INVESTIGATION OF UPSTREAM LENGTH REQUIREMENTS FOR VENTURI TUBE INSTALLATION USING CFD 1 A.Tukimin, 2 M.Zuber, 2 K.A.Ahmad, 2 S.

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1 Sci.Int.(Lahor),9(5),5-,07 ISSN 0-56;CODEN: SINTE 8 5 INVESTIGATION OF UPSTREAM LENGTH REQUIREMENTS FOR VENTURI TUBE INSTALLATION USING CFD A.Tukimin, M.Zubr, K.A.Ahmad, S.Saadon Dpartmnt of Mchanical and Manufacturing Enginring, Faculty of Enginring, Univrsiti Putra Malaysia, Jalan Upm, 00 Srdang, Slangor, Malaysia Dpartmnt of Arospac Enginring, Faculty of Enginring, Univrsiti Putra Malaysia, Jalan Upm, 00 Srdang, Slangor, Malaysia For Corrspondnc; aguinni@gmail.com, *mdzubairmanipal@gmail.com ABSTRACT: Th inallation of Vnturi tubs for high accuracy flow masurmnt in indurial application is normally basd on th availabl intrnational andards and guidlins. Th intrnational andard ISO 567- provids guidlins on th inallation rquirmnts for Vnturi in trms of rquirmnts and configurations. This guidlin indicats that any inallation with lssr than th givn minimum valu, will incur additional 0.5% uncrtainty on th discha coffic of th Vnturi tub. Th approach indicatd by th intrnational andard is vry gnral and consrvativ. In this work, th numrical simulation was usd to invigat th impact on th discha coffic, Cd, for inallation with lssr than th givn minimum valu by comparing th numrical simulation rsults and ntal data, for Vnturi tubs ranging from 00 mm to 50 mm. It was found that th numrical simulation rsults wr within +/- 0.5% uncrtainty and this is in lin with th guidlins by th intrnational andard.. INTRODUCTION As th diffrntial prssur typ flow mtr, such as Vnturi and orific plat, bcoms mor applicabl in th accurat flow mtring applications, th undranding on its prformanc in various inallation configurations is bcoming critical in ordr to nsur th ovrall masurmnt accuracy rquirmnt is mt. Earlir works of Himp t al. on th influnc of upram bnds on th discha coffics, Cd, of classical Vnturi tubs and orific plats indicatd that th for pip bnds upram of an orific with undiurbd inlt sctions smallr, as dmandd in ISO 567-, it was rcommndd to inall th prssur taps in th dirction of th innr sid of th bnd (0 o angl position) []. Anothr works by Radr-Harris t al. focusd on ntal works in th allowabl ps in pipwork upram of orific plats. Th rsults of th works indicatd that if th vry fir fitting is placd 0D (D is th intrnal pip diamtr) upram of th orific plat, th xiing ncssitis of 0.% of D ar unduly rrictiv and that xpansion ps of up to % of D and contraction ps up to 6% of D can b prmittd []. In 00, Intrnational Standardization Organization (ISO) committ producd th rvision 00 of th ISO 567 intrnational andard which covrs th guidlins on upram raight rquirmnt for diffrntial prssur dvics, such as Vnturi tubs and orific plats. This papr prsnts th work on using Computational Fluid Dynamics (CFD) to invigat th impact of upram raight lngth on th masurmnt accuracy of Vnturi tubs, in accordanc to ISO 567- [].. SCOPE OF THE WORK Vnturi tubs Th work uss th Vnturi tub with sizs ranging from 00 mm to 50 mm of intrnal pip diamtr. Th Vnturi tubs prssur rating is ASME 900 lbs, with convnt angl and 5 divnt angl of th inlt and outlt cons, rspctivly. Upram raight lngth Th numrical simulation focuss on 0D and D upram raight lngth inallation configurations. According to ISO 567-, 0D is th minimal rquirmnt for zro additional uncrtainty on discha coffic. Th D is slctd as ISO 567- indicats any btwn 0D and D givs 0.5% additional uncrtainty to th discha coffic, and this is th short upram raight lngth indicatd by th guidlin which provids usabl additional uncrtainty valu to b usd in th masurmnt.. METHODS Th work involvd stting up th modls in th ANSYS DsignModllr, similar to th physical Vnturi tubs usd in th ntal calibration. Th numrical simulation was prformd on ths modls. Th outputs of th numrical simulation, which ar th vlocitis and diffrntial prssurs, wr thn usd to calculat th discha coffic of th Vnturi tubs. Th discha coffic, Cd, was calculatd using Eq. (): Cd = m(-β ) 0.5 / (πεd ) / (00000Dp ρ ) 0.5 () Whr m is th rfrnc gas mass flow rat (kg/s), β is th diamtr ratio (-), ε is th gas xpansibility (-), d is th intrnal throat diamtr (m), ρ is th upram gas dnsity (kg/m ) and Dp is th masur of upram-to-throat diffrntial prssur (bar) []. Exprimntal calibration Th National Enginring Laboratory (NEL) in th Unitd Kingdom was usd to prform th ntal calibration of th Vnturi tubs. Th ntal stup was basd on 0D pip spool, which is way byond th minimum zro additional uncrtainty upram raight lngth as indicatd by ISO Th nitrogn gas was usd as th calibration gas, with varying flow rats and vlocitis applid during th t. Th collctd calibration data was usd as th baslin rfrnc whn comparing th discha coffic btwn nt and numrical simulation. Tabl,, and provid th ovrviw of th t matrix for ach siz of th Vnturi tubs.

