icult process f luids , such as adds andcryogenics, affect flowmeter calibration are included aswell as comprehensive dataon density and viscosity, these being closely associated with flow measurement. Asa considerable number of flowmeters are used purely as sensors in a flow controlsystem, an introduction to flow control is incorporated.There is a Buyers' Guide with names and addresses of manufacturers andsuppliers to help the user in obtaining further information, manufacturers ' data,and current prices.The 'Handbook of Fluid Flowmetering ' is a pract ical work of reference full ofvit al and useful information, data, tables and charts, to assist consultants,designers , engineers and plant operators in solving their par ticular problemsassociated with flow and flow measurement.

The Publishers.

ACKNOWLEDGEMENTSAble Instruments andControls British Standards instituteHandbook ofAvia tion Fuel Robert Maurer M,ScProperties

GEe AvionicsLtd(P,S,Division)National EngineeringLaboratory


5/236


6/236

VI

SECTION 7- Multi-phase FlowMeasurement techniquesMixers _ _ _ _ _ _ _ _ _SECTION 8 - General AspectsMetering steam _ _ _ _ _ _ _ _ _ _ _ _ _Metering puimps _ _ _ _ _ _ _ _ _ _ _ _

Pulsating, fluctuating and transient flowAir elimination _ _ _ _ _ _Secondary instrumentationFlowmeters and safety __Flowmeter ins tallat ion __

SECTION 9 - Flowmeter CalibrationGeneral principles _ _ _ _ _ _ _ _ _ _ _Effect of pipework on flowmeter calibrationCalibration of flowmeters for liquids _Cal ibration of flowmete rs for gases _ _ _ _ _Effect of the process f luid on flowmeter cal ibration _SECTION 10- Flow ControlPrinciples and techniques _ _ _Valve selection _ _ _ _ _ _ _ _

SECTION 11- Density and ViscosityDensity measurement _ _ _Viscosity measurement __SECTION 12- Engineering DataSECTION 13Editorial IndexBuyers' Guide _

2 2 92 3 32 3 72 3 92 4 12 4 52 4 92 5 72 6 32 6 72 7 32 8 33 0 33 1 13 1 53 2 53 3 33 6 13 8 94 0 5413

~~-~.- ...-----------


7/236

VIII IX

ACKNOWLEDGMENTS - ILLUSTRATIONS AND TABLES

Page Number Company Page Number Company1 Flow Measurement Control 59 Endress &Hauser2,top Hayden Nilos Conflow L td 60 Kent Industrial Measurement2,boltom Webster Instruments 66 .bottorn Foxboro Co15 Kent Industrial Measurements 67,top All ison Engineering Ltd17 Kent Industrial Measurements 67,bottom Kent Industrial Measurement18 Kent Industrial Measurements 68,top Hydril AOT Aow System19 Kent Industrial Measurements 68 ,bottom Brown Boveri Kent20 Kent Industrial Measurements 69,top Kent Industrial Measurement25 KDG Flowmeters 69,bottom Brown Boven Kent26 Flow Technology Inc 70 Endress &Hauser27,top Stanhope Fluid Power 71,bottom Danfoss Flwometering27,bottom Daniel Instruments 73 Bestobell Sparling28,top Bestobell Meters 74,top Bestobel! Meterflow Ltd28,bottom Daniel Instruments 75 KrohneGmbH30 Kent Industrial Measurements 78,top Bestobell Sparling Ltd31 ,top KDG Aowmeters 79,top Able Instrument &Controls31 ,bottom Maurer I ns tr umen t Co L td Ltd &Controlotron Corp33 Maure r I ns tr umen t Co L td 79, bottom Krohne Measu rement s L td34,top Maure r I ns tr umen t Co L td 81,top Danfoss34,bottom Permex Ltd 82,middle Danfoss35 Maure r I ns tr umen t CoL td 85,bottom Panarnetric Corp36 Maure r I ns tr umen t Co L td 86 Nusonics Inc37 Kent Industrial Measurement 87 Danfoss38,top Hydril AOTSystems 88 International Controls Corp38 ,bottom Diessel GmbH &Co Ltd39 Diessel GmbH & Co 89 Kent Industrial Measurements42,top litre Meter Ltd 91 Endress & Hauser92 Bro"T I Boven Ken t42,bottom Maurer Instrument Co Ltd 93,top Brooks43.top Rhodes &Son 93,bottom Kent Industrial Measurements43,bottom L it re Meter L td 95 Yew44,top Litre Meter Ltd 96 Fischer &Porter44,middle Bestobell Mowbray 97 Fischer & Porter44,bottom Ranger Instrument Co l00,bottom Ameter Inc45,top KDG Flowmeters I01,top Perflow46,top Ranger I ns tr umen t Co 101,botlom KDG Flowmeters46,middle Litre Meter Ltd 102,bottom Fischer & Porter46,bottom Guest &Chrimes 103 KDG47,top Guest &Chrimes 106 KytolaKy47,bottom Bestobell &Mowbray 108,top Ameter48 Rhodes & Son I08,bcttom KDG50,both Ramapo Instrument Co 110 Rotar ne te rs (KDG) Air52 TamoLtd 111 Rotameter s (KDG) Air54,both Moore 119,both Per ry Equ ipment Corp55,table Moore 120,both Daniel Indus tr ies Inc55,bottom Moore I2l,top Furness Controls Ltd51 Endress & Hauser 121,middle Furness Con tr ol s Ud

----------- '--------~-~--


8/236

X

Page Number Company Page Number Company121.bottom Maurer Instruments Ltd 202.all Solartron122 Maure r I ns tr umen ts L td 203.10P Paar Scienti fic Ltd123,middle Dan ie l I ns tr umen ts I nc 205 GEC Avionics123.bouom Daniel Instruments Inc 207 Maure r I ns tr umen ts L td124 Fischer & Porter 208,both Maurer Instruments Ltd125 Fischer & Porter 209,bottom Brooks Inst Div Emerson126.bolh Perry Equipment Corp Electrics127,all Kent Industrial Measurements 2l0.top Danfoss11 8 Kent Industrial Measurements 11O,bollom Lee Eng ineeri ng L td131.bottom Taurus Controls Ltd 211.[op Eurocontrol132,bonom Taurus Controls Ltd 211.boltom Maurer Instruments Ltd135 GEC Avioncis Ltd 114.bottom Brooks lnst DivEmcrson136.both ICC Electrics137,bottom Gilflow 2l6,top Sarasota Automation138 Gilflow 216,bottom Weber Sentec GmbH139.both Spira. Sarco 217,top Weber Scn tec GmbH140,top Spirax Sarco 217,bollom Euromatic14Ltop UCC International Ltd 222,both Kent Industrial Instruments143 Perflow Ins truments Ltd 230 J is koot Autocon tr ol L tdl44.top Perflow Instruments Ltd 23I,top Euromatic Flowrneters Ltd144.bottom Kent Industrial Measurements 231,bottom Auburn International145 Litre Meter 238 Spirax Sarco146.top Litre Meter 239,both Pump Eng ineeri ng L td146,middle G.A-P la ton L td 240 Pump Eng ineeri ng L td146.bottom KDG 246 Atlantik-Geratebau GmbH152 Maurer Instruments 247,top Atlantik-Geratebau GmbH153,top Maurer Instruments 249 Daniel Instruments IncI53.bottom Hydri l Div , AOT Flow Sys tems 250.both Jiskoot Autocontrol Ltdl54.top Maurer Instruments 251 SiemensI 54,bottom Technitron (UK) 252 .riskoot Autocontrol Ltd159.top Fischer & Porter 254 Newport Electronics160,bottom Air fl ow Development s L td 2 55 , to p a nd Newpo rt El ec tr on ic s165 Disa Elektronik A/S centre166 National Engineering 255,bottom Brown Boveri KentLaboratory 257 Measu rement Technology L td168 Dantek Electronic 258 Measu rement Technology L td170.top Weber Sen tec GmbH 260 Safety Technology Ltdl70,bottom Air fl ow Development s L td 268 National Engineering173 Air fl ow Development s L td Laboratory174,top Airflow Deve ioprnents Ltd 270.bottom Brooks Instruments Ltdl74,botlom Scheme Engineering Ltd 271,top Kent Industrial Instruments180 VAFlnstruments 271.bottom Hydril AOTSystems181 Litre Meter 275,top Maurer Instruments Ltd182,top Brooks Ins t Div Emerson 275,botlom A.S.M.E.

Electrics 276 A.S.M.E.182.bo(tom VAF instruments 277 A.S.M.E.l83.top VAF Instruments 278 Daniel Ins truments Inc183,bottom KDG Flowmeters 279 Maure r I ns tr umen ts L td184 Brooks Ins t Div Emerson 281 Daniel Ins truments IncElectrics 282,top Daniel Instruments IncISS,top Arkon Instruments 282,bottom K.J.Zanker186 Brooks Ins t Div Emerson 287, top Sira

Electrics 296 Maure r I ns tr umen ts L td187.a11 Brooks lns t Div Emerson 297,top Maure r I ns tr umen ts L td

Electrics 297.centre Brooks (Instrument Div188,top Liquid Controls of Emerson)I88,bottom Fluidyne Instrumentation 299 Avery Hardoll Ltd189,top J is koot Autocon tr ol L td 301 Ameter189,bottom VAF Instruments 305 NEL190.top Brooks Ins t Div EmeTSOn 307.top NEL

Electrics 307,bottom British Gas Engineering190,bottom VAF Instrume nts Research Station19l.top VAF Instruments 308 NEL192 VAF Instruments 322 J is koot Autocon tr ol L td199 Brooks 323 J is koot Autocon tr ol L td200 Endress &Hauser 324 J is koot Autocon tr ol L td

---- _----_._ -

Page Number325326334,top336335336337,top337,bottom338,table I339 ,t ab le 2342,table3

CompanyFisher ControlsFisher ControlsNixon Ins tr umen ta ti on L tdSolartron

Page Number363 .t ab le 1370

XI

CompanyClandon Scientific LtdPerry's 'Chemical EngineersHandbook' , McGraw Hil lBook Co Inc . N.Y.UCCThe Petroleum EngineerToray Indus tr ies IncUCCUCC

SolartronA utomation Products IncJiskoot Autocon tr ol L tdFischer & PorterFischer & PorterFischer & Porter

3783 8Lt ab le 1 2386,top400401


9/236

XII

SECTION 1Fundamentals and Principles

CLASSIFICATION OF FLOW MEASUREMENT SYSTEMSDEFINITIONSMEASUREMENT ACCURACYPRELIMINARY FLOWMETER SELECTION


10/236

Classification of Flow MeasurementSystemsTHE NEED for an accurate and cost effective method of measuring fluid flowgrows daily, particularly when it is necessary to establish the cost of a certainamount of liquid which has passed through a line. Flow measurement is alsoessential in the process industries as more and more processes are automated. Itisestimated that 'flow' is the third most important parameter to be measured inindustry.A prerequisite of accuracy in flow measurement is that the flowmeter isrepeatable. Many flowmeters operate in difficult environments and often handlecorrosive fluids or erosive slurries. Flowmeters also operate at extremes of

The precision f lowmeter insta lled in adairy.

