THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 346 E. 47th St., New York, N.Y. 117 93-GT-7 The Society shll not be responsible for sttements or opinions dvnced in ppers or discussion t meetings of the Society or of its Divisions or Sections, or printed in its publictions. Discussion is printed only if the pper is published in n ASME Journl. Ppers re vilble from ASME for 15 months fter the meeting. Printed in U.S.A. Copyright 1993 by ASME COMPARISON OF CORIOLIS AND TURBINE TYPE FLOW METERS FOR FUEL MEASUREMENT IN GAS TURBINE TESTING J. D. McLeod nd W. Grbe Ntionl Reserch Council Ottw, Ontrio, Cnd ABSTRACT The Mchinery nd Engine Technology (MET) Progrm of the Ntionl Reserch Council of Cnd (NRCC) hs estblished progrm for the evlution of sensors to mesure gs turbine engine performnce ccurtely. The precise mesurement of fuel flow is n essentil prt of stedy-stte gs turbine performnce ssessment. Prompted by n interntionl engine testing nd informtion exchnge progrm, nd mndte to improve ll spects of gs turbine performnce evlution, the MET Lbortory hs criticlly exmined two types of fuel flowmeters, Coriolis nd turbine. The two flowmeter types re different in tht the Coriolis flowmeter mesures mss flow directly, while the turbine flowmeter mesures volumetric flow, which must be converted to mss flow for conventionl performnce nlysis. The direct mesurement of mss flow, using Coriolis flowmeter, hs mny dvntges in field testing of gs turbines, becuse it reduces the risk of errors resulting from the conversion process. Turbine flowmeters, on the other hnd, hve been regrded s n industry stndrd becuse they re compct, rugged, relible, nd reltively inexpensive. This pper describes the project objectives, the experimentl instlltion, nd the results of the comprison of the Coriolis nd turbine type flowmeters in stedy-stte performnce testing. Discussed re vritions between the two types of flowmeters due to fuel chrcteristics, fuel hndling equipment, coustic nd vibrtion interference nd instlltion effects. Also included in this pper re estimtions of mesurement uncertinties for both types of flowmeters. Results indicte tht the greement between Coriolis nd turbine type flowmeters is good over the entire stedy-stte operting rnge of typicl gs turbine engine. In some cses the repetbility of the Coriolis flowmeter is better thn the mnufcturers specifiction. Even significnt vrition in fuel density (1%), nd viscosity (3%), did not pper to compromise the bility of the Coriolis flowmeter to mtch the performnce of the turbine flowmeter. INTRODUCTION In the ccurte ssessment of gs turbine performnce, the estblishment of correct fuel flow is importnt. Fuel flow is considered s performnce prmeter on its own merits, but it lso ppers in the much used specific fuel consumption function. Thus the mesurement of fuel flow is criticl to the certifiction of new engines nd the cceptnce testing of overhuled ones. Lrgely prompted by the NRC's prticiption in the AGARDsponsored Uniform Engine Testing Progrm, n exmintion of the mesurement of fuel flow ws initited, with the purpose of improving ccurcy nd evluting new methods of flow estblishment. Although fuel flow, in vition gs turbine testing, is evluted in the form of mss flow, most mesurements re being crried out using volume flowmeters, predomintely of the turbine type (Grbe, 1988). Trditionlly, NRC hd been using turbine type flowmeters to mesure fuel flow volumetriclly, with pproprite conversion fctors to clculte mss flow. Recently, interest in the direct mesurement of mss flow, using Coriolis type flowmeters, hs emerged from field testing of gs turbines, in stedy-stte mode, where ccess to correct volume-mss conversion is not lwys vilble. The Coriolis type flowmeters hve been used for severl yers in the process industries to mesure nd control production of fluids nd fluid/solid mixtures. The emphsis in this role ws the necessity of