6 ISSN 0-56;CODEN: SINTE 8 Sci.Int.(Lahor),9(5),5-,07 Poi nt Tabl : matrix for 00 mm Vnturi tub u r mpra tur Flowrat Nitrog n dnsity (-) (bar) ( C) (m /h) kg/m m/s suprfic ial vlocity.60 7.95 98 9.78.

2 6 ISSN 0-56;CODEN: SINTE 8 Sci.Int.(Lahor),9(5),5-,07 Poi nt Tabl : matrix for 00 mm Vnturi tub u r mpra tur Flowrat Nitrog n dnsity (-) (bar) ( C) (m /h) kg/m m/s suprfic ial vlocity Poi nt Tabl : matrix for 50 mm Vnturi tub u r mpra tur Flowrat Nitrog n dnsity (-) (bar) ( C) (m /h) kg/m m/s suprfici al vlocity Th -dimnsional symmtry had bn usd for th analysis of th simulation outputs. ur basd solvr and SIMPLE prssur-vlocity coupling had bn usd as ths ar applicabl for wid rang of flow rgims. All th cass in th simulation wr basd on th turbulnt flow rgim, as all th t points in th physical nt calibration wr in th turbulnt flow rgim. Th Standard K-Epsilon (SKE) turbulnc modl had bn usd in th simulation that solvs for two variabls, turbulnt kintic nrgy, K and rat of dissipation of kintic nrgy, Epsilon. Th SKE turbulnc modl was slctd bcaus of its good convnc rat and rlativly low mmory rquirmnts [5]. Th boundary conditions wr st according to th vlocitis, prssurs, tmpraturs and dnsitis, similar to th physical Vnturi tubs bing usd in th ntal t for ach of th t points. Poin t Tabl : matrix for 00 mm Vnturi tub ur mpratur Flowrat Nitrog n dnsity (-) (bar) ( C) (m /h) kg/m m/s suprfici al vlocity Poi nt Tabl : matrix for 50 mm Vnturi tub Nitrog mp ur n ratur Flowr suprficial dnsit at vlocity y (-) (bar) ( C) (m /h) kg/m m/s Computational stup Th modl consid of th intrnal sction of th Vnturi tub. Th inflation at th intrnal wall of th tub was usd in th mshing to gain bttr dtails of th prssur diribution nar th wall, as givn in Fig.. As part of grid indpndnc chck, th modl was simulatd for diffrnt msh siz from coars to fin so as to assur that thr will not b any chang in th solution by furthr rfining th msh. Fig. : Inflation layrs clos to th intrnal wall Comparativ invigation Th discha coffic obtaind from numrical simulation for Vnturi tub inalld with 0D was fir compard again th discha coffic obtaind from ntal t. This comparison was usd as th baslin rfrnc for th nxt phas of th numrical simulation analysis. Th nxt phas of th numrical simulation focusd on procssing th rsults for Vnturi tub inalld with D. Th discha coffic obtaind from th simulation for shortr wr thn compard again th discha coffic obtaind from simulation for 0D. Th impact on th chang of intrnal pip diamtr, vlocity and prssur wr also rcordd and compard.. RESULTS AND DISCUSSION Th numrical simulation rsults indicat th discha coffics btwn Vnturi tub with 0D upram raight lngth and Vnturi tub with D ar within +/-0.5% rror (uncrtainty), as shown in Tabl 5. Contours for vlocitis and prssur diributions Figurs Fig.,,, 5, 6, 7, 8 and 9 ar th vlocity contours for all th configurations of th and Vnturi tubs sizs. Flow dirction for all th contours ar from lft to right. Vlocity valus rcordd from th contours blow ar usd to calculat th volumtric flow rats. 0- colors lgnd has bn usd to nsur th diffrnt vlocitis can b mad visibl.