------ - --- -------------


11/236

2 FUNDAMENTALS AND PRINCIPLES

temperatures handling hot o r cryogenic flu ids. These factors wi ll cause loss ataccuracy tooccur. Often f lowmeters are only repeatable on a short term bas is . Forthese reasons, flowmeters need to be re -ca libr ated at regu lar interva ls. Al l newflowmeters should have a calibration certificate issued byan accredited test facility.Normally a flowmeter forms part of a flowrnetering package. The data suppliedby the mete rs can be used in a control system, for trend recording or can be fed toa computer for total flow calculation etc. Most flowmeter manufacturers can supplythe requi red associated equipmen t, such as total isers, batchers, reco rders,

computers, Iinearisers.An increasing application of flow measurement is in hydraulic power systems.Taking the electric hydraulic analogy, in an hydraulic sys tem, the oil hydraulicpump represents the rruotor and the oil f low is the equivalent of the current . Rateof flowmeters are frequently used as the 'ammete rs' in the c ircuit, to monitorsystem performance.

Flowrate meier providing essential flowcharacteristics of hydraulic systems.

Low cost hydraul ic f low indicator wil l monitor up180 lit/min.

CLASSIFICATION OF FLOW MEASUREMENT SYSTEMS 3

Positive displacement f lowmeters, especially those of the gear type are used inhydraulic systems incorporating rams. The ram positions are computed from pulsesgenerated inthe f lowmeter , while the system computes the expected volume in therese rvoir from the ram posit ions and other paramete rs and compares it wi th theactual.The measurement of fluid flowThe process indus tr ies handle a wide range of f luids varying from clean f il teredliquids to pulp and solid materials, which are suspended in a liquid or pneumaticallyconveyed.There are a large variety of flowmeters available. The following can beconsidered as a broad guide to selection.There are basically five types of flowmeters:(i) Rate offlowmeters which measure the average flow velocity over thewhole area of a pipe bore.(ii) Current flowmeters or anemometers, which measure the speed off low of a liquid at one par ticular point in the f lowstream.(iii) Positive displacementflowmeters, which measure the volume passedper unit time. (Volume flow is also measured with speed offIowmeters in which case the speed ismultiplied by the throughflowarea).(iv) Mass flowmeters, which measure the weight of the l iquid which hasflowed through the meter.(v) Cross correlation flowmeters, in which the time is measured for animpurity or a flow disturbance to pass two pick-ups.

Rate of flowmetersThere are three main types of speed off low- or ratemeters :(i) Flowmeters using a propeller or turbine mounted in the flow, therotat ion speed is the measure of the fIowrate. The main f lowmetersin this category are: Turbine, Propeller and Pelton Wheelflowmeters.(ii) Flowmeters in which the flowrate indication is derived from themeasurement ofa pressure drop across a reduction in the f low areaie: Pressure Drop flowmeters. These flowmeters can be subdivided

into Constant Head and Variable Head flowmeters.Constant head flowmeters : Variable gap meters (or rotameters ).Var iable head flowmeters : Orif ice plate; Flow nozzles; Ventur itube; Dall tube; Spring restrained dragbody flowmeters; and Targetflowmeters.(iii) Flowmeters using more recent measuring concepts such as:Ultrasonic; Electro-magnetic; Vortex shedding; Fluidic; and Swirlflowmeters.

Current Oowmeters or anemometersThese are normally manufactured in the form of probes which are inser ted in theflowst ream and can be traversed across the bore of a tube to measure the speed offlowat various positions. The main types are:( i) Inser tion f lowmeters incorporating a turbine, vor tex orother type off lowmeter at the end ofa probe;


12/236


( ii ) Laser doppler anemometers ;( ii i) P itot tubes ;( iv) Hot wire or hot f ilm anemometers .

Positive displacement flowmetersIn these flowmeters the measuring element normally makes contact with the wall ofthe flowmete r body, so tha t li ttl e or no fluid can bypass the measuring elementwithout giving it a positive displacement.The main types of flowmeters in this category are:(i ) Rota ting sliding vane;( ii ) Reciprocating pis ton;( ii i) Rotary piston;(iv) Rotating disc;(v) Flowmete rs with screw rotors or gears.

Mass flowmetersIn these flowrneters the weight ofthe fluid which has passed through the flowmeterisdetermined either by calculation using the fluid parameters or bydirect true massmeasurement. The main types include:( i) F lowmeters using compensation techniques;( ii ) Axial f low transverse momentum;(iii) Linear acceleration;(iv) Hydraulic wheatstone bridge;(v) Rotameters with densi ty compensated f loats;(vi) Thermal mass f lowmeters (mainly for gases) ;(vii) Pressure drop flowmeters calibrated in mass units:(viii) Corona discharge flowmeters (for gases).

Cross correlation flowmetersIn cross correlation measurement an impurity or a dis turbance is introduced intothe f low and the time ismeasured for this to pass two pick-up probes.All the tlowmeters mentioned are described in greater detail invarious chaptersthroughout the book. Information is also given about certain points that thepotential user should know, ie how the flowmeteris affected by the nature of the

f luid measured, pressure and temperature extremes, ins tallat ion conditions andeffects of variations of fluid and flow parameters.

-"-----------~-------------

5

DefinitionsFluid ViscosityTHE COEFFICIENT of viscosity, usual ly termed as viscosi ty, is a figure thatindicates the amount of resistance a particular fluid offers to a shearing force underlaminar flow conditions ie: when one layer of liquid flows relat ive to the other.Viscosity provides a comparative measure between thick heavy oils and petrol, forexample. It is defined more fully and more scientifically in Section 11.Viscosity ofa liquid varies with temperature and, to a much smaller degree, withpressure . In a non-Newtonian liquid, the rat io of shear stress to shear rate is notconstant, but changes with stress. Typical non-Newtonian liquids are: chocolatepaste, ointments, toothpaste, thixotropic paints, bitumens etc.

Reynolds number (Re)This isthe ratio between the momentum ofa flowing fluid and its viscosity. Its valuewil l determine whether the f low is laminar ie: all par ticles f low along s traight ornon-turbulent paths.

Re = _ _ . E Y _ Qn

wherep is the densi ty of the f luidV isthe linear velocityD is the diameter of the pipen isthe dynamic viscosity

With laminar flow fluid viscosity damps out any disturbances; with turbulent flowinertia forces exceed viscous forces and random swirl and eddies will occur.Flow willremain laminar upto a value ofRe = 2000; there isa transition regionbetween Re = 2000 and Re = 5000 when flow willbecome turbulent due to theslightest disturbance. Flow will always be turbulent when Re reaches a value ofapproximately 5000. The larger the f luid momentum and the lower the viscosi ty ,the SOonerturbulent flow will commence.


13/236


Pipe Reynolds number (Rd)In calculations on Orifice Plate flowrneters use ismade ofthe value Rd rather thanRe:

4MIlDn

where:M is the mass flowrateD is the diameter of the pipe11is the kinematic viscosity

Velocity profileFluid wil l always f low fas ter along the centre of a pipe than along the pipewall , asthe frict ion of the pipewall will s low the f luid down in that region. Figures 1 and 2show how the speed of flow varies across a pipe's diameter. This is known as avelocity profile or flow profile.Figure 1 shows the flow profile for laminar flow ie: flow in which viscous forcespredominate.

:-::.;: . . . . . . . . . . . . . . . .".-- -

/~ 77J"

Figure 1Flow pro fi le for laminar f low.Figure 2 shows the flowprofile for turbulent flow. Flow irregularities in the formofvortices and cross currents are superimposed onthe main linear flow, so that flowiss lowed down in the centre of the pipe and accelerated nearer the pipewall . Thiscauses the flow profile to become more flat.Both profiles shown are symmetrical.-

---._ _-'7 7 7f

Figure 2Flow profile for turbulent flow.

..--.---- ... '- ...- .

6(A)

\\\ .,\\\

~\ .~~- \\\ \ \ \\\ \

\~

~."I{DG can monitor ,!;At:1~ -, .~ ' " 'l - ' '" ' " '"KDG Instruments ltdTylors & Rotameter Works59-61 Victoria Road, Burgess HillWest Sussex RH15 9LJ, EnglandTelephone: (04446) 2631 Telex : 87551

L_ ~ ~ ~ __ .__ ....._..


14/236

Control and., .measurement ofliquidsSm it h r ot ar y p os it iv e d is pl ac em en t a nd tu rb in e m et er s f or h ig ha ccuracy cu sto dy t ra n sf er .

POSITIVED lS Pl .A Cl :M E NT M E TE O RWith e l ect r oni C con tr o l of muRi-function oontro v a v e .

POSITIVEDISPLACEMENT METERF or h ig h a cc ur ac y l on g I He .Double or single caseconstruction. Flow ranges from2 cu. mtr . lhr. to 2 , 000 cu . m t r .l h r.Sm it h c o nt ro l v a lv e s, M e ch a ni ca lor Electronic instrumen ts,d e ae r a to r s, f iHe r s, s t ra i ne r s.

T HE FMA GROUP OF COMPANIESP RE MIER H OU SE V IC TO RIA W AY W OKIN G SU RR EY G U21 lO GT elep hon e: (04 862 ) 69 011 T ele x: 85 94 40 F MA G

TlJRBINE METERIn s i ze r an ge f ro m 1 " u p t o 2 4"High a ccur a cy ( O .1 0%possible). Flow range 3-12,000cu. mtrsJhr. Bi-< l irectional flowa v ai la b le . S ta in le s s s te e l o rc a r bo n s t ee l c o n st r uc t io n .P re s su re s u p t o 9 OO1b an s i.F UL L R AN G E E LE CT R ON ICI NS TR U ME NT S A NDACCESSORIES

DEFINITIONS 7

Fully developed f lowIn pract ice flow is seldom neat ly symmetri cal , the flow profile s are normallydistorted byvalves, pipe bends etc. For flowcalibration it isa requirement that flowthrough the flowmeter is fully developed; this means that the flow irregularitieshave had the opportunity to damp out and the flow profile has become fullysymmetr ical and free from swir l. In theory this occurs after the f luid has f lowedthrough an inf initely long pipe. In pract ice this occurs after the f luid has f lowedthrough a pipe the length of which is twenty times i ts diameter, ie the pipe is 20 Dlong. Any changes to the profi le after this length can be neglected.Itisnecessary to have the flow fully developed in a calibration facility to ensurerepeatability of results. .

