THE GAS TINY FLOW MEASUREMENT INSTRUMENTATION

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1 HE GAS INY FLOW MEASUEMEN INSUMENAION Milan Adámek, Per Neumann, Marin Pospíšilík omas Baa Universiy in Zlín Deparmen of Securiy Engineeriny, Faculy of Applied Informaics Nad Sráněmi 511, 76005, Zlín Czech epublic KEYWODS flow measuremen, calorimeric sensor, ime of fligh, heaing power, mass and hea ransfer, modelling, Femlab, flow ube, flow range ABSAC he paper presens he design and experimenal experience wih he gas flow measuremen insrumen for he range of (5 5) ml/hr. he aimed applicaion area is in a biochemical laboraory for he sudy of reacion kineic of sedimens decomposiion in wase waer. he ime of fligh ype of sensor wih one upsream and one downsream emperaure sensor has been chosen for he sudy. We explain he basic operaion principles of he iny flow measuremen and he sensor srucure. In he numerical model paragraph, we are describing he basic configuraion model and he modelling resuls. As he hree dimensional simulaion would be very ime consuming process, we have simplified he simulaion for only wo dimensional ask. he presened diagrams are derived for differen gases (, nirogen, carbon oxide and chlorine) and sensor ube maerials, namely seel, copper, and plexi-glass. We presen also he experimenal se up including he design and sensor parameers. he paragraph wih experimenal resuls and discussion on hem illusraes he good correspondence wih expeced values. he paper concludes wih he employmen of designed gas flowmeer in he biochemical laboraory. INODUCION he accurae measuremen and conrol of iny liquid flows in he amoun of nanoliers up o milliliers per minue is becoming more and more imporan for a lo of applicaions in he life science. In some applicaions, such as process conrol in precise semiconducor manufacuring, chemical and pharmaceuical indusries and biochemical engineering, miniaurized liquid flow sensors are more and more encounered. Mos of hem operae on he mehod of hermal ranspor and are fabricaed from a silicon crysal by using micromachining echnology. he hermal devices for flow measuremen may be grouped in wo differen classes. he firs class groups hermal mass flowmeers ha are measuring he effec of he flowing fluid on a ho body (he increase of heaing power wih consan heaer emperaure, he decrease of heaer emperaure wih consan heaing power). hey are usually called ho wire, ho film sensors or ho elemen sensors. he resisive elemen is used boh as heaer and as sensor simulaneously. he emperaure can be obained from is elecrical resisance. he second class group hermal mass flowmeers ha measure he displacemen of emperaure profile around he heaer which is modulaed by he fluid flow. hese sensors are called calorimeric sensors. he special ype of hermal mass flowmeers in he class menioned above is hermal mass flowmeer ha measure he hea pulse passage ime over a known disance. hey are usually called ime of fligh sensors [1]. Many of he microflow sensors use a hermopile as a emperaure sensor; however, he hermoelecric coefficien of he sandard elemens used in he inegraed circui is smaller han ha of convenional hermocouples. hus, a resuling oupu signal may be very small which requires amplifiers inegraed direcly ino he sensor []. Up o now, very few of nowadays commercially offered flow sensors are equipped wih he feaures menioned above. One of possible mehod of liquid flow measuring is presened in his paper. he properies of a ime of fligh sensor are sudied. he FEMLAB program was used for he sudy of flow sensor properies. SENSO SUCUE AND BASIC OPEAING PINCIPLE he flow sensor consiss of a heaer and one or more downsream emperaure sensors, as shown in he Figure 1a. he heaer is acivaed by curren pulses. he ranspor of he generaed hea is a combinaion of diffusion and forced convecion. he