simple, relible nd robust instrument to mesure flowrte independent of temperture, density, or viscosity. The use of Coriolis flowmeters to mesure fuel flowrte in gs turbine testing is reltively recent. The dvntges re obvious, direct mesurement of mss flow of fuel, simplicity, nd low mintennce. The disdvntges include possibly higher pressure losses (depending on internl tube configurtion) nd high initil costs (Furness, 1991). Presented t the Interntionl Gs Turbine nd Aeroengine Congress nd Exposition Cincinnti, Ohio My 24-27, 1993 This pper hs been ccepted for publiction in the Trnsctions of the ASME Discussion of it will be ccepted t ASME Hedqurters until September 3,1993 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
A limited comprison of the performnce of turbine flowmeters nd Coriolis type flowmeter ws undertken by NRC to get better understnding of both types of flow mesurement devices. All tests were confined to stedy-stte opertion. PROJECT OBJECTIVES The objectives of this flowmeter comprison project were: ) to ssess the strengths nd weknesses of both turbine nd Coriolis flowmeters, b) to evlute the Coriolis flowmeter s to its suitbility for use in gs turbine testing under stedy-stte lbortory conditions, c) to comment on the suitbility of the Coriolis flowmeter under field testing conditions, d) the verifiction of ccurcy clims of the Coriolis flowmeter, e) to exmine the clibrtion methodology for mss flowmeter. FUEL FLOW MEASUREMENT Before compring the performnce of turbine nd Coriolis type flowmeters, it is importnt to fully understnd the principles under which ech device opertes. The limittions nd strengths of ech flowmeter type obviously hve strong bering on the usefulness nd ccurcy of the test results obtinble in both lbortory nd field testing conditions. Included in this segment of this pper re brief descriptions of the operting principles of both types of flowmeters. Turbine Flowmeters The turbine flowmeter, s mesuring device for liquid nd gseous flow, hs been in use for considerble time, nd, hence, its principles re generlly well-known mong users. In brief, fluid flow is directed through metering body with finelymchined cylindricl duct, in which turbine rotor is plced, in line with the flow. Disregrding smll effects, the turbine rottes in direct proportion to the velocity of the fluid flow through the meter. A mgnetic or modulted crrier pickup detects the pssge of ech rotor blde tip nd genertes pulse. Becuse of geometric peculirities nd fluid effects, ech flowmeter must be clibrted for ccurte flow mesurement. This is done by correlting the pickup pulses with either known volumes of flow pssing by the turbine rotor or with known liquid mss flows pssing through the meter nd being collected nd weighed subsequently. An in-depth tretment of turbine flowmeter systems hs been given by Zimmermnn nd Decry (1977). Since the turbine flowmeter is volume flow mesuring pprtus, wheres fuel mss flows re rther needed in gs turbine testing, conversion from volume to mss is required. To do so, certin fluid properties must be estblished, nd their ccurcies re difectly reflected in the finl ccurcy of the mss flow. The eqution for fuel mss flow my tke the form: wf FREQ * 3.781673*RD Ti CT* K (1) Wf = observed fuel flow [lcg/s] FREQ = flowmeter frequency [pulses/s, Hertz] 3.781673 = volume-mss conversion fctor RDTf = reltive density (specific grvity) t fuel temperture CT = flowmeter therml correction fctor K = flowmeter clibrtion fctor [pulses/us gllon] A similr expression cn be written for flow units of lbm/h. Detils of the flow eqution derivtion cn be found in report by Grbe (1988). It should be noted tht the K-fctor hs the bsic form "pulses per unit volume"; the unit "US gllon" hs been crried over, in this instnce, from the originl one of the bllistic flow clibrtor, in use t the Ntionl Reserch Council in Ottw. To fcilitte dt comprison between different