CavitationIn a flow the va lue pV isconstant, so that when the speed isincreased, the pressurewill drop. If the pressure drop issufficiently large, a phenomenon will occur whichisknown ascavitation. As the pressure drops below the vapour pressure, bubblesof vapour wil lappear and collapse assoon as they enter an area ofhigher pressure.If cavitat ion occurs immediately in front of or ins ide a f lowmeter, the f lowmeterperformance will be affected.Coeff ic ient of dis charge (Cd)This isdef ined for ratemeters as:

VtVi

and for current meters (anemometers ) as:Cd =

Cd = . . . . Q ! _O iwhereOt and Vt are the true f lowrates and flowspeeds as indicatedby a very accurate master flowmeterOi and Vi are the values indicated by the meter i tself. See Figure 3.

0,98

097

096Reynolds number Re

Figure 3Example of characteristic curve based on coefficient of discharge.


15/236

DEFINITIONS8 FUNDAMENTALS AND PRINCIPLESThe Flow Measurement CentreMeter factor FThe meter factor is a s imilar constant as Cd but applied to meters which measuretotal volume: NEED to HIRE or BUYtViF

! .IIIII- !I

K-FactorThe K-factor isused to describe the performance of meters the output of which isin the form of electrical pulses: ACCURATE METERING EOUIPMENTFOR WATER, CHEMICALS, AIR AND STEAMK Vtwheren is the number of pulses per unit timeVt is the volume passed in that t imeThe K-factor isnormally plotted against flowrate.

LinearityA flowmeter is said to be linea r if the f lowmeter read-out isa straight l ine goingthrough the origin when it is plot ted against flowrate. The linearity graph is notnormally plot ted; it is normal to plot the deviation from l inea ri ty because thedeviation from lineari ty is then shown on a larger scale.Velocity headThe pressure drop across a f lowmeter isoften expressed in velocity heads:Velocity head =Y2P y2wherep is the densi ty of the f luidy is the l inear velocity of the f luid

Range and rangeabilityThe range of a flowmeter is normally the. range where it meets the accuracyspecification of the f lowmeter. The rat io of the maximum flowrate of the range tothe minimum flowrate of the range iscal led rangeability or turndown ratio.

CONTACT THE INDEPENDENT SPECIALISTS:FLOWOUIP LTD., BULL CLOSE LANE, HALIFAX HX1 2EF

FAX 0422 330278 [liJ 517658 FLOWOP G'S" 0422 43334

DIGITAL FLOW INDICATORSRATE-TOTAL~~ Pulse inputs

4-20mA inputs

GUADRINAturbne floVln1eters

IN-LINE flowrr"leters,.._ee B in""h ,Ii""""dw u.- gaaeYOIl n"e rlc- or- rn 'Igw wide"P ....... t:i"9 .........e. 100_ no_ apeclllllt:y

P6000Square root extraction.Scaling (MultiplylDivide)Loop powered versionsLoopltransducers excitationProcess loop. BCD andRS232 output options

rNSERT[ON flDWrneters6162_/" ;~

('~""". . . . ,)


16/236

DEFINITIONS

SECTION 1sound levels, propagatlo". of sound,measu rement o f s ound , noise scales andnoise indices . subjective noise par3!"e~eT$lroom acoustics . acoustic rooms. prmc'plesof vibration,SECTION 2aannoyanc e and communi ty r es pons e,health and safety (hear ing damage) , ,speechcommunication, hearing conservation 5nindustry, hearing protective deviCf!$.SECTION2bv ib ra ti on - e ff ec t on peopl e.SECTlON3ano ise me asu rin g te ch niq ue s, so un d l ev elmeters frequency anal'($is (spectrumana l' ($ i5 ), r ecording and . s igna l p r~and data l oggers , env Ir onment al noISemonitoring, audiometry.SECTION3b . .vibration measurement. vIbrationtra . ..dueers, dynamic analysis of vibrat!0n,modal anal'($is, vibration testmg,machinery health monitoring.SECTION4a .machines, bea ri ngs, i nt er na l ?Ombust lo ."engines . construction site eq~lpment, aIrd is vibu ti on S '( $t ems, f an nor se , f ac to rynoise road traffie n oi se , a irc ra ft a ndairport noise, noise in commerci~1 b,:,ildin!l""'noise in domestic buildings, auditoria, nOIsein ships.SECTION Sa sound insu~atio" and absorption, acousticmaterials, aeousne enclosures, soundb arr ie rs a cou st ic tr ea tm en t o f f lo ors a ndcei li ngs: acous ti c g lazing , acous t! c doo!"fan and air duct SIlencers, Industrialsilencers, silencing gasturbines.SECTION 5b .machine balance, vibration isolation,. antI'vi bra ti on moun ts, d ampi ng t ec hmque s,resilient mounting of structures,SECTION 6legislation.SECTION 7buyers' guide, editorial index.~:~~t6~~.N~~~LD~~~iu~~:~~~~EW, ENGLAND.TElEPH-ONE: D1 S4D3897 TElEX:928926 ACROSSG.

.._-------------------. _ ..

9

Measurement AccuracyTHE MOST important parameter of a flowmeter used for custody transfer is itsaccuracy, There can be no accuracy without good repeatability. Repeatability is theflowmeter's ability to give exactly the same output when measuring exactly thesame flowrate. The output of some flowmeters drift with time, after a period ofoperation it will st ill give good repeatabili ty but about a different point.Repeatability can be of greater importance than absolute accuracy eg: in flowcontrol.It is not possible to manufacture a flowmeter where its accuracy can be exactlypredicted, Therefore, it is necessary for each flowmeter to be calibrated. Spotchecking only is not acceptable.If repeatability is required rather than accuracy, it is only necessary to select aquality flowmeter whichhas been type-tested for repeatability.Calibration means to check a flowmeter's output bypassing a range of accuratelyknown flowrates, generated in a flowrig or calibration facility, through the

flowmeter. Ifthe flowmeter output shows errors whichare equal to or lessthan theaccuracy claimed for the flowmeter, it issaid to be within calibration.If a manufacturer claims a certain accuracy for a flowmeter, he should define

what he means by accuracy, how it has been established, what standards have beenused to establish this accuracy and how the standards used relate to nationalstandards of flowmeasurement (traceability).In systems where other parameters have to be measured to arrive at an overalloutput, suchas pressure and temperature, errors inthese parameters willaffect thefinal calculation. The effect of these variations on the overall accuracy has to beassessed.For adequate flowmeter calibration, the accuracy of the test rig used by themanufacturer should be considerably better than the accuracy which will be

claimed for the flowmeter. The user should not just ask fora calibration certificatefor a flowmeter, but also the accuracy of the calibration facility and its traceabilityto national standards.In many cases itwillbe found that the accuracy claimed by a manufacturer for a

flowmeter is the same as the accuracy claimed for his calibration facility. This isnot


17/236


acceptable. Therefore, if accuracy is important to the user, the following should beclearly established:(i) The manufacturer's definition of accuracy.(ii) The accuracy of the manufacturer's flowcalibration facility.(iii) The traceability of his flowrig.

Definition of accuracyWhen a measurement of flowrate is made, the obtained value will deviate by acertain amount from the true actual flow; ihis will be a measurement error. Thiserror will be a build-up of at least two types of error ie: a systematic error and arandom error. The systematic error is the error that cannot be reduced byincreasing the number of readings and taking the average.Random errors are due to a large number ofsmall independent influences andrepresent the non-repeatability of the flowmeter.When the output of a flowmeter is checked, in a calibration facility, at a number

of consecutive flowrates over the flowrange of the flowmeter, a calibration curve(error curve) can be drawn as shown in Figure 1. In the perfect flowmeter, theoutput would be the straight line OA as shown in Figure 2. The errors plotted inFigure 1 are the deviations of the curved linefrom the straight line at each flowrate.All flowmeters have a characteristic curve. This curve has approximately the sameshape asallother flowmeters of the same design and isreferred to asthe signaturecurve of a particular type of flowmeter. The signature curve represents thesystematic errors of the flowmeter. The more accurate the calibration facility themore accurately the error curve can be drawn. The systematic error is increased orreduced by the random errors.

A

.. .g.. ,"e~

g"A

Calibration curveFigure 1Typ ical e rror curve o f a f lowmeter, p lo tt ing dev ia tions from the nominaloutput against flowrate.

----___--._--- ... _.- - - ..._----_. _ _.-._------

MEASUREMENT ACCURACY 11

Figure 2Graph showing how the f lowmeteroutpu t can dev ia te from the ideallinear output.

The curve in Figure 3, shows the variations of the K-factor, ie: the number ofpulses per unit volume, of aturbine flowmeter, and represents the systematic errorsof a turbine flowmeter over its flowrange. The error curve can bederived from theK-factor curve.

Laminarregion

Fully turbulent region

1-factorFlowrate

Figure 3K-factor plotted against flowrate for a turbine flowmeter.


18/236


Figure 4 shows the result s of measurements taken over a ce rtain t imespan at aflowrate which is held constant. The mean value of the random error is thesystematic error. The random errors will have a statistical distribution as shown bythe curve on the r ight of the diagram. The data points deviate from the mean valuein accordance with the laws of chance. The value on the X-axis represents thenumber of readings which were equal to the mean random error or systemat icerror. Itisposs ible to calculate s tatist ical ly the uncer tainty in a measurement dueto random errors (see BS 5844 : 1980Measurement ofFluid) .

Trueflowrate

Spurious errorf Random error= _ _ _ ~ l ~ t ~ _ x _X -->~rr~- X X X 2S l eSystematic error - ---

Time over which Timea constant

Meanmeasurevalue

%nfidencevel

f lowrate isbeing measuredFigure 4Diagram showing 'spread' about the nominal of f lowmeter readings whi le theflowrate isheld constant.

Flow: estimation of uncertainty ofa flowrate measurementThe distribution curve of the random errors are shown separately inFigure 5. Itcanbe shown tha t 95% of the e rrors measured will li ew ithin a band 2S wide, S i s astatistical value known as the standard deviation and iscalculated as follows:

S

whereYiis the ari thmetic mean of the n measurements of the var iable Yi(Yi)r is the value obtained bythe r 'th measurement of the var iable Yiin is the total number of measurements of the var iable YiIn practice it isnot possible to obtain a true est imate of the s tandard deviation,asfor this, in theory, an inf inite number ofmeasurements would have to be taken.The larger the number ofreadings, the more accurate S can be calculated.