resuling emperaure field can be deeced by emperaure sensors locaed downsream. he deeced emperaure oupu signal of he emperaure sensor is a funcion of ime and flow velociy. he sensor oupu is he ime difference beween he saring poin of he generaed hea pulse and he poin in ime a which a maximum emperaure a he downsream sensor is reached, Figure 1b. his ype of sensor has he same consrains as he inrusive ype of calorimeric sensors: corrosion, Proceedings 9h European Conference on Modelling and Simulaion ECMS Valeri M. Mladenov, Peia Georgieva, Grisha Spasov, Galidiya Perova (Ediors) ISBN: / ISBN: (CD)

2 erosion and leakage [3]. Since he signal processing needs some ime o measure he ime difference, his sensor ype is no suiable for dynamic measuremen. On he oher side, he advanage of his ype of flow sensor is he independence on he fluid emperaure in he wider flow range. he influence of fluid properies on he mass flow sensor oupu is described in []. emperaure. hey all are inerrelaed hrough bidirecional muliphysics couplings. he equaions are: Conservaion of mass: coninuiy equaion ρ + ( ρu) = 0 (3) Flow Heaer Q emperaure sensor emperaure Hea pulse MAX v>0 v=0 o ime difference o l/v Conservaion of momenum: Navier Sokes equaion ρ u + ρ = + η + (u. )u p u F () ime difference Average velociy v Conservaion of energy: energy equaion a) b) c) Figure 1: ime of fligh sensor: a) principle; b) emperaure a he downsream sensor; c) sensor characerisic he ranspor of he hea generaed in a line source hrough a fluid follows he energy equaion [5] q u ρc ρc λ + = + (1) where is he emperaure, c is he specific hea a he consan pressure, ρ is he densiy, λ is he hermal conduciviy, q is he amoun of hea per uni of volume and ime. he analyical soluion of his differenial equaion for a pulse signal wih inpu srengh q (Wm -1 ) is given in [5] as ( x u) q ( x, y, ) = exp πλ a where a denoes he hermal diffusiviy. () NUMEICAL MODEL In he presened work, he properies of he ime of fligh sensor were invesigaed using commercially available program FEMLAB. Femlab is an ineracive environmen for modelling and solving problems based on parial differenial equaions. his program applies he finie elemen mehod (FEM) for he PDEs sysem solving [6]. he simulaed ime of fligh sensor is a muliphysics model which means ha i involves more han one kind of physics. In his case, here are Navier- Sokes equaions from fluid dynamics ogeher wih a hea ransfer equaion ha is essenially a conveciondiffusion equaion. here are hree unknown field variables: he velociy u, he pressure p and he λ q ρc ρc + ν = + where η is he dynamic viscosiy. BASIC CONFIGUAION (5) Since a ypical full hree dimensional simulaion of he sensor requires in excess of 10 5 cells and herefore several compuaional days, i was decided o invesigae several configuraions in wo dimensions a firs. Maerials: seel, cooper aluminium, plasic Specific gas Heaing elemen H emperaure sensor Figure : Basic configuraion sudied U H D U D Flow inle Flow oule he wo dimensional configuraion assumed in he presened work is illusraed in Figure. Boundary layer Heaing elemen Consrucive maerial Sensor ube Figure 3: Parial view of he compuaional grid for he basic configuraion

3 A srucured compuaional grid consising of more han 3000 cells was generaed. ose aenion was paid o he grid resoluion in criical areas such as boundary layers and he surroundings of he heaer. A par of he grid for he basic configuraion is displayed in Figure 3. Even in he wo dimensional case, he convergence o a correc soluion required several compuaional hours on a, GHz PC. he properies of he ime of fligh sensor were invesigaed a he relaively very low flow raes. In able 1, here are some inle gas velociies v used in he sensor model and he corresponding flow rae Q (he inner diameer of sensor ube is 1 mm). able 1. Inle speeds