test nd fuel conditions, it is customry to reduce observed flow dt to stndrd vlues: NHC g, NHCR Wfcor = fuel flow corrected to stndrd conditions [kg/h or lb m/h] Wf = fuel flow t test conditions [kg/h or lb m/h] = (engine inlet totl pressure)/(stndrd dy brometric pressure) = (engine inlet totl temperture)/(stndrd dy temperture) NHC = net het of combustion [MJ/kg or BTU/lbm] NHCR = reference net het of combustion [MJ/kg or BTU/lb m] The first prt of the correction term yields fuel mss flow corrected to stndrd dy conditions, while the second prt llows for vrinces in energy content in certin fuel btch. In engine performnce estblishment, it is the energy input for given thrust or power output which, ultimtely, is of consequence. Coriolis Flowmeters A Coriolis mss flowmeter mesures mss flow directly, using the Coriolis Principle, which is bsed on the conservtion of ngulr momentum, s it pplies to the Coriolis ccelertion of given fluid. In principle, Coriolis mss flowmeter consists of tube with fixed inlet nd outlet, which is vibrted sinusoidlly from the xis formed by the inlet nd outlet ends. The tube my be either stright or omeg shped, nd is vibrted using drive coil ttched t the xis. Electromgnetic sensors re mounted upstrem nd downstrem of the drive coil to mesure velocity signls from the vibrting tube. This mens tht liquid flow is mesured by trnsferring vibrtionl energy from the meter tubing to the flowing liquid nd bck to the meter. To pprecite this principle, imgine vibrting tube s shown in Figure 1. If no liquid is flowing, the drive coil in the middle of the tube will cuse both rms to vibrte in phse. Mss flowing into the tube strts to receive vibrtionl energy from the tube wlls s it enters the first bend (Figure 2). In this process, the tube loses the sme mount of energy. The result is the phse of the vibrtionl cycle lgs t the upstrem sensor loction; the reverse will hppen t the downstrem loction. The liquid is vibrting s it enters the bend, but trnsfers this energy to the pipe. The result is tht the mss flow dvnces the vibrtionl phse t the downstrem sensor loction. When combined, these two chnges in vibrtionl phse produce twisting of the flow tube s shown in Figure 3. The (2) 2 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
mplitude of this twist is directly proportionl to the mss flow rte nd is nerly independent of the temperture, density, or viscosity of the liquid involved. In prcticl ppliction, Coriolis mss flowmeter my contin two prllel tubes, but the principle outlined' remins unchnged. LESS vi Figure 1. Coriolis Flowmeter Configurtion. UP STREAM SENSOR FLOW FLOW DOWN STREAM SENSOR MORE 4- Vi. Figure 2. Coriolis Flowmeter: Principles of Opertion. c- ------ FonE t FORCE COUPLE ) CCUPLE TOP VIEW Figure 3. Coriolis Flowmeter: Force Couple Genertion. TEST SET-UP AND INSTRUMENTATION To compre the turbine nd Coriolis flowmeters, the Coriolis meter ws instlled in series with two turbine meters in the fuel delivery system of gs turbine engine. The evlution procedures included observtions of the instlltion nd opertion of the meters in generl, nd more specificlly, comprison of the flow mesurements between the verge of two turbine meters, nd the Coriolis meter. Instlltion Criteri The test set-up ws designed to evlute the flowmeters under vrious conditions to estblish the effects of the following criteri: ) instlltion, b) fuel temperture, c) reltive density (specific grvity), d) viscosity, e) noise nd vibrtion, nd f) flow rnge. V) While most of the effects of the bove criteri on turbine meters re well documented (Grbe, 1988), the effects on the Coriolis meter re not. To estblish ny instlltion effects on the Coriolis meter, the meter ws instlled in severl configurtions: fixed mounting, nd flexible mounting. To nlyze fuel temperture effects, tests were performed on different dys with different inlet fuel tempertures. For the investigtion of reltive