MEASUREMENT ACCURACY 13

Systematic1------- error ------lFigure 5Gauss ian dis tr ibut ion curve of a set of random errors.

Ifthe spread ofthe random error or the non-repeatabili ty isclaimed tobe 1%and if this 1% isequivalent to 2Sthen itcan be said that the repeatabili ty of theflowmeter is 1% with a confidence level of95%. (These figures are approximate,for more accurate figures see BS 5844). This error, due to non-repeatability, shouldbe added to the systematic error obtained from the calibration curve.Therefore , to be able to assess the accuracy of a flowmeter, it is necessary toknow the calibration curve of the f lowmeter as well as the non-repeatabili ty of theflowmeter.Strict ly speaking, the non-repeatabili ty of the calibration method should beadded to the non-repea tabi lity of the flowmete r (see a lso BS 5497 : Part I Guidefor the Determinat ion of Repeatabili ty and Reproduc ibil ity for Standard TestMethods).Ifa calibration curve isnot supplied with the f lowmeter, i t iscommon practicejust to give an accuracy figure. This figure then covers both the systematic error andthe random errors. If,for example, an accuracy of 1% isc laimed this can be 1%

of maximum flow, as indica ted by the two dot ted lines parall el to the X-axis inFigure 1. It is r efe rred to as 1% FSD. (Full Scale Deflection).If the manufacturer s tates that the accuracy is 1% off low, the accuracy f iguresfal l between the two l ines OA. Sometimes different pe rcentages are given fordifferent sections of the f lowrange as indicated by the heavy lines in Figure 1.Microprocessors can be used to improve the accuracy of flow measurement anda lso to inc rease the range of some flowmete rs. Flowmeters which are used foraccurate applications are provided with a calibration curve which plots systemerrors ie: those errors which cannot be reduced by taking a large number ofreadings and taking an average. These errors also include the larger errors due tonon-linearities of some flowmeters at the bottom and top flow ranges.Figure 1shows an error curve of a f lowmeter. This error curve can be s tored ina microprocessor, so that for any flowrate the ac tual flowrate for a parti cula rf lowrate (as represented by the s ignature curve) can be determined. For a turbine

>>~>>> ~> - ~


19/236


flowmeter the K-factor curve would be stored in the microprocessor. The errorcurve can 'be s tored as tabulated data, with interpolation in bet:-veen th~ storedpoints, or i t can be expressed as a second or t~ird orde:- polynomial. equatlO~; thecoefficients would have been determined previously using curve fittmg techniquessuch as least squares or cubic spline routines.The vo lume and thus the densi ty of al l liquids i s a ffected by tempera ture . Thedensity of some of the lighter hydrocarbons is also affected by pressure; therefore,ifvolume ismeasured for custody transfer, the volume should always be correcte.dfor base reference conditions, which is 156 C (60.;) although 15C (59 OF) ISnow becoming popular, and 101325 kPa (14696Ibfm a).API Standard 2101 gives combined correction factors for pressure and

temperature.After the accuracy of a flowmeter has been establ ished, the accuracy of thewhole measurement system will have to be assessed.Traceability .Each standard used in a calibration facility should periodically be checke~ a~amsta master standard. The manufacturer's master standard should also be periodicallychecked against a local or national station, so that it ispossible to trace the accuracyof a standard used against a national standard.

15

Preliminary Flowmeter SelectionIN MANUFACTURERS' catalogues, flowrate ranges given are normally those forl iquids and they usually apply for water . F low ranges for gases tend to be a matterfor consultat ion with the f lowmeter supplier in each individual application. Theflow ranges for gases are subject to a number of factors such as pressure,temperature and viscosi ty changes , which do not affect the f lowrates for l iquids tothe same extent. The measurement ofgas and steam flows ismostly carried out withthe aid ofpressure drop devices which, together with vortex meters, are flowmeterswhere the meter coefficient can be calculated theoretically.

3%c-,


20/236

16 FUNDAMENT ALS AND PRINCIPLES

Figure 1shows how the accuracies of sixtypes of f lowmeters compare. Table 1gives a preliminary selection table. The graphs in Figure 2 give approximate costcomparisons of the main types of flowmeters in use. Table 2. shows the metercharacteristics of a number of flowrneters.

TABLE 1 - PRELIMINARY SELECTION TABLE

Type of Flowmeter

Orifice platef ~ Variable ori f ice"Z ~ with spring restrain:c E. Venturi tube2 ~, , - => Pitot tube

Oto 20:11900-000150to15000-8to40-00010 to490-()()()

1-01-01-010

0-250-25

0-1

60006000

3000600

-195 to+400

+550

c.., With glass tube: c ~.!!~~ ~ With metal tube"0. ; . - =

00001 to 6:1 to4000 10:10-001 to15000

2040

0-2505

350 -30 to+100

9300 -200 to+350

-40 to+400-20010+500+290

100

Positive displace-ment flowmeters 0-1 to12-000 120:1 01 to300_01 to0-25 1440 -4010+250 1100

Turbine andpropellerflowrneters01 to2-700000

Pelton wheelmeters 0 .15 to227-000

20:1 to50:1 025 005 10000 -240 to+1380 500

500

~ ~ Magnetic~ '"~~tE 1liUltrasonic'"06 - =

Vortex sheddingflowrneters

0-2101-900000upto7500010to

7-000-000

1.0 0_25 4350 -265 to+400

1000

Target flowmeters up to76rn1s

10:1300:1

20:1

1-01-0FS

05

05

0-15

36253000

1500

-40 to+177

- 2 0 0 to+ 2 0 0-26810+370

1000

True massflowmeters Oto2 2 7 0 0kg/min

10;1 0-5 0-2 5000

025 2000 -40 to+85

PRELIMINARY FLOWMETER SELECTION 17

Metal body VA

PD meter (local read-out}

o 2" 4" 6"Meter diameter

8"

Figure 2Cost comparisons

~


21/236


: , . ! ' !o. . . .+ 1

"#V>. . . . . .6+ 1

>

.,.~~>

":'. . . . . .o- .,, , : , -g0,>... .e_.~u00~~

2 :.,N

.5:: e.5N

.5

E !:o0;::' + - N6+ 1

>.u>.os_....c:: s osu .,u c< : . : :

PRELIMINARY FLOWMETER SELECflON

. ,c:oZe-,g.,;:scr.. , '"....u- . -...co 0. . , . ..ctio < 1 . lZO;

. ,c:oZ

"0.;soon'"U

. . . .o'"'"

"0':Jg.. .o'"'"o

"0':Js. . . .oc 3"0.;s. .'"~o

yoN

.. ,N'0;;..c:.~on.sa>'"0~..c's'"~'">

19

.---~--- ..-----.---


22/236

20 FUNDAMENTALS AND PRINCIPLES2 )~'J ". ~" ~ ,_ ;:;;;-E v-. -:;Z I >" < " ' . ~" .r.t:: -:; V- . ~. g C +1

2v; -::;"J '" ~:~ ~ '::;." " :;. . E ;::~ es ~. : : : ! - '"'" c G " i '"- .r, e. E

~." "::;e :0Z. ~ .g '5 -. : . ; ; ;::: : ; ; ; .. ... . " ;,!i: "i 0 0 c ":;, or, Z Z ECI~: : . :S " - 'r -o" ;::. .= : . .. - .c.r: ~ , .:... ..::; c-. s - '"::..~ ~. ~ ;:: .g" ~ "" ; : : : . "2 " " ~ .~~ :;; C-.~ C " ~- .: : E~ G " ic:' " ~ or, az

:2 '". = " "_) t: i:;:; '" -g" >.- ot '- "" :; .~ . . : : : ;i- E : ; ; : ~I ~ Ne. . . . .E , '" S ;:;'-' i: 3~ 0 " Z "-, N - -o


23/236

20(B)

PUMP USERS' HANDBOOKF. Pollak, MBE, CEng, MIMechE, MIMarEWritten for the benefit of the user, theauthor has concentrated on producing apractical handbook with numerousdiagrams, charts, ready reference tables andmuch technical data throughout. The bookdea ls sys tematica lly with the princ ip les ofpumping, suction performance, the stuffin!J"box, how to enqu ir e fo r, se lec t and orderpumps , e lectric pump drives, sys tems andvalves, p ressure surges and the ir con trol ,hea lth and safety, f au ltf inding and main-tenance, and useful hints for users, 250pages , hard case bound , gold b locked witha dust jacket.

contents:t t te Principles of pumping;Main c lassifica tions of PumpsPhysical propert ies of Uqu~dsRQ\ oo yn am : c p um p .Pcslt ive displacement pumpsSelf-primi.ng rctodvnarnie pumpsHow to make FiQutd f low int o t he pumpWhy , whe th er , a nd now to p rime pumps .How to def ine the tara! pump head lpressure]The stuffing-boxThe choice- of mater ials for pumpsHow to s el ec t a nd o rd er t he c or re ct pumpElec tr ic pomp drivesP tp et ln e sys t" rn s a nd vawes - t he I nl et a nddeli- v e ry s y st emPressur-e surges. ~npipe lines - and controlHow to t es t pumpsHin ts for usersHealth and -sa fe tyAppendices; Insta l la tion, S ta rt ing andoperat ion; Fault F inding and Mainrenil lr ;1ce ;Sec tiona l drawings of pumpt; Mater ia ls fOTP ump s; T echntcaS Data; Bibliography; Index.THE "tRADE ;& TECHNICAL PRESS l iMITED,CROWN HOUSE, MORDEN,SURREY. SM4 5EW, ENGLAND.TELEPHONE : 0 1 5 40 3 89 1T El :E X: 9 28 92 6 ACROS S G .

~ ~_ c c _

PRELIMNINARY FLOWMETER SELECfION 21

Cryogenic liquids can be metered with:Turbine flowmeters,Vortex flowmeters,Positive displacement flowmeters.

Aggressive fluids can be metered with most types of flowmeter; for this. metersmade from special materials are available.As a second s tep the diameter of the pipe, inwhich the meter is to be mounted,can be used as a criterion for selection.For large diameter pipes , approaching 3 m (to ft), the choice of meter wi ll belimited to:Electro-magnetic f lowmeters , i f the l iquid is conductive or ultrasonic f low-meters.

