CFD MODELING FOR HELIUM RELEASES IN A PRIVATE GARAGE WITHOUT FORCED VENTILATION

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1 CFD MODELING FOR HELIUM RELEASES IN A PRIVATE GARAGE WITHOUT FORCED VENTILATION Papankolao, E.A. 1 and Venesanos, A.G. 1 1 Envronmenal Research Laboraory, NCSR Demokros, Agha Paraskev, Aks, 15310, Greece, e-mal: venes@pa.demokros.gr ABSTRACT In he corse owards a safe fre hydrogen based socey, one of he asks o be consdered s he nvesgaon of he condons nder whch he se or sorage of hydrogen sysems nsde bldngs becomes oo dangeros o be acceped. One of he relevan scenaros, whch s epeced o have a relavely hgh rsk, s a slow (and long lasng) hydrogen release from a vehcle sored n a closed prvae garage who any forced venlaon,.e. only wh naral venlaon. Ths scenaro has been earler nvesgaed epermenally (by M. Swan), sng He (helm) o smlae he hydrogen behavor. In he presen work he CFD code ADREA-HF s sed o smlae hree of he abovemenoned epermens, sng he sandard k-ε rblence model. For each case modeled he predced concenraon (by vol.) me seres are compared agans he epermenal a he gven sensor locaons. In addon he srcre of he flow s nvesgaed by presenng he helm concenraon feld. NOMENCLATURE Upper-case Roman P Pressre (Pa) R Specfc gas consan of speces (J kmol -1 K -1 ) T Temperare (K) Lower-case Roman d Moleclar dffsvy of helm o ar (m 2 s -1 ) g Gravy acceleraon n he -drecon (m s -2 ) k Trblen knec energy (m 2 s -2 ) q 1, q 2 Mass fracon of componen 1, 2 (-) Tme (s) componen of velocy (m s -1 ) Normalzed parallel o wall velocy (-) Caresan co-ordnae (m) y Normalzed dsance from he wall (-) y Dsance of crren node o neares sold srface (m) z Caresan z co-ordnae (m) Lower-case Greek ε Trblen energy dsspaon rae (m 2 s -3 ) κ von Karman consan (-), Lamnar and rblen vscosy (kg m -1 s -1 ), Mre densy, -componen densy (kg m -3 ) σ Τrblen Schmd and Prandl nmber (-) τ w Wall shear sress (N m -2 ) 1.0 INTRODUCTION In he corse owards a safe fre hydrogen based socey, one of he asks o be consdered s he nvesgaon of he condons nder whch he se or sorage of hydrogen sysems nsde bldngs becomes oo dangeros o be acceped. The drafng of he assocaed recommendaons/gdelnes s oday one of he man goals of he HYSAFE proec ( a goal planned o be mplemened hrogh he InsHyDe nernal (o HYSAFE) proec.

2 In he pas, smlar work has been performed for naral gas aomove applcaons. Gran e al. (1991) [1] eamned he hazard assessmen of naral gas vehcles n pblc parkng garages, by applyng he PHOENICS CFD code. Mrphy e al. (1992) [2] eamned he een of ndoor flammable plmes reslng from CNG bs fels sysem leaks n rans manenance and sorage facles by applyng he FLUENT CFD code. Refocsng on hydrogen sysems, Swan e al. (1998) [3] condced a large combned epermenal- CFD research program, n an effor o deermne he venlaon reqremens of hydrogen felled vehcles sorage n resdenal garages. The epermens were done wh a fll-scale model of a sngle car garage conanng a fll scale model of a vehcle wh smlaed leakage of hydrogen (sng helm) a a rae of 7,200 L/hr. The fll-scale garage and vehcle model was bl ndoors o elmnae he varaons of wnd and odoor emperare. The prncpal qeson beng addressed n hs work was, how shold esng garages be modfed o make hem sable for hydrogen felled vehcle sorage. The order of preference for garage modfcaons was modfcaon of garage door who sng forced venlaon, modfcaon of garage who sng forced venlaon (addon of a passve ven a he garage celng) and las modfcaon of garage sng forced venlaon and addon of a hydrogen leak deecon sysem. The CFD calclaons were performed sng FLUENT. Comper modelng done hrogho he work showed ha he dfference n hydrogen and helm concenraons n resemblng geomeres rarely ogoes 15%. In addon, he larges dfferences occr drng he ransen perod before seady sae and before he hghes concenraons are acheved. Laer on Swan e al. (1999) [4] performed hydrogen dsperson epermens n smple vened enclosres and assocaed CFD valdaon sng he FLUENT code. Recenly Agrana e al. (2004) [5] smlaed he vened hallway epermen sng he PHOENICS code and fond resls smlar o he FLUENT code. In anoher work Breng e al. (2001) [6] appled he GASFLOW CFD code o calclae he emporal and spaal dsrbon of hydrogen and crera o evalae he flame acceleraon and deonaon poenal n an effor o esmae he combson hazard, de o he bol-off from he cryogenc hydrogen ank of a car n a prvae garage. Recenly Parsons and Brnckerhoff (2004) [7] evalaed he facly modfcaons and assocaed ncremenal coss ha may be necessary o safely accommodae hydrogen fel cell vehcles n for sppor facly case sdes: commercal ml-sory above-grond parkng, commercal ml-sory below-grond parkng, resdenal wo vehcle garages and commercal manenance/repar/servce saon. The mehodology appled was also CFD. The above menoned revew of prevos work shows ha he CFD approach s he commonly appled mehodology. On he oher hand he specfc scenaros consdered ofen nclde slow flow condons (lamnar or ransonal), for whch he choce of rblence model s non rval. Addonal ncerany can also be nrodced by he selecon of he grd resolon and he bondary condons. Clearly here s a need o develop CFD pracce gdelnes for sch knd of flows. The presen work focses on he abovemenoned helm epermens by Swan e al. [3]. Three of hese ess were seleced for smlaon sng he ADREA-HF CFD code [8]. The sandard k-ε model [9] was seleced for rblence, n order o assess s performance nder he specfc epermenal condons. For each case modeled he predced concenraons (by vol.) are compared agans he epermenal a he gven sensor locaons. In addon he srcre of he flow s nvesgaed by presenng he predced helm concenraon feld. 2.0 EXPERIMENTAL DESCRIPTION Fgre 1 shows he geomery of he epermenal facly. A fll scale sngle car garage was sed. Two vens were nsalled on he garage door. The frs ven locaon was s a he boom of he door whle he second ven was locaed a s op. In he epermens dfferen doble ven garage door geomeres