density nd viscosity effects, two fuel types were used, one 1% denser, nd with 3% higher viscosity thn the other. Noise nd vibrtion effects were investigted by plcing the Coriolis meter in close proximity to n fterburning turbofn engine producing noise levels up to 173 db. Finlly, the Coriolis meter ws tested over low nd high flow rnge using two different gs turbine engines. For low flow rnge testing (8-24 lbm/hr) n Allison T56 turboprop engine ws used, while for the high flow rnge (5-9 lbm/hr), the flowmeter ws mesuring the core flow of Generl Electric F44 fterburning turbofn engine. Instrumenttion Description The fuel flow mesurement system used for this study consisted of two turbine flowmeters, in series with one-hlf inch dimeter Coriolis mss flowmeter. For low flow rnge testing, two one-hlf inch dimeter turbine meters were used, while for high flow rnge testing, one three-qurter inch nd one inch turbine meter were instlled. Dt from the meters were recorded using NEFF 62 dt cquisition system controlled by DEC Microvx II computer. For ech instlltion, the gs turbine engine ws operted over its entire power rnge. At vrious power settings, five minute stbiliztion period ws observed before two three-minute stedystte dt scns were initited. Typiclly, up to six power settings (12 dt points) were recorded for ech test. A bllistic flow clibrtor ws used to ssess the ccurcy nd clibrtion of the turbine flowmeters. A brief description of the clibrtor nd its principle is included. Omnitrk Flow Clibrtor The Institute for Mechnicl Engineering, Ntionl Reserch Council, is the custodin of n Omnitrk bllistic flow clibrtor, Model OT-15, by Flow Technology, Inc. It clibrtes turbine flowmeter by correlting the pulses generted by its pick-off with precise volume of fluid. The Omnitrk bllistic clibrtor incorportes piston which trvels inside honed cylinder, pushing the clibrtion fluid long its pth, nd, further downstrem, through the flowmeter to be clibrted. A piston rod is connected to the piston, crrying photoelectric sensor. The sensor, or encoder, slides over finely etched glss rule, generting pulses from the etched mrkings. These pulses hve been, through previous clibrtion, correlted with specific volume, hence, precise clibrtion volume cn be determined from the encoder pulses. This correltion between encoder pulses nd volume forms the bsis of the clibrtion constnt of the clibrtor, lso referred to s the K-fctor of the clibrtor. As n indiction of the fine resolution of the clibrtor 3 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
clibrtion, some 62, mrkings on the glss rule represent one US gllon. A clibrtor K-fctor for the flowmeter is being clculted from primry dt through the reltionship: K - No FMP*T VOL T FMP* VOL K = clibrtion fctor of the flowmeter [pulses/us gllon] (or ny other specified unit volume) No. FMP = number of flowmeter pulses collected [pulses] T VOL = time required for the test volume to be displced [s] T FMP = time required for collecting the flowmeter pulses [s] VOL = volume of fluid displced [US gllon or frction thereof] (or ny other specified unit volume) A detiled description of the Omnitrk clibrtor cn be found in the mnufcturer's mnul (FTI 1982). Since the clibrtion fctor of the flowmeter is derived from the clibrtion constnt of the clibrtor, which is bsed on reference conditions, the K-fctor must be corrected to the ctul conditions, i.e. tempertures nd pressures, previling t the time of clibrtion (Grbe 1991). TEST RESULTS Before comprison between the turbine nd Coriolis flowmeters could be mde, it ws necessry to estblish the repetbility of the two turbine meters used s the reference for the low flow rnge nd high flow rnge testing. Previous work (McLeod nd Orbnski, 1992) determined tht the greement between the two one-hlf inch turbine flowmeters used with the Allison T56 engine ws ±.16%. For the higher flow rnge, the greement between