This leaves the cheaper alternative of using an insertion flowmeter to traverse thebore.H the l ine size is very small, down to 1 mm (004 in) or even less, an integralorifice flowmeter is the only choice.Venturi tubes have been made up to 3 m (to ft) in diameter, while Orifice platef lowmeters seldom exceed 1 m (365 in) in diameter. Nozzles are seldom largerthan40 em(15in). Most other flowmeters are available insizesupto 30 em (12 in).As a third step the speed of flow, that a flowmeter can cope with, should beconsidered. To check if a par ticular type of f lowmeter issui table for a par ticularflowspeed, Table 2 shows the maximum flowspeeds for a range of flowmeters.Table 1 shows the temperature and pressure extremes that the flowmeter canstand. The table will also giveaccuracies and repeatabilities, which can be achievedwith var ious flowmeters , so that the range of suitable f lowmeters can be furthernarrowed down.Table 2 shows the pressure drop which can be expected across the f lowmeter invelocity heads.Table 3 shows some typical installation requirements.Further information regarding the suitability of each type of flowmeter will befound in the relevant chapters.


24/236

,lI1!

SECTION 2Rate of Flow Meters

TURBINE FLOWMETERSPELTON WHEEL AND OTHER PROPELLER FLOWMETERSTARGET OR DRAGPLATE FLOWMETERSFLUIDIC FLOWMETERSELECTRO-MAGNETIC FLOWMETERSULTRASONIC FLOWMETERSVORTEX SHEDDING FLOWMETERSSWIRL FLOWMETERSPRESSURE DROP FLOWMETERS - CONSTANT HEADPRESSURE DROP FLOWMETERS - VARIABLE HEADPRESSURE DROP FLOWMETERS - VARIABLE ORIFICESHUNT FLOWMETERS

------------ - - - - --------------- ----------------- ----------


25/236

25

Turbine FlowmetersTURBINE FLOWMETERS consist of a flowtube with a small propeller or turbinemounted co-axial ly ins ide. A typical example isshown in Figure L The turbine ismounted on bearings which intum are mounted inhub assemblies; the support forthe hub assemblies act asflow straighteners at the same time, though these on theirown are not general ly adequate to s traighten the f low.

Figure 1Turbine flowmeter

The bearings can be either plain bearings, ball bearings or hydro-dynamicbearings lubricated by the fluid being metered. The angular velocity of the turbinei s proportional to both the axial ve locity of the fluid and the helix angle of theturbine blades. The angular speed ofthe turbine therefore, isa measure of the rateof f low, usually measured by means of a magnetic pick-up, mounted outside themeter body. A magnetic circuit iscompleted when the tips of the turbine bladespass the pick-up. Pick-ups are ofthe inductance type ifmagnets are mounted on therotor. and ofthe reluctance type if the magnets are mounted inthe pick-up; rotationof the turbine varies the reluctance. The frequency of the output signal isproportional to the rotary speed ofthe turbine which in tum isproport ional to thespeed of f low of the l iquid. The output of the f lowmeter iselectrical and basicallyan a.c, voltage at a frequency proportional to the turbine speed.

------------- .------- .


26/236

26 RATE OF FLOW METERS

Turbine [lowmeter typically used inpetrochemical, offshore gasand oil processing nuclear and power generating industries.

The frequency range is from 3 to 10 Hz. The magnitude of the voltage isapproximately proportional to the flowrate. At rated flow it is usually 10 to1000 mV rms. The signal is normally shaped to a square wave which is thenamplified. The number of pulses per unit t ime can be determined by means of adigital counter to give a digital speed of flowindication. Alternatively, the numberof pulses per unit t ime can be conver ted to an analogue of the pulsing rate.The turbine meter isbasically a speed of f lowmeter, although it is quite easy toobtain volume rate or mass rate bymultiplying the f lowrate bythe f lowarea and bythe density of the liquid.A very wide range of associated electronic equipment is available fromflowmeter manufacturers and electronic instrument makers . This associated

equipment includes totalisers, batchers, analogue outputs, recorders, computers,linearisers etc;High frequency turbine flowmeters have the advantage of greater digital readout resolution for a given sampling period. The number ofpulses per revolution canbe increased by mounting a rim on the turbine in which a number of ferrit es areembedded (Figure 2), or by using a slot ted rim as shown in Figure 3. For evenhigher resolution, multiple pick-ups can be used (Figure 4).Ifa turbine meter is required for an application where it willbe regularly testedby means of a meter prover, it is important that a meter should be selected with ahigh pulse resolut ion. The physical l imitations to the number of blades, or to thenumber of buttons that can be placed in a r im, might make it imposs ible to obtainthe required resolut ion, in which case use can be made of phase interpolationtechniques. See Meter Provers.A typical shape of the output curve of a turbine flowmeter is as shown in

TURBINE FLOWMETER'

WHICH F L U ID S Y S T E MM E A S U R E M E N T D OY O U N E E D ? ~~t

ft:,41Fors ing le or mu l tip le -input d ig ita l readoutsa nd a f ul l ra ng e o fcompat ible sensors ,t al k t o Webs te rIns truments . Wedesign, manufacture,expor t wor ldwide .Our equ ipmenti s u sed i n f i el dand labora torytest ing ,on hydrau l ics y st ems , p ro cess and se rv ic e l in e s.

P l ease cont ac t u s f or mo re i nf ormat io n .D F S E R IE S F LO WREADOUTT ea me d w it h o ur f lo w b lo ck s, t om ea su re f lo w fr om 8 0 cc's 1m i n t o800 I Im in a t p re ss ur es t o 420 bar.DPSERIESPR ES S UR E R E AD O UTCa l ib r at ed f o r p r es s ur et ra n sd u ce rs u p to 700 b ar o r10,000 psi.DTSERIEST EMP ERA T UR E R E AD O UTC om ple me ~te d b y w i de ra ng e o fs en so rs w hi ch c an b e I ns ta ll ed i nh i gh p r es s u re s y st ems .D S S E RI ES S P EED R E AD O UTC on ne cte d t o W e bs te r p ic k- up s tor ea d s ha ft o r g e ar w he e! s pe ed .F a st u pd a te t im e .

DMSERIESM U LT IP L E I NP U T R E AD O UTM e as ur es p re ss u re , p e ak p re s su re( he ld i n m e mo ry ), fl ow a ndt em p er at ur e. P e n r ec or de r o u tp u t.SENSORSF u ll r an g e, i nC l ud in g t ur bi ne a n dp o si ti ve d is pl ac em e nt f lo w b lo ck sp r es s ur e t ra n s duc e rs , t empe ra t ur ep r obes and t a chomet e rs .

...... WEBSTER INSTRUMENT::WA DIVISION OF WEBTEC PRODI..JCT$ UMrTE;!West Newl ands Indus tr ial Es ta te Somersham Cambr idgesh ir e PE173E.Tel : 10487)842202 Fax : [0487] 843104Telex :32781

----._----- ...._


27/236

TURBINE FLOWMETERSPut Daniel nowmeasurement experience to work on your specific problems.

~ULTRASONICFLOWMETERSMultlpath c u s r o d v t ra n s r e rg as f lo wm et er l ic en se d b yB ri ti sh G a s. N o p re ss u red ro p , n o m o vi ng p ar ts . d oe sno t need , ndi v idua l we tcanoration." Large t u rn -d ow n r at io . a nd w id e r an ge -a bi li ty . B i- d ir ec ti on a l f lo wmeas u rem en t S el f c h ec k in g

2500 SERIES MAINS- i ~ OWERED RTUICOMPUTERSS pe c if ic a ll y E ur op e an . u se r-con li gur abl e . I SO equat ions(also AGA. AP I, NX, etc. IMedi a- in de p en d en t l or r em o teo pe ra ti on " W id e r an ge o fc ompen s at io n/ pr oc e ss in g . U pt o 16-br t r eso l u ti on.

DANALYZER BTU-CONTENTCHROMATOGRAPHSOn- li ne. au t omati c ana lys is .M ul ti pl e c ol um ns l or f as treadout. Self -cal ibrat ing.R emo fe o pe ra ti on o v er a n yc ommuni ca ti on m edi a R e pe a ts'";IB TU i n 1000 dynamicallyover ift o t 30 - F r an g e.

ORIFICE PLATESAND FLANGE UNIONSP lat es o f fe r h i ghes t accur acy ,l on g es f l il e. R e co g ni ze d s u pe ri or .F la n ge U n io ns c on fo rm t o c o d e s.A lm os t a Usees. pressures.

SENtOR' ORIFICE FITTINGSE as y , r ap id c h an g in g o f o ri fi cep l a tes w i fhou t i n te r rup t ingl in e f lo w . L iq u id s a n d g a se s .Oldest a n d b e st "Senior" available.

II

Inquire about other Daniel products-and let our half-century-plusexper ience help solve your problems,LIQUID TURBtNE METERSl a rg e -v o lum e c u st od y t ra n s-fer 1" ' to 24' I n c l a ss t 5010600. no 12' in class1 5 01 0 15 0 0. C a n b e fi tt edfoc bi-directional flow D AN JEl lN D US TR IE S Lro .tecnlands I ndus tr ia l E s ta t etarbert, Slirlingshir.Scotland. fK5 3NSTel: (0324} 556!flTelex: 779634 DANFAl GCab le : DANIEL FA lK IRK

l ib ra ry H o us eThe GreenOatchet.SloughB e ,k sh ir e, E n gl a nd S K3 9A UTel: i 0753) 4 8587

--- - - ~ 'C ._ '_ .~ ~ ~ _1111'":._-INDUSTRIES, L TOc

THERMALPULSE nLIQUID FLOW METERFor Process Streams 0.1 ml/min to 100 ml/min No Moving Parts; All Glass and Teflon Prec is ion Bett er than 0.1% of Fu ll Sca le RS-232 and 20mA Computer In te rf ace Programmable 0 to 5Volt Analog Signal 4 Alarm Relays: S_P.D.T. Rated at 5 AMPS 16 Character Display of Flow or Volume$2950.00The Thermalpulse I I f low measuring system is a- microprocessor based flowmeter designed tomeasure flow rates from 0.1 ml/min to 100 mllmin with a precision 01"0.1%.