of fluen gas. v(mm s-1) Q(ml h-1) 1,76 5 3,5 10 5,9 15 7,08 0 8,8 5 he effecs of he sensor oupu ube consrucive maerial were invesigaed a he same ime, oo. he boundary condiions of he sensor model and he hea coefficiens can be found in Figure. he ranspor of he hea from he sensor ube o he ambien is expressed as: 1 (6) h = 1 δ α1 k α where h is he hea ransfer coefficien, α 1 is he coefficien of hea ransfer by convecion (from sensor ube o consrucive maerial), k is he hermal conduciviy of he consrucive maerial, α is he coefficien of hea ransfer by convecion (from consrucive maerial o ambien) and δ is he hickness of he consrucive maerial. he coefficien of hea ransfer by convecion from sensor ube o consrucive maerial α 1 was derived (forced convecion) wih he help of Nussel number expressed as [7]: d η Nu 1,86( Pe ) ( ) 1 = l 3 0,1 (7) ηw where Pe is Pecle number, η is dynamic viscosiy, η W is dynamic viscosiy a wall emperaure, l is lengh of hea ransfer surface and d is inner diameer of he hea exchanger shell. he coefficien of hea ransfer by convecion from consrucive maerial o ambien α was calculaed (naural convecion) wih he help of Nussel number expressed as [7]: y x Maerials: Seel, cooper, plasic glass Velociy: V X=V Y=0 Maerial: Specific gas Velociy: V=0; X V=0 Y Consan emperaure Forced convecion α 1 λ α Heaing elemen Hea ransmission emperaure sensor Naural convecion Gas inle Consan Pressure Gas oule Consan Pressure Hea flux q=0 Figure : Boundary seings in he model of he ime of fligh sensor he properies of he ime of fligh sensor were simulaed and verified for differen consrucive maerials and differen flowing gases, able and able 3. able. Physical consans of he applied gases. Flowing gases Densiy ρ (kg.m -3 ) Hea capaciy c (J.kg -1.K -1 ) hermal conduciviy λ (W.m -1.K -1 ) Dynamic viscosiy η (Pa.s) 1, , , N 1, ,055 18, , ,008 13, , ,05 18, able 3. Physical consans of he applied consrucive maerials. Consrucive Densiy Hea hermal maerials ρ (kg.m -3 capaciy conduciviy ) c (J.kg -1.K -1 ) k (W.m -1.K -1 ) copper seel plexi-glass ,18 MODELLING ESULS he funcionaliy Δ (Figure 1) on he flow rae Q a downsream sensor D are shown in Figure 5, 6, 7; he emperaure MAX was measured in he disance of 1,5mm from he heaer (in he middle of emperaure sensor) in he models. he menioned emperaure funcionaliies a he upsream sensor U are depiced in Figure 8, 9, 10. Figure 11 shows he funcionaliy of ime difference Δ on he flow velociy u. As can be seen in Figure 1, Δ is he difference beween he ime of he hea pulse and he ime of MAX. Nu 1/8 = 1,18.( Gr. Pr) (8) where Gr is Grashof number and Pr is Prandl number.

4 N N Figure 5: he funcionaliy Δ on flow rae Q a downsream sensor D, consrucive maerial plexi glass Figure 9: he funcionaliy Δ on flow rae Q a upsream sensor U, consrucive maerial seel N N Figure 10: he funcionaliy Δ on flow rae Q a upsream sensor U, consrucive maerial cooper Figure 6: he funcionaliy Δ on flow rae Q a downsream sensor, consrucive maerial seel 1,5 1,0 N 0,5 N Figure 7: he funcionaliy Δ on flow rae Q a downsream sensor D, consrucive maerial cooper Figure 8: he funcionaliy Δ on flow rae Q a upsream sensor U, consrucive maerial plexi glass N Figure 11: he funcionaliy Δ on flow rae Q a upsream and downsream sensor, consrucive maerial cooper EXPEIMENAL SE UP he main goal of his work was o develop he flowmeer wih he measured flow range of (5 5) ml/hr. However, he mechanical and elecrical design was imporan as weel because of pracical realisaion. FLOW UBE he modelling resuls had se he inspiraion daa for a consrucion varian of he flow ube. Several gas flow sensors have been buil, wih flow ubes made ou of sainless seel and cooper, and wih inernal diameers varying beween 0,5 and 1,5 mm. he corresponding inernal volumes of he flow sensor ubes are 9,8 μl and 39,3 μl, respecively.