the 3/4-inch nd 1-inch turbine flowmeters of the Generl Electric F44 testing ws ±.2%, s shown in Figure 4. (3) Low Flow Rnge Testing To evlute the Coriolis mss flowmeter in the lower flow regime, the device ws instlled in series with existing turbine meters in the fuel delivery system of n Allison T56 turboshft engine. The Coriolis mss flowmeter ws instlled in three different configurtions. In the first one, the flow sensor ws plced in the fuel line, hlf wy between the engine fuel control nd the fcility turbine meters. Two lengths of pproximtely two metres of flexible fuel line connected the Coriolis flow sensor to the engine nd the turbine meters upstrem. The flexible hoses were ttched directly to the flnges of the sensor unit. For the second set-up, the sensor ws moved to position one metre upstrem of the turbine meters. In both configurtions, the sensor ws plced on fom pd sitting on the concrete floor. For the finl configurtion, the Coriolis flow sensor ws rigidly bolted to the floor s described in the instlltion mnul (Schlumberger, 1991). A totl of 14 stedy-stte test runs were performed with the Coriolis mss flowmeter instlled in the fuel system. As shown in Figure 5, the comprison between the turbine nd Coriolis flowmeter is quite good, with 95% of the dt flling within the +.3% sctter bnd, over the tested flow rnge. The fuel temperture did not pper to hve ny influence on the test results s indicted in Figure 6. This includes testing done with two different fuel types. The first fuel hd reltive density of.763 nd viscosity of 1.194 centistokes t 15.56 C, while the second fuel hd reltive density of.839 nd viscosity of 4.112 centistokes. As fr s instlltion effects re concerned, there ws no pprent correltion between the three configurtions nd the vrition between the turbine nd Coriolis meters, s cn be seen from the plot ginst run numbers in Figure 7. Configurtion two ws n ttempt to see if the pressure fluctutions t the fuel control inlet were propgting upstrem nd ffecting the Coriolis sensor. This ws found not to be the cse. The sensor, plced less thn two metres from the engine did not experience ny fluctutions s result of noise, vibrtion, or electricl interference. Noise levels ner the sensor were pproximtely 125 dba.. o Oo d] EEO DO o m 8Q cso ob.2..3 e..5 1.2 1.1 1.6 1.8 2 ( Thousnd) FUEL FLOW ( TURBI NE 1)LBW HA Figure 4. Turbine Flowmeter Repetbility Figure 5. Low Flow Rnge Comprison 4 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
.6.5.1.4 3.2.1 -.2 -.3 -.4 % n 133 8 E] 3-4 g 3 cc I! 93 CIE co 8 CI,,p -. 9 -.5 -.6 -.2-8 -.9 _1.2 B c D o r.p -.5. _LIIII II 22 FUEL TEMPERATURE SEG. C (Thousnds) FUEL FLOW (TURBINE I) LBM/NR.6 5 4 3.2 -,2 -.3 -.5 Figure 6. Low Flow Rnge Temperture Effects g 192 8 8 B 194 196 191 2 RUN NUMBERS 6 8 B 22 24 Figure 7. Low Flow Rnge Instlltion Effects High Flow Rnge Testing To evlute the Coriolis mss flowmeter in the higher flow regime, the device ws plced in series with existing turbine meters in the fuel delivery system of Generl Electric F44 fterburning turbofn engine. The Coriolis mss flowmeter ws instlled in two different configurtions. In the first, the flow sensor ws plced in the fuel line, hlf wy between the engine fuel control nd the fcility turbine meters, sitting loosely on the floor. Approximtely two metres of flexible fuel line were between the engine nd the Coriolis flow sensor nd between the sensor nd the turbine meters upstrem. For the second set-up, the sensor ws rigidly bolted to the floor s described in the instlltion mnul (Schlumberger, 1991). Six stedy-stte test runs were performed with the Coriolis mss flowmeter instlled in the F44 fuel system. In Figure 8, the comprison between the turbine nd Coriolis flowmeter indictes divergence between the two fuel meter types of up to 1.2%, over the tested flow rnge. In every test, the Coriolis meter lwys red higher vlue thn the verge of the two turbine