The flow cel l's maintenance free design of no moving parts is also chemically inert to most solventsystems hailing Teflon, glass and Kalrez the only materials wetted by the stream. The flow cel ls areless than 4" long and are f itt ed d ir ec tl y i nt o t he s tream's p lumbing sys tem requir ing no specia lorientation, mounting or location.The Control Un it p rovi des the i nt erface fo r the flow cel l and provi des the user wi th a vari et y o foperat iona l modes and d ispl ay cho ices a t t he touch of a key . The Cont ro l Un it communicationfeatures include anRS-232 and 20mA current loop for computer communications and data processingsystems. A programmable 5 vo lt D.C. analog s ignal makes recordi ng and cont roumq a s imp leaddition. The performance and flexibility of the Thermalpulse II has made it an indispensible tool forChromatographers, Quali ty Control Engineers, Process Engineers, and Scientists involved withResearch and Development.Carl our tol l free number or write for more information. 'TenOOarn3~~f( !~~~I~~ edUBd emltr~~~~Jci..~~~~~~IMO. "T EK I Molytek,Inc. 2419SmallmanSI.,Pittsburgh,PA 15222,U.S.A_... T Telephone (412)261-903ti Telex 812-569FromOutsidePennsylvania(800)245-5101 FromCanada(BOO)41-8197..._._" ._-_._...---------~----.-~-----

TURBINE FLOWMETERS

Hydroturbine flowmeter used for monitoring control andoperational testing of hydraulic systems,

Rimmed rotor

Unit volumeper pulseBut to ns - made o fHi-Mu80, ahigh-permeabilitysoft iron alloy

Figure 2Rimmed rotor with embedded paramagnetic buttons.

27

__------- --_- ---------" ...__"-- .---


28/236


Figure 3 .Slotted ring for high resolution turbine meters.

Single pick-up - 4 pulses per TOtorrevolution

f-- 36 00__j_j\, EI:C_t_riC_a_I_ !\, I\ I\ I\

~ Two pick-ups - 8 pulses per rotor revolution~ / 1 _ . . 360 _

13 ~ectricallCoil No.2

Coil No.1_j\,\,, '

- - l 9 0 QE ~ 3 6 O " E - - - - j_J\, .:1I I\

Coil No.2

Figure 4 .. .Multiple pick-ups for sti ll higher resolution.

IJIiI

TURBINE FLOWMETERS 29

Fully turbulentRegionLaminarRegion

FlowrateFigure 5Typical turbine f lowmeter Cd curve showing low rangenon-linearity.

Figure 5. The curve shows the K-factor against flowra te. The K-factor, is therelationship between the number of pul ses produced by the flowmete r, per uni tvolume.The shape ofthe character ist ic isdependent upon the parameters of the l iquidmetered, mainly its viscosity, it isalso dependent upon the f low range covered bythe flowmeter.The curve consists of a l inear and a non-l inear section. The non-l ineari ty of thefirst section isdue to bearing friction, magnetic drag, velocity profile, viscous dragof the impeller tips etc. The effects of the resistive forces on the turbine areparticularly not iceable in the smal ler size meters of 50 mm (2 in) bore and less,where they can represent a considerable proportion of the driving torque.The error due to magnet ic drag from the pick-up can be avoided by the use ofnon-magnetic pick-ups. For instance, capacitance pick-up, or an optical-pick-upwhere a light shines, via an optical fibre, on to the turbine; each time a blade passes,the light is reflected and a signal isgenerated. Itis also possible to have non-dragpick-up by applying a high frequency carri er signa l to a pick-up coil, using anoscillator. The rotor blades modulate the carrier signal at a rate which is

proportional to the turbine speed.These non-drag type pick-ups are not in general use as they require an externalpower source and are mostly used on lowflow flowmeters,The error due to bearing friction has been minimised by the generalimprovement in bearing des ign and also by the use of hydro-dynamic bearings,ie floating rotors see Figure 6,al though these tend to increase the sensi tivi ty of theflowmeters to viscosity changes.The major source of error, without doubt, arises from the viscosity of themetered fluid as viscous drag takes place between the hub of the turbine and thebearing hub and between the turbine blade extremities and the flowmeter housing.At the top end of the flow range, it is permissible to exceed the maximum flowby 50 to 100% for short periods, although this will reduce bearing life. Themaximum flow is mainly limited by pressure drop considerations and cavitation.


29/236


BearingassemblyDeflector(upstream)

l Sydraulicbalance point

\ Impingementannulus

IiII

IDownstreamforce

Deflector(downstream)

Rotor

IA.\

\ \B. C.

\i

Pressure distribution

Figure 6 . .'Floating' rotor prmnple.

The shape ofthe curve depends upon the viscosity of the liquid which va~~s;i~htern era ture and from liquid to liquid, aswel l as on t~e flow range over w IC t efl Pt ed Turbine flowmeters can be designed so that they are lessowme er IS us . . b db'sensitive to one of these two factors than to the other. This can e one y vary~ngth ti clearance ofthe impeller, bycorrect des ign ofthe rotor bla?es, or bya~tenngth~ ~~b/rotor ratio etc. The effect of increasing the tip clearance IS tw


30/236


I t is important that the speed pick-up of the axial ly aligned rotor isof the non-drag type, particularly as it is the error sensing rotor.In operation, the fluid entering the flowmeter will cause the heli cal rotor torotate at an angular speed which isproport ional to Vtan.A inwhich V is the speedof f low and A is the mean helix angle of the turbine rotor blades.Three examples are:(a) In the case of an ideal fri ctionless operat ion, the fluid should issuefrom the helical rotor asaxially as i t entered, and the second axial lyaligned rotor should not rotate.(b) In a pract ical case where bearing frict ion and viscous drag retard thespeed of the helically bladed rotor, a swirl component of momentumwill be gained by the f luid passing through this turbine. The secondaxially bladed turbine will sense, however, the swirl of the fluidpassing through it and provide a corresponding speed s ignal. Therotational speed of the second rotor will thus be equivalent to the

speed lost by the first turbine. A complete indication of the flowpassing through the flowmeter willbe obtained bythe addition ofthespeed signals of both rotors.(c) In the case ofextreme frict ion, the f irst rotor will be s tationary. Thesecond rotor willthen rotate inopposition to the tendency ofthe firstrotor and at a speed equivalent to that of an unimpeded first rotor.In all cases there wil l be viscous drag effects on the second rotor , so that therewill be a small error on the error correct ion signal , but overal l the improvement inaccuracy issignificant. This flowmeter isagain shown in Figure 8, where the largernon-drag pick-up can be seen clear ly. The second rotor can also be given a smallhelix angle.

Flow range and rangeabfhtyTurbine flowmeters are available to measure flow rates from as low as Ollitlmin.to as high as 200 000 lit/min, These flowmeters are available with rangeabilities of3:1 to 10:1for l inear range, and 20:1 to 50:1 for extended range. The whole outputcurve of a turbine flowmeter can be linearised by using a microprocessor,programmed to apply correction factors.AccuracyA turbine flowmeter gives a very repeatable output. If all possible variables aremaintained cons tant , a repeatabil ity of 005% of a point can be achieved. Anaccuracy of 015% of a point isnormal, while with care, accuracies of 010%of a point can be achieved. Generally speaking, the larger size flowmeters are moreaccurate.ApplicationThe turbine meter is ideal , i f the l iquid to be metered has a viscosi ty which is lessthan 500cSt for larger f1owmeters, and 200 cSt for the smaller flowmeters which fora particular application, isconstant to fairly close tolerances; and an accuracy intheorder of 015% over a 10:1turn down ratio is required.The turbine flowmeter is used in aerospace, petro-chemical and oil industriesand also for custody transfer ofexpensive liquids. It isused inbatching, mixing andhygienic appli cations such as in breweries, di sti lleries and dai ri es, where theflowmeters can be steam cleaned, and in cryogenic applications in road tankers forliquid gas deliveries.------------- ------- --_---

III


Figure 8Double rotor flowmeter shOWing the large'capaci tance type' p ick-up for the second rotor.

An int~rest ing applicat ion isshown in Figure 9, where a turbine f lowmeter ismounted Inthe handle of a dispensing nozzle.. T~e turbine f lowmeter has a quick response time as the rotor has low inert ia andIS SUitable for measuring f luctuating flow. For pulsating flow digital read outshould be used and the counting period should be long compared with thefrequency of the flow pulsations. '. If the f low is in ~he form of one jet , for example while measur ing a shor t single~hscharge, t?e pulsIn~ rate of the flowmeter should be high. Bearing wear isusuallyIncreased With pulsating flow.Turbine flowmet~rs are extensively used for the metering of gas flows, but veryseldol? for mea~unng steam. Table 1 gives typical examples of the airflowcapaclt.les of turbine fl~wmeters compared with liquid flow for flowmeters of thesa~e s ize. Meters re9ul~ed for the measurement of gas f low are usually speciallydesigned for gas applications,

----.~--~----


31/236

RATE OF FLOW METERS

Flanged turbine meter.

Figure 9A small turbine f lowmeter with digital read-outmounted in the handle of a dispens ing nozzle.

The driving to rque exerted by the gas on the turbine i smuch smalle r than thatexerted bya liquid. This torque isproport ional to pv',where p is the densi ty of thef luid and Y the speed off low. To increase the speed off lowin order to increase thedriving torque, the hub ofthe turbine ismade much larger for gas meters than forl iquid meters. The rotor should also be as l ight asposs ible.Turbine meters for gases are not ava ilable in the smal le r si zes, because thebearing friction becomes proportionally large. The range of gas meters isinfluenced by the density of the gas, which isproportional to its pressure.The density of the gas and thus its pressure , will affect the cal ibra tion of theturbine meter. There are no calibration facil it ies in which the calibration can be

carried out over a range of pressures.

TURBINE FLOWMETERS

" ' ' ' " ' " " '~MV). 9 B B . 8If){f')f''')1fl9~t;l6000

EE

35


32/236

RATE OF FLOW METERS36

Turbine meter for g a $ S

Influence of the fluid parametersTurbine flowmeters are suitable for most liquids including cryogenic liquids, acids,petrochemicals and chemical liquids. They are less ~uitable for liquids which tendto foam or liquids which contain gas, as the meters wil lmeasure the total volume ofliquid plus gas.These f10wmeters are not recommended for liquids with viscosities of more than200 cSt for small f1owmeters, 500 cSt for large flowmeters, because the accuracy ofthese f10wmeters isaffected by changes in viscosity.The bearings demand that the fluid isfiltered. For plain bearings a small amountof contaminant is al lowed and filt ration should be to 70 microns. For some highspeed baI l bearings, f il trat ion above 10 microns is advised. Preferably the f luidshould have lubricating properties.If a flowmeter is cal ibrated with water, an increase in vi scosity will tend toincrease the non-linear first section of the calibration curve. Reduction of densityalso has this effect.A common mistake made is to assume that ifa turbine f lowmeter (or any otherflowmete r) is to be used wi th avia tion fuel such as AVTAG, i t wi ll always givemeaningful results when used with any other batch of AVTAG. Depending on thesource of supply, the vi scosity and density of these fuel s can vary wide ly. Al lparameters of the calibration liquid should be specifie~; this means densi ty andviscosity and, therefore, also its temperature and sometimes pressure.