5 75 60 Figure 1: he flow ube 50 mm SENSO ELEMEN here was used he produc of Swiss company Flow Sens, FS as sensor elemen. he FS is he resul of coninuous developmen of IS AG qualiy producs. his new elemen consiss of hree emperaure depending plainum resisors, all deposied on one subsrae. he low-ohm resisor wih a small area is used as a heaer, whereas he wo high-ohm resisors on he righ and on he lef side are for measuring he mass flow and he direcion. As a resul of he lile hermal mass, his flow sensor has fas heaing and cooling response imes. echnical specificaions of he menioned sensor are [8]: esponse ime: < 0.5 s emperaure range: C emperaure sensiiviy: < 0.1 %/K Permissible pressure: 100 bar (depending on he sensors incorporaion, higher pressure upon requess) Permissible humidiy: % rh (no condensaion) Elecrical connecion flexible circui, compaible wih ZIF connecor Heaer: H (0 C) = 5 Ω Measuring elemens: L, (0 C) = 50 Ω Sensor dimensions: 5 x 3.5 x 0.15 mm Subsrae maerial: ceramic 0.15mm ,10 0,0 0,30 0,0 0,50 Figure 15: Dynamic characerisic of sensor elemen ELECONIC CICUI he mass flow conroller implemenaion was buil of wo sensors working according o he ime of fligh measuremen principle. Boh emperaure sensors need heir own specific elecronic circuiry which is based upon a Wheasone bridge configuraion. he elecronic circuiry convers he oupu signals, namely Δ of each emperaure sensor ino an oupu volage. he iems o be specified in Figure 16 are: U IH supply volage of heaer U CC supply volage of Wheasone bridge U OL oupu volage of upsream emperaure sensor U O oupu sensor of downsream emperaure sensor 3 1 L H 1 3 U IH U OL U O U CC GND L H Figure 13: Sensor elemen ZIF connecor Figure 16: Elecronic circuiry he heaer is acivaed periodically; he pulse heaing is used in flow ube according o he ime of fligh measuremen principle. A lengh of he heaing pulses is 0, s, a period of heaing pulses is 3 s emperaure elemen L emperaure elemen Figure 1: Saic characerisic of sensor elemen ESULS AND DISCUSSION he oupu signal of he flow sensors was measured for flow ranges varying beween 5 5 ml/hr in he downsream and upsream sensor. he mass flow conroller was used for measuremens of he dynamic behaviour. he following wo variaions in se poin were sepwise performed: 0% 100% 0% 0% 0% 60% 80% 100% he resuling response of he mass flow sensor was measured wih a digial oscilloscope.

6 Figure 17: Measuremen resuls obained wih gas flow sensor (downsream sensor) wih flow range 5 ml/h 100 % according o he ime of fligh measuremen principle and is working range; he flow ube is made of sainless seel and have an inernal diameer of 1 mm Figure 18: Measuremen resuls obained wih gas flow sensor (upsream sensor) wih flow range 5 ml/h 100 % according o he ime of fligh measuremen principle and is working range; he flow ube is made of sainless seel and have an inernal diameer of 1 mm. he measured curves, as displayed in Figures 17 hrough 19, correspond well wih he heoreically expeced values as calculaed wih equaions (3), () and (5). However, some deviaions beween heory and measuremens have occurred. hey can be explained as follows: real dimensions, real emperaures and pressures differed from he values used in he calculaions. no all boundary condiions for equaions (3), () and (5) were fully fulfilled, so ha he hea ransfer had a somewha differen behaviour han expeced. he measured response imes, as shown in Figure 19, are all wihin he value of 98% = 6 s. he above menioned flow sensor srucures and operaing principles have he following innovaive feaures and advanages: he flow sensor comprises a shor sraigh flow ube, wih an inernal diameer varying beween 0,5 and 1,5 mm, hus having a small inernal volume, varying beween 9,8 μl and 39,3 μl. he measurable flow range is 5 o 5 ml/h, he response ime 98% is 6 second. he measurable flow range can easily be adjused by varying he inernal diameer, maerial and wall hickness of he flow ube. he maerial of he flow ube can be eiher sainless seel or cooper or plasic glass; oher maerials may also prove o be feasible. he lengh of he flow sensor ube is he same for all flow ranges. his enables a modular se-up and exchangeabiliy of insrumens. 