meters. Figure 8. High Flow Rnge Comprison To isolte the possible cuses of this divergence, the dt were nlyzed on run-to-run bsis. In Figure 9, the result show n interesting trend. Run numbers 92, 95, nd 96 were performed with the Coriolis meter sitting loosely on the floor, while runs 93, 94, nd 97 were crried out with the meter bolted solidly to the floor. For the loose mounting tests, the dt sctter is higher (.5 to.7%), thn for the solid mounting ones (.25 to.35 %). However, the solid mounting tests show significnt shift wy from the verged turbine meter vlues (up to 1.2%). It ws discovered tht the frequency output crd used in the Coriolis flowmeter receiver ws unstble, nd would drift between runs. After run 94 the frequency crd ws reclibrted, so tht runs 95 nd 96 strt closer to zero. After run 97, the crd ws reclibrted fter it ws noticed tht Coriolis meter redings were beginning to drift wy gin from the turbine meter redings. This frequency drifting is not relted to the Coriolis method of flow mesurement in ny wy; it is simply poor qulity frequency output crd for the meter chosen for this test progrm. If undetected nd uncorrected, the drifting cn led to significnt mesurement bis errors, nd, hence, steps must be tken to prevent this problem..1.2-3 - 4..5 -.6 -.9 8 92 94 8 RUN NUMBERS 96 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
Bsed on previous experience with Coriolis mss flowmeters (McLeod, 1987) the sensitivity of the Coriolis flow tubes to noise nd vibrtion is significnt. In the tests discussed here, the effects of loose versus solid mounting were mesurble. The divergence in the flowrte of the two meter types is speculted to be the result of irborne noise vibrting the Coriolis meter tubes. These vibrtions would cuse higher tube oscilltions, indicting higher flow rtes, s shown in Figure 8. In ddition, the devition between the two meter types increses with flowrte, since the coustic energy in the test cell lso is incresing with engine power. Unfortuntely, time constrints did not permit testing with n coustic enclosure surrounding the Coriolis meter to verify this hypothesis. Coriolis Meter Clibrtion Any flowmeter hs to be checked for its clibrtion, t the beginning of its service life nd periodiclly therefter. The clibrtion of turbine flowmeters is well-estblished nd documented. The clibrtion technique for mss flowmeters of the Coriolis type, with bllistic clibrtor, is less known, simply becuse these meters hve only recently come into wide-spred use. It hs been sid tht the ccurcy of Coriolis mss flowmeter is inherently superior to tht of bllistic clibrtor, nd, hence, clibrtion by tht pprtus would be meningless. However, until tht proposition hs been proven vlid, technique hs been developed t NRC by which mss flowmeters cn be clibrted. The mss flowmeter hs frequency output, in ddition to voltge one, which is proportionl to the flowrte. Thus, the meter cn be treted like turbine flowmeter in bllistic clibrtor, with the output prmeters being vlid entities, viz. volume flowrte nd K-fctor. The frequency, clculted in turbine flowmeter clibrtion, becomes now n input prmeter. To obtin mss flow clibrtion, however, some further steps re required. A mss flow hs to be computed by the eqution: th - V x RD x 3.781673 [kg/mill] (4) m dot = mss flow t the fluid temperture [kg/min] V dot = volume flow rte through the meter [US gllon/min] RD = reltive density of clibrtion fluid t fluid temperture 3.781673 = volume-mss conversion [kg H 2O @15.56 C/US gllon] Knowing the mss flowrte of clibrtion point, one cn clculte modified K-fctor for the meter in terms of "pulses per kg", insted of "pulses per US gllon" by: Km FREQ x 6 - [pulses/kg] (5) The question remins how to evlute best the clibrtion. Two possibilities hve been exmined. One, the most logicl one, hs the mss flow plotted ginst frequency, on the bsis tht direct proportionlity supposedly exists