The precise metering of flow with turbine flowmeters requires a knowledge andcontrol of all parameters which inf luence the performance ofthe f lowmeter, bothduring the calibration and in its application.The inf luence of the parameters varies among the different makes and s izes off lowmeters. The inf luence of f lowrate and viscosi ty on the calibration factor isgenerally greater with the smaller size flowmeters.


As the viscosi!y of oils.etc is temperature dependent , a correct ion should be~ade, or alternatively a twm-rotor turbine meter should be used ifthe temperatureIS not constant.Operating conditions - pressure and temperatureThere is a minimum op~rating pressure which will prevent cavitation occurring at~heoutlet end of a turbine f lowmeter. This should be (3dP + 13Vp) inwhich dPIS the pressur~ loss ac~ossthe flowm~ter and yp isthe liquid vapour pressure. Thepressure loss III a turb.me flowme~er IS approxl.mately proportional to the square of~hef1o~rate and .alsoincreases Withthe VISCOSity.f the fluid. Normally flowmetersare designed togive a pressure drop of3 to 10lb/irr 'when used with water at a ratedflow.For other liquids, the pressure drop across the flowmeter can be estimated bytheformula:dP =PD X 11-0.25 x SGO.75where1 1 - = viscosity in cPSG = specific gravityPD = pressure drop for waterGenerally speaking, turbine flowmeters are easy to design for high pressures.

Installation conditionsIfthe flowmeter ism~unted at an an~e, be~~ing load ischanged and accuracy canbe.affected. The turbine flowmeter IS sensitrve to velocity profile changes and toswirl,. General~y '.misalignmen~s, T junctions, upstream and downstream valves, poorplpe.work f it ting and mult iple bends can introduce a distor ted velocity profi levortices and swirl :-vhichhave a pronounced effect on the flowmeter output. Swirlgenerated by multiple bends persists over a considerable length.An optimum ins tallat ion is where a fully developed profi le is attained beforeentr~ t? the f1o,:meter. Swirl should also be removed by using a flow straightener.DevlatJ~ns of.2 Y o and more caused by swi rl have been observed. The best flowpattern IS obtained byusing adequate length ofs traight piping (10 D upstream 5 Ddownstream), as well as a flow straightener (Figure 10). The flow through theflowmeter should always be controlled by means of a valve mounted downstreamof the flowmeter.

Coil protection box

Meter and straightener connections

Figure 10Typical flowmeter installation.

~I


33/236


Figure 11Pre-calibrated, field replaceable rotor, assemblycapsule.

CalibrationIfaccuracy isimportant, turbine flowmeters should be calibrated using exactly thesame fluids which are to be measured, ifthis isnot possible, some correction factorshould be derived.Calibration should also be carried out using the same upstream and downstreampipework aswould be used in i ts ins tallat ion. This often means that cal ibration hasto be carried out on s ite using a meter prover.If a secondary s tandard is used for cal ibration, this secondary s tandard shouldnot be sensi tive to f lowprof ile and swir l in the same way asa turbine f lowmeter , forexample a posi tive di splacement flowmeter should be used as the secondarystandard.

Turbine flowmeter.


MaintenanceBe~rings need regular servi:ing or replacement. For this purpose the flowmeter hasto e removed .from the l ine, Pre-ca libra ted, fi eld rep laceable rotor assernblc~psules are avail~ble for some flowmet:rs (Figure 11). However their calibratio~WIll ?ot be to ~ptmlUm accuracy. Expenments are being carried out with var iousbeanng matenals for f lowmeters used with chemically aggress ive f luids Goodresults were obtained with stellite and with carbide bearings. .

Turbine meters for the food and beverage industries.


34/236

41

Pelton Wheel and other PropellerFlowmetersTHESE FLOWMETERS use a mult i-blade rotor from which the s traight bladesprotrude radially (Figures 1 and 2). The f low through the f lowmeter, isnarrowedto a jet which enters the f lowmeter chamber tangentially and makes impact at r ightang les with the blades. The rotor i s d riven at a speed which i sp roport iona l to thespeed of flow.

Pelton wheel flowmeters are suitable for extremely low flows, they are also usedas bypass fIowmeters (see Shunt Flowmeters}.

Figure 1Pelton wheel flowmeter.

Bearingless Hover type flowmeterThe bearingless meter or Hoverf/o shown in Figure 3, was special ly des igned tosurmount the problem of bearing weakness encountered with most turbine typef1owmeters.This f lowmeter was developed by using a mathematical model based on airfoiltheory. Liquid enters the flowmeter body chamber from the inlet port. Thischamber contains a removable cartridge which encloses a rotor. The rotor consistsof a tu rbine and a lower di sc posi tioned at each end of the cent ral shaft . Withoutflowthe rotor rests on the top hover seat. When flowcommences, the pressure drop

---- ... _ .._----- --- _ _ _ I


35/236


Tip mountedIerrites

~ Outletoensingcoil l . . = = = = : : : = : ~ = - - : : : : : = = : : : : : : J '"nletip mounted ferrites '"utlet

MM:OrificelPellon

Figure 2 . h I ge capabil it y down to 002 l it /min and showing theFullf low Pelton wheel flowmeter Wt ow ranflowmeter used as a shunt flowmeter.

Pelton wheel flowmeter.

across the lower hover disc l if ts the rotor . The liq~id f lowflPasses t~rough bothturbines causing the rotor to turn at a speed proportional to ow spee . bi. bl 1 t ce pick up system as used on most tur meIt has a conventional vana ere uc an ~ lses per revolution andtlowmeters. The increased number of magnets give more putherefore greater resolution.Propeller tlowmeters . . bine flowmeters but the propeller isPropeller flowmet~rs are slmIl~r. t.o t~~r~ue to a counte; mechanism, thereforedesigned so as to give adequate r~v~g eters This type of flowmeter is mainlythey are volume rather than spee ow~ .used for measuring large water consumptlon.

----_ ..__-------__-----------

PELTON WHEEL FLOWMETERS

Litre Me ter Flowme ters

Flowrates from 0.01 to22,000 litres/min.

Pressures to 300 bar. Temperatures to 135cC .

Litre Meter Limi ted50 / 53 Habans CloseRabans Lane Industrial EstateAylesburyBuckinghamshire HP19 3RSTel (0296) 20341 Telex 837801

The precision Pelton Wheel turbine is theheart of all Litre Meter Flowmeters. It runsin sapphire bearings for accuracy and isproduced from a range of chemical lyresistant materials for a long l ife.There are two types of Litre Meterflowmeters. In the LM Series, designed forsmaller f lowrates, the enti re f low is di rectedonto the rotor. A sensor detects ferri tes inthe rotor tips to produce a pulse outputThe larger MM Series combines an orificewith an identical Pelton Wheel assembly,mounted in a by - pass chamber. In bothtypes of meter. the pulse output is directlyproportional to flowrate.Litre Meter also supply a complete range ofelectronic instruments for flowrate indication,totalisation, batching, alarm, data loggingand control requirements. Specialistinstrumentation with programmablelinearising facil it ies is also available . Meter bodies are provided in 316stainless steel and other corrosion-resistant materials, including anal l-PVC version with no metal parts. Sizes 6 to 300mm (% to 12") borewith screwed, hose, or flangeconnections.*LITREMETERFLOW MEASUREMENT SPECIALISTS

----.__-- .


36/236

PELTON wHEEL FLOWMETERS

Compact, l ightweight andself-powered. Non~intrusive transducersfor aUpipes. Quick, computer-aidedset-uo . S imple. Enter 00,10,pipe material. Automatic compensationfor other variables. Clear or c loudy l iquids- non-Doppler,

Direc t LCD readout o f l inear,volumetric or total f low. Instant chanqs-over betweenmetric and Imperial units. Good for cash flow too. Around 1500 in UK complete.

National Weights and Measures LaboratoryThddington, Middlesexfor Calibration of Flowmeters and VolumetricStandards traceable to National Standards.

Flowmeters up to 6000 l/min.On site Calibration of Proving Tanksand Liquefied Petroleum Gas Systems.

Service throughout the U.K..------------.-~-~-

,I

PELTON WHEEL AND OTHER PROPELLER FLOWMETERS 43

Figure 3'Hoverflo' bearingless turbine type flowmeters.

300 bar, h igh pressure Pel ton wheelflowmeter.

--~--.~--. _ I


37/236


Pel ton wheel PVC f lowmeter speci fi call y des igned to handleaggressIve acids.

Figure 4Propeller flowmeter.

)).....?-'"'_ '. ~,."

.,.~? ..,-~"'''J< > .. . >

Diagram of propeller f lowmeter shown inFigure 4.There is a glandless magnetic coul!ling betweenmeasuring unit and drive mechanism.

. __ _ _ .OO "_ __ __ .o O . _

PELTON WHEEL AND OTHER PROPELLER FLOWMETERS 45

The propeller can bemounted on a vertical axis(Figure 4) oron a horizontal axis(Figure 5).In the vertical arrangement, the upward flow of the liquid reduces thrust andwear on the lower bearing, but the vertical type has a larger pressure lossthan the

horizontal type.Other impeller type flowmetersThere isa large variety offlowmeters inwhichan impeller or turbine isdriven roundby the fluid flow; many of these are used as watermeters such as the multi-jet

Series 71 with read-out type L3/T.

Figure 5On this version the impeller spindle isconcentric with the pipe axi s. The waterflow is straight through the flowmeter andtherefore causes minimum head loss.

-------


38/236


>>

Multi-jet propeller flowmeter; the liquid passesthrough the small holes in the f lowmeter chamberand impinges on the rotor .

Flowmeter manufaCtured from pvc fo r u se in corrosivefluids.

Body

Spiral enclosed water meter.

PELTON WHEEL AND OTHER PROPELLER fLOWMETERS 47

flowmeter as shown in Figure 6. In the multi-jet flowmeter the liquid enters theflowmeter chamber through a number of tangentionaJ orifices.Another example of an impeller type flowmeter isshown in Figure 7.

F igure 6'ulti-jet flowmeter.

Figure 7Water flowmeter with direct drive for counter.

------~ ~----~- ~


39/236

RATE OF FLOW METERS

~!;;:d8propeller f!0wmeler, allowing easy removal ofpropellerassembly for servlcmg,

Angled propeller flowmeters 11 fl eter in which the propeller can bengled prope er owm 'd'Figure 8 shows an a b 'ned or replaced thereby avoi mg any, h it needs to e exarm '.'removed sIdeways ~ e~I 'The rotor bearings are located outSIdethe mamdisturbance to the pIpe Installation. inatedflow and are lessliable to become contamInate '

fjjf

49

Target or Dragplate FlowmetersTHE TARGET flowmeter consists of a cylindrical tube with an obstruction in theform of a thin discmounted inside, The discis attached to the end ofa cantilever,which, in turn, is mounted in a protrusion of the meter body (Figure I), Theflowmeter measures flowin terms of dynamic forces acting on a fixed body in theflowstream.