Sci.Int.(Lahor),9(5),5-,07 ISSN 0-56;CODEN: SINTE 8 7 Fig.

6 : Vlocity contour for 00 mm Vnturi tub with D Fig.

: Vlocity contour for 50 mm Vnturi tub with 0D Fig.

9: Vlocity contour for 50 mm Vnturi tub with D

3 Sci.Int.(Lahor),9(5),5-,07 ISSN 0-56;CODEN: SINTE 8 7 Fig. : Vlocity contour for 00 mm Vnturi tub with 0D Fig. 6: Vlocity contour for 00 mm Vnturi tub with 0D Fig. : Vlocity contour for 00 mm Vnturi tub with D Fig. 7: Vlocity contour for 00 mm Vnturi tub with D Fig. : Vlocity contour for 50 mm Vnturi tub with 0D Fig. 8: Vlocity contour for 50 mm Vnturi tub with 0D Fig. 5: Vlocity contour for 50 mm Vnturi tub with D Fig. 9: Vlocity contour for 50 mm Vnturi tub with D

4 8 ISSN 0-56;CODEN: SINTE 8 Sci.Int.(Lahor),9(5),5-,07 Figurs Fig. 0,,,,, 5, 6 and 7 ar th prssur diribution contours for all th configurations of th and Vnturi tubs sizs. Flow dirction for all th contours ar from lft to right. ur valus rcordd, at th upram of th Vnturi and at its throat, from th contours blow ar usd in th flow calculations. 0-colors lgnd has bn usd to nsur th diffrnt vlocitis can b mad visibl. Fig. : ur diribution contour for 50 mm Vnturi tub with D Fig. 0: ur diribution contour for 00 mm Vnturi tub with 0D Fig. : ur diribution contour for 00 mm Vnturi tub with 0D Fig. : ur diribution contour for 00 mm Vnturi tub with D Fig. 5: ur diribution contour for 00 mm Vnturi tub with D Fig. : ur diribution contour for 50 mm Vnturi tub with 0D Fig. 6: ur diribution contour for 50 mm Vnturi tub with 0D

5 Sci.Int.(Lahor),9(5),5-,07 ISSN 0-56;CODEN: SINTE 8 9 Fig. 7: ur diribution contour for 50 mm Vnturi tub with D coffics from numrical simulation Tabl 5, 6, 7 and 8 provid th discha coffics, calculatd using th outputs of th numrical simulation for Vnturi tubs with 0D. Th avrag valus of ths discha coffics ar compard again th discha coffic valus from ntal, and this comparison is tabulatd in Tabl 9. For Vnturi tubs sizs 00 mm, 50 mm and 00 mm, it is clarly shown that th discha coffic rror dcrass with th incras in vlocity. Viscosity and dnsity ar kpt within small variancs for all ths cass. On th basis on ths computations, it is clar that th discha coffic is a function of Rynolds numbr [6]. Th chang in th Vnturi tubs siz dos not impact th discha coffic rror trnd. For 50 mm Vnturi tub, diffrnt trnding shown in th discha coffic rror is du to th clos vlocity cass slctd for th t. Tabl 5: coffic for 00 mm Vnturi with 0D Dp ur % % % % Tabl 6: coffic for 50 mm Vnturi with 0D Dp ur % 0.6% 0.7% 0.7% Tabl 7: coffic for 00 mm Vnturi with 0D Dp ur % % % % Tabl 8: coffic for 50 mm Vnturi with 0D Dp ur % % % %