between them. The other hs the modified K-fctor, K., plotted ginst frequency. Since viscosity is sid not to ffect the flow mesurement of Coriolis meter, frequency does not hve to be corrected for its effects. Exmintion of the two pproches shows tht the ltter one is superior in tht it produces fr better resolution, nd, hence, more ccurte clibrtion evlution. As n exmple, in one prticulr mss flowmeter clibrtion it ws found tht differences, between distinct clibrtion points nd vlues obtined from curves, vried from.1% to 1.2% for the K o, pproch nd.1% to 4.5% for the stright mss flow one. The differences incresed from high to low flows. This observtion leds to the conclusion tht, on ccount of the better resolution of its plotting scle, the clibrtion evlution vi the modified K-fctor yields more ccurte results nd should be preferred. UNCERTAINTY ANALYSIS Flow Mesurement by Turbine Flowmeter The uncertinty nlysis of fuel flow mesurement is rther complex nd depends on mny smll contributors. An ttempt hs been mde by Grbe (1988) to give detiled error nlysis of the whole fuel flow mesuring system, which uses turbine flowmeter. It ws shown tht the possible error depends, to lrge degree, on the conditions under which the mesurements re tken. In tht nlysis, two conditions were chosen: one severe the other verge. The severe condition, for exmple, would consider extreme fluid tempertures, low flow rtes, which mens low meter frequency, nd method of reltive density determintion with high reproducibility uncertinty. The verge conditions were those more likely to be encountered in the field. The contributing elements of n uncertinty nlysis of observed fuel flow include such items s the turbine flowmeter frequency, the fluid reltive density, the correction for flowmeter therml expnsion, nd the K-fctor, see eqution 1. For the corrected fuel flow, inlet tempertures nd pressures, s well s the fuel net het of combustion, further dd to the finl uncertinty. Ech of these items depend, in turn, on contributing elements of their own. For exmple, reltive density, formerly clled specific grvity, t mesurement temperture, is function of its reltive density t reference temperture, the fuel temperture, nd the fuel's criticl temperture. The uncertinty of ech of these contributors is creted during mesurement. Tking ll of these possible error contributions into ccount, it ws found tht, in well-run system, where gret cre is tken t ll steps in the chin, the following uncertinties my occur. The observed fuel flow, under verge mesurement conditions, could be expected to hve n overll uncertinty of ±.4%. Under severe conditions, this uncertinty would nerly double to +.7%. For corrected fuel flow, including corrections for the fuel net het of combustion, the uncertinty would be +.65% for verge conditions nd +1.% for severe ones. It must be borne in mind tht these uncertinties re by no mens gurnteed. Only if creful steps re tken long the fuel flow estblishment pth, cn these rther tight uncertinties be chieved. Ech element contributes, in some wy, to the finl ccurcy of the fuel flow estblishment. For exmple, if n verge K-fctor were used for the whole flow rnge, insted of following the universl curve for ccurte locl vlues, the K-fctor error contribution could mount to.5%, rther thn predicted.2% from the nlysis (Grbe 1988). 6 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use