Force y22gCd A P

whereCd drag coefficientA target areap fluid densityy velocity

Tests are necessary to establish Cd.

Figure ITarget [lowmeters.


40/236


Target flowmeter with retract-ableprobe for open stream flowvelocity measurement.

\+.:- gg .

This flowmeter was developedspecifically for precise measure-men t o ff low o f d irty l iquids, gasesand slurries.

TARGET OR DRAGPLATE FLOWMETERS 51

The force which the flow exerts on the obstruction causes a bending strain in thecantilever. The level ofthis strain ismeasured with a strain-gauge and isa measureofthe fiowrate. Alternatively a displacement transducer can be used to measure theamount of rotat ion ofthe pivot point of the lever . The rangeabil ity of this type offlowmeter isabout 10:1.The range can be changed bychanging the target.Target flowmeters are frequently used to measure pulsating or transient flows.For this purpose the electrical meter output should be linearly proportional to flow.Itis then quite easy to process the output and obtain average f low.The advantages of this type of flowmeter include high response, no movingparts, bi-directional, long life, low pressure drop and easily calibrated.Typical applications for dragplate or s tatic plate type f lowmeters are given inTable L Flowmeters based on the principle shown in Figure 2 can be used

TABLE I-STATIC PLATE FLOWMETERS

,.~_

Applications (extract)Industry Functions Industry FunctionsAtomic power Controlling cooling and Mf condensers Cooling circuit controlstations lubrication circuitsBoilers Prevention oflow water Night storage Prevention of l ow waterlevels heater systems levelsOxygen cutters Burner control Paper machines Cooling and lubricationcircuit controlChemistry Flow control Pumps Prevention of runningdryDiesel engines Leakage, oil and cooli ng Tube generat ors Cool ing and lubricationwater control circuit controlGenerators Cooling circuit control X-ray plant Valve cooling controlHeating plant Preve nt ion of low water Forge he at in g p lan t Coi l coo ling cont rollevelsHigh pressure Prevent ion of low water Welding machines Cable cooling controlpurifiers pressureHydraulic Flow control Heavy machinery Lubrication circuitmachines and controlplantInduction Cooling and oil circuit Relief valves Response controlfurnaces controlCompressors Cooling and oil cir cui t Vacuum furnaces Jacket cooling contr olcontrolArcfurnaces Cooli ng cir cui t control Machine tool s Emulsion and lubrica-tion circuit control

~.---- ...~---- -------------


41/236

52

Figure 2Diagram of target flowmeter giving directflow indication.

RATE OF FLOW METERS

1.Paddle or static plate.2.Spring.3.Bellows.4.Pointer.5.Scale.6.Microswitch.7.Indicating lamp.

throughout heavy indus try, in rol ling mills, the c~em~cal and. pharmaceuticalindust ry, food and beverage industry and the machme mdus~ry In gen~~al. Oneadvantage ofthis type ofmeter des ign is that i t~anbe mounted I~ ~ny position. Theinstrument must be calibrated in accordance with the actual posmon however.

53

F l u i d i c F l o v v u n e t e r sORIGINALLY DEVELOPED in the ear ly nineteen seventies,fluidicflowmetersconsist of a f luidic oscil lator. The oscil lator consists of a jet which attaches i tself,due to the Coanda effect alternately to oppos ite walls (wall attachment) of theflowmeter body. The Coanda effect is explained as follows: if the wall of thef lowmeter body s lopes away from the jet asshown in Figure 1, the pressure in thespace between the jet and the s idewall drops below the pressure at the other s ide ofthe jet due to turbulence. Consequently the jet will be deflected against thesidewall.

Jet

Turbulence causinglow pressure regionFigure 1The turbulence near the wal l causes a pressure drop across thejet which forces i t towards the wal l to which i tw i ll attach i tsel f.

The shape of the f lowmeter body allows for the f lowing s tream to attach itself atrandom to one of the sidewal ls when flow is initi ated. At a point downstream, asmall por tion of the f luid is diver ted through a feedback passage to a control por t(Figure 2). This feedback flow acts against the main flow and diverts it to the

.~---_ ._-_ .


42/236

S4 RATE OF FLOW METERS

Control port Feedback pas sage

Figure 2

opposite wall where the same feedback action is repeated (Figure 3). The result isa continuous self-induced oscillation of the flow between the sidewalls of theflowmeter body. The frequency of this oscillation is linearly related to the fluidvelocity and hence the volume flowrate.

Figure 3

The oscillations are detected by a flush-mounted sensor and are amplified byelectronic means to provide a digital output.The flow velocity in the feedback passages varies continuously from zero tomaximum; it provides a region with substantial flowrate change in which it is easyto sense the frequency of oscillation, and produce a relatively noise free output.Only one of the feedback passages needs to have a sensor.The sensing element is normally a thermistor which is part of a constant

temperature Wheatstone Bridge. The other sections of the bridge can be remotelypositioned (up to 300 m (328 yd)) in a control room. The bridge output isconditioned and amplified to provide an indication of flowrate and total volumepassed.Fluidic flowmeters will operate at much lower Reynolds numbers than mostother flowmeters, although flow ranges depend on viscosity. The rangeability,which is typically 30:1, decreases with increasing viscosity. These flowmeters arevery suitable for viscous liquids such as fuel oil, For a given flowmeter size, the:

- ~ .~ ..... -~.~~.-.-.~----

FLUIDIC FLOWMETERS

600S8 05 6 0~0 S4 0~"n S2 0'3~. . . . 500~.s 48 0~ 46044 042 0

5 5

TABLE 1- TYPICAL CALIBRATION FACTOR FOR FLUID FLOWMETER

- - e- -- -

+2% of rate band. . . . . . . . . ,r - . . .

1T

40 0 00 1Normali sed f low Flow rate gallminViscosity (centistokes)

The graph shows a typical performance curv e" The shift in 'K' faReynolds number approaches 600 The normaf d fl I ,c tor at low flow rate s occurs as the pipe(c en ti st ok es ), a nd is d ir ec t r ea di ng "i n g al /m in f o; :a te ow ~ca e l~ sh' .'w~ as galrrnin + kinetic viscosity60 "F. The meter'S pe rformance on other fluid be r , WI o se viscosity IS a pp ro xima te ly I c en ti st ok e a tII . , . " s can eva uated by dividing " ISfl (i "OWI~gVl~lty (In centistokes) and entering the graph at the I I d I ow_rate III gal /min ) by i tsvanation InK f ac to r c an b e e va lu at ed t o d et erm in e if th ca cu ale . value. In this manner the expe ctedexpected opera tinz ranee. e meter WIll gIVe the required accuracy over the

Figure 4Fluidic flowmeter for high viscosity fluid"

systemw,il!0I:'erate at muchlower flows than conventional flowmeters Electro .repeatability IS said to bewithin 02% of actual flowrate. . rueThe fluidic flow~et~r s~own in Figure 4features dual output signals, analo ue

f 1 0 : - v control and/or indication and scaled pulse for direct totalising in enginee~ngunits.


43/236

57

Electromagnetic FlowmetersTHE MEASURING principle of the electromagnetic flowmeter is based onFaraday's law of induction. If a conductor is moved within a magnetic field. avoltage is induced at right angles to the direction of movement in that conductorand at right angles to the magnetic field. See Figure 1.This voltage is proportionalto the average speed at which the conductor moves. In these flowmeters themagnetic field is produced by a pai r of coils (see Figure 2) and the conductor isrepresented by liquid which must be electrically conductive. When the liquid flowsthrough the magnetic field, it cuts the lines of magnetic force.The induced voltage ispicked up by two insulated electrodes embedded in thewall of the f lowtube and which are incontact with the flowing fluid .The voltage generated (E) is:E = B.L.VwhereB is magnetic inductionL is length of conductorV is velocity of conductor

v

Figure IDiagram of electromagnetic flowmeter. _ J


44/236


Figure 2Diagram of electromagnetic flowmeter.

Electrodes

Electromagnetic

Figure 3 .Diagram of electromagnetic flow measurement unit.

The length of the conductor L corresponds to the ~ist~n~e.between thed is therefore constant. The magnetic induction B IS a fl?wmeter~!~~~~~~~~~uced signalvoltage is proportionaldto th~~ve~~~ea~~;t~~l~~t~~~c~~;fl file over the whole flow area, an so 1 IS .~~~fil~~b~~~ity does not enter into the flowmeter equation and electromagneticflowmeters are true speed flowmeters.

ELECTROMAGNETIC FLOWMETERS

An electromagnetic flowmeter system consists of a detector head, a converterand a display (Figure 3). The detector head consists of a tube made from a non-magnetic material. If the tube ismade from metal it willhave an insulating liner.Two electrodes are mounted in the tube and make contact with the liquid beingmetered.

Electromagnetic flowmeter withintrinsically safe circuit.

Polarising potentials can be detected across the electrode when theelectromagnet is off. This is caused by various effects and would causemeasurement errors if a direct current was used for excitation. To avoid thesepolarising potentials an a.c. excitation voltage is used to generate the magneticfield.a.c, ExcitationWhen using a.c. excitation, the output is also an a.c. voltage from which d.c.voltages can be separated. Various forms of a.c. excitation can be used, such assinusoidal, square wave trapezoidal etc.Sinusoidal excitation produces an unwanted transformer voltage which is

induced by the varyingmagnetic flux linking a loop of the electrode lead. This canbe overcome partly by providing an artifical loop on one electrode. Thetransformer voltage is proportional to the frequency of excitation. This frequencyistherefore usually kept low, in the order of 50Hz. This transformer voltage mustbe cancelled out by the system's electronics.

----- ._- --------___-------


45/236

RATE OF FLOW METERS60Square waveand other excitation wave forms are used to avoid the problems of

transformer voltages. Quadrature voltages out of phase with the signal are rejectedbythe converter. Those in phase with the output signal are eliminated bya zero~ngfacilitv of the converter. Zero adjustment is made at no-flow. The factors whichcontribute to the zero error may change during service and occasional re-zeroing isnecessary.In some continuous processes it isnot possible to shut down and interrupt theprocess to carry out this re-zeroing. To overcome this problem and, at the sametime, to avoid the technical problems associated with eliminating quadraturevoltages in the converter, pulsed d.c. excitation was developed. Electromagneticflowmeters withpulsedd.c. excitation are nowavailable frommost manufacturers.Bipolar pulse operationBipolar pulse operation isused by one manufacturer as a means of eliminating thezero error (Figure 4).Under ideal or reference conditions th

fluid flowmetering

Documents