100% Compuer 0% Q(ml/h) Gas Flowmeer (ime - of - Fligh Sensor) hree Way Valve N 100% HO Bioreacor hermosa 0% Sedimen Figure 19: Measured response imes of a gas flow sensor adjused for : 5 ml/h 5 V; he X - axis represens he ime [s] wih s / div., he Y - axis displays he oupu volage [V] wih 1 V / div.; he flow ube is made of sainless seel and has an inernal diameer of 1 mm; he sensor is working according o he ime of fligh measuremen principle. Sirrer magneic Figure 0: Employmen of designed flowmeer in a biochemical laboraory CONCLUSIONS In his aricle, he measuremen mehod of small gas flow called as ime of fligh mehod is presened. he measuremen resuls exhibi ha he designed flow

7 sensor is accepable for slow processes wih reference o response ime of 98% = 6 s. he designed flowmeer has been used in a biochemical laboraory for sudy of reacion kineic of sedimens decomposiion in he wase waer; he decomposiion akes abou 36 hours. A basic se-up is illusraed in Figure 0 which demonsraes he employmen of designed flowmeer in a biochemical laboraory. EFEENCES Webser, J.: he measuremen, insrumenaion and sensors, Springer, Fraden, J.: Handbook of modern sensors, Springer, 00. Lammerink,., Dijksra,F., Z. Housek and J. Kuijk,: Inelligen gas/mixure flow sensor, J Sensors and Acuaors, Volume A 37/38, p. 5-50, Bonne, U.: Fully compensaed flow microsensor for elecronic gas meering, In Proc. In. Gas esearch Conf. 859, 199. Kuijk, J., Lammerink,., Bree, H., Elwenspoek, M., and Fluiman, L.: Muliparameer deecion in fluid flow, J Sensors and Acuaors, Volume A 6/7, p. 380-, Perry,. and Chilon, C.: Chemical engineers handbook, McGran Hill, he elecronic componen auheniciy analysis and failure diagnosis. His address is: neumann@fai.ub.cz MAIN POSPÍŠILÍK graduaed in 008 from Czech echnical Universiy in Prague, Czech epublic, in Microelecronics. Having received his Ph.D. degree in Engineering Informaics a omas Baa Universiy in 013, he became an assisan and researcher a he Deparmen of Compuer and Communicaion Sysems of Faculy of Applied Informaics of he omas Baa Universiy in Zlín, Czech epublic. His curren research covers he following opics: elecromagneic compaibiliy, shielding effeciveness of maerials for avionics, design of consrucion of elecrical circuis and esing of elecrical devices considering he securiy of communicaion. he securiy issues are invesigaed in cooperaion wih Escola Superior de ecnologia e Gesão, Beja, Porugal. His address is: pospisilik@fai.ub.cz. AUHO BIOGAPHIES MILAN ADÁMEK graduaed in 1990 from he Olomouc Palacky Universiy, Czech epublic. He received his Ph.D. degree in echnical Cyberneics a omas Baa Universiy in Zlin in 00. From 1997 o 008 he worked as senior lecurer a he Faculy of echnology, Brno Universiy of echnology. From 008 he has been working as an associae professor a he Deparmen of Elecronic and Measuremen, Faculy of Applied Informaics of he omas Baa Universiy in Zlín, Czech epublic. Curren work covers following areas: power lines, camera sysem, sensors. His address is: adamek@fai.ub.cz. Per NEUMANN has been graduaed from he Brno echnical Universiy in Elecronic echnology in 197. He has acquired he indusrial experience in he field of medical elecronics and qualiy managemen as &D engineer. He received his Ph.D. degree in echnical Cyberneics a omas Baa Universiy in Zlin in 001. He has been lecuring and working in he universiy research area since 199. He was engaged in he SM echnology raining, equipmen insallaion and servicing more han 10 years beween 1997 and 009. He is currenly working as a senior lecurer a omas Baa Universiy in Zlin. His research work is aimed a