Flow Mesurement by Coriolis Flowmeter The contributing elements of n uncertinty nlysis of observed fuel flow for Coriolis flowmeter include such items s the drive coil frequency, the frequency response of the electromgnetic sensors, the therml correction for flowmeter tube elsticity chnges, zero stbility, nd the K-fctor. For the corrected fuel flow, inlet tempertures nd pressures, nd the fuel net het of combustion, must be considered to determine the finl uncertinty. Ech of these items depend, in turn, on contributing elements of their own. Tking ll of these possible error contributions into ccount, it ws found tht the following uncertinties my occur. The observed fuel flow, under verge mesurement conditions, could be expected to hve n uncertinty of +.15% of reding ± zero stbility. The zero stbility cn be s high s +.5% of reding bsed on the test results shown here nd in previously published work (Keit, 1989). SUMMARY AND CONCLUSIONS For ccurte fuel flow mesurement, certin precutions must be tken in instlling nd operting flowmeter, be it turbine or Coriolis type device. The turbine flowmeter is reltively simple device mesuring volumetric flowrte, which is ffected by fuel temperture, reltive density, nd viscosity of the fluid. The Coriolis mss flowmeter indictes mss flow directly through resonbly complex procedure, with little or no influence from the properties of the fluid. Comprison tests between the turbine nd Coriolis flowmeters indicted good greement of bout +.3% over the lower portion of the flow rnge of the Coriolis meter exmined. At higher flowrtes, the Coriolis flowmeter indicted flowrtes pproximtely.5% higher thn the two turbine meter in series with it. This divergence ws ttributed to noise nd vibrtion emnting from the gs turbine. Fuel temperture, reltive density or viscosity did not pper to influence the Coriolis flowmeter in ny wy. Instlltion effects on the Coriolis flowmeter were miniml, nd the pressure losses were similr to tht for the turbine flowmeters (depending on turbine meter dimeter). Drifting in the electronic components of the Coriolis flowmeter required frequent djustments of the frequency bord to mintin close greement with turbine flowmeter results. If undetected nd uncorrected, these drifts could led to substntil mesurement errors. REFERENCES FTI, 1982, "Instlltion, Opertion nd Mintennce Mnul Omnitrk," Flow Technology, Inc., 425 Est Brodwy Rod, Phoenix, AZ, 854. Furness, R.A. 1991, "BS745: The Principles of Flowmeter Selection," Flow Mesurement nd Instrumenttion, Vol.2, October 1991, pg 233-242. Grbe, W. 1988, "Fuel Flow Mesurement in Gs Turbine Testing," Division of Mechnicl Engineering, Ntionl Reserch Council, Ottw, Ontrio, TR-ENG-1 (NRC No. 2988). Grbe, W. 1991, "Turbine Flowmeter Clibrtion," Institute for Mechnicl Engineering, Ntionl Reserch Council, Ottw, Ontrio, CAT-ENG-13. Keit, N.M., 1989, "Contribution to the Understnding of the Zero Shift Effects in Coriolis Mss Flowmeters," Flow Mesurement nd Instrumenttion, Vol.1, October 1989, pg 39-43. McLeod, J.D., 1987, "Evlution of the EXAC Mss Flowmeter," Division of Mechnicl Engineering, Ntionl Reserch Council, Ottw, Ontrio, CAT-ENG-2. McLeod, J.D., B. Orbnski, 1992, "Turbine Rebuild Effects on Gs Turbine Performnce," ASME 92-GT-23. Pik, J.S., K.W. Lim, K.B. Lee, 199, "Clibrtion of Coriolis Mss Flowmeters using Dynmic Weighing Method," Flow Mesurement nd Instrumenttion, Vol.1, April 199, pg 171-175. Schlumberger Industries Inc., 1991, "M-dot Direct Mss Flowmeter with Dtmte 2 Operting nd Mintennce Mnul." Zimmermn, R., D. Deery, 1977, "Hndbook for Turbine Flowmeter Systems," Flow Technology Inc., 425 Est Brodwy Rod, Phoenix, AZ, 854. RECOMMENDATIONS Bsed on previous experience with Coriolis mss flowmeters (McLeod, 1987) nd the results of this study, the Coriolis flowmeter hs shown to hve the cpbility of mesuring ccurtely fuel flow to gs turbine, provided certin precutions re observed. It is recommended tht Coriolis flowmeter be seriously considered for gs turbine testing, both in the lbortory nd in field instlltions. However, becuse of the complexity of the electronic conditioning required to monitor the Coriolis flowmeter, the device should, for the time being, be used in series with turbine flowmeter to detect ny possible drift in the Coriolis meter redings. 7 Downloded From: https://proceedings.smedigitlcollection.sme.org/ on 8/27/218 Terms of Use: http://www.sme.org/bout-sme/terms-of-use