6 0 ISSN 0-56;CODEN: SINTE 8 Sci.Int.(Lahor),9(5),5-,07 Tabl 9: Comparison btwn ntal and numrical simulation (0D upram) Vnturi siz nt ANSYS (%) 00 mm % 50 mm % 00 mm % 50 mm % Tabl 0,, and provid th discha coffics, calculatd using th outputs of th numrical simulation for Vnturi tubs with D. Th avrag valus of ths discha coffics ar compard again th discha coffic valus from ntal, and this comparison is tabulatd in Tabl. Tabl 0: coffic for 00 mm Vnturi with D Dp ur % % % % Tabl : coffic for 50 mm Vnturi with D Dp ur % % % % Tabl : coffic for 00 mm Vnturi with D Dp ur % % % % Tabl : coffic for 50 mm Vnturi with D Dp ur % % % % Tabl : Comparison btwn ntal and numrical simulation (D upram) Vnturi siz nt ANSYS (%) 00 mm % 50 mm % 00 mm % 50 mm % For Vnturi tubs sizs 00 mm, 50 mm and 00 mm with D, similar trnd whrby th discha coffic rror dcrass with th incras in vlocity is shown for ths sizs, xcpt for th 50 mm siz.

7 Sci.Int.(Lahor),9(5),5-,07 ISSN 0-56;CODEN: SINTE 8 It is clarly shown that th discha coffic rror is lar for th Vnturi tubs with D whn compard with th ntal discha coffic. This supports th gnral guidlin that having shortr upram lngth will incras th discha coffic rror. Tabl 5 compars th discha coffics obtaind from Vnturi tub with 0D and Vnturi tub with D numrical simulation. It is shown that th discha coffic rrors btwn th two sts of data ar wll within +/-0.5% as xpctd, similar to th ISO 567- guidlin. Howvr, it is also shown that ths rrors can b biasd to positiv rror or ngativ rror. Earlir in this papr, it was indicatd that th siz of th Vnturi tub dos not impact th discha coffic rror. Th discha coffic rror trnd shown in Tabl 5 indicats that prssur contributs to th bias in rror. It is shown that low prssur (approximatly bar) for Vnturi sizs 00 mm and 50 mm givs positiv bias discha coffic rror, and high prssur (approximatly 50 bar and 60 bar) for Vnturi sizs 00 mm and 50 mm givs ngativ bias discha coffic rror. Tabl 5: Comparison btwn D and 0D upram of th numrical simulations Vnturi siz Cd (0D upram) Cd (D upram) (%) 00 mm % 50 mm % 00 mm % 50 mm % 5. CONCLUSION Th numrical simulation can b usd in th dsign for optimum solution whnvr availabl upram raight lngth is insuffic for high accuracy inallation as rsults from this work indicat th discha coffics btwn Vnturi tub with 0D and Vnturi tub with D ar within +/-0.5% rror (uncrtainty). Although th Vnturi sizs do not impact th rror in th discha coffic, vlocity and prssur of th procss trmndously affct th accuracy of th masurmnt. 6. ACKNOWLEDGEMENTS Authors acknowldg th assianc from FRGS grant 556, as wll as support from NEL. 7. REFERENCES [] Himp, U., Gott, B. and Schatz, M. Influnc of upram bnds on th discha coffics of classical Vnturi tubs and orific plats. Flow masurmnt inrumnt 99, Vol. 5 No. : 09-6 (99). [] Radr-Harris, M.J., Sattary, J.A. and Sparman, E.P., 995. Orific plat discha coffic quation furthr work. Flow masurmnt and inrumntation 6: 0- (995). [] Intrnational Organization for Standardization, 00. Masurmnt of fluid flow by mans of prssur diffrntial dvics insrtd in circular cross-sction conduits running full, Part : Vnturi tubs. BS EN ISO 567- (00). [] Fang, L. and Zhang, T., 008. Chins Journal of Chmical Enginring, 6: 0-; [5] Sowjanya, V. and Ji, C. Applid Mathmatical Modlling, : (00). [6] Sattary, J.A. and Radr-Harris, M.J. North Sa Flow Masurmnt Workshop, Papr.6 (997).

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