3 were esed. In all cases he vens eended he wdh of he garage door. A fll-scale plywood model vehcle (roghly followng he dmensons of a Ford Tars) was placed nsde he garage. The wheels were represened by recanglar boes. Fgre 1. The geomery of he epermenal facly (lef). The locaon of he sensors (rgh) All esng was done wh helm. Helm flow rae was se a 7,200 L/hr whle s release lased 2 hors. The leak locaon was a he boom of he vehcle and cenered a s wdh. The sensors were locaed a he for corners of he garage. Fgre 1 shows he locaon of he for sensors. Table 1 lss he geomery dmensons of he epermenal facly n SI ns. Vehcle locaon and sze (4 wheels, body, chnk and 2 wedges) Table 1. The geomery dmensons of he epermenal facly X (m) Y (m) Z (m) Garage sze Body locaon Body sze Wedge 1 locaon Wedge 1 sze Wedge 2 locaon Wedge 2 sze Chnk locaon Chnk sze Wheel 1 locaon Wheel 1 sze Wheel 2 locaon Wheel 2 sze Wheel 3 locaon Wheel 3 sze Wheel 4 locaon Wheel 4 sze Garage door locaon Garage door sze Sensor 1 locaon Sensor 2 locaon Sensor 3 locaon Sensor 4 locaon Upper ven locaon Upper ven sze Lower ven locaon Lower ven sze Depends on each case 0.00 Depends on each case

4 Leak locaon Leak sze The followng hree cases were smlaed dependng on he hegh of he vens: Case 1: 2.5 nches (6.35 cm) op and 2.5 nches boom door vens Case 2: 9.5 nches (24.13 cm) op and 9.5 nches boom door vens Case 3: 19.5 nches (49.53 cm) op and 19.5 nches boom door vens 3.0 MATHEMATICAL FORMULATION The mng of helm wh ar was calclaed by solvng he hree dmensonal ransen, flly compressble conservaon eqaons for mre mass (conny eqaon), mre momenm (hree veloces) and helm mass fracon: Mre mass (conny eqaon) = 0 (1) Mre momenm ( ) = g P (2) Helm mass fracon = q d q q σ (3) In he above eqaons he mre densy s relaed o componen denses (1 for helm and 2 for ar) and mass fracons hrogh q q = ; 1=q1 q 2 (4) For he componen denses he deal gas law was assmed vald. R T P = (5) Trblence was modeled sng he sandard k-ε model, n whch boyancy effecs were nclded. In hs model rblen vscosy s calclaed from he followng eqaons: /ε 2 k C =, where C =0.09 (6) The rblen knec energy s obaned from he followng ranspor eqaon: ε σ = B k G G k k k, where σ k =1.0 (7)

5 The volmerc prodcon rae of k by shear forces, G and he boyancy prodcon (desrcon) erm, G B are gven by: G= ) ( ; G B g z = (8) σ z The dsspaon rae of he rblen knec energy s obaned from he followng ranspor eqaon: ε ε = ε ε σ ε k [ C ( G C G ) ε] 1 3 B C2 Where σ ε, C 1, C 2 and C 3 are consans havng vales 1.3, 1.44, 1.92, and 1.0 respecvely. (9) Fnally he moleclar dffsvy of helm o ar was aken o be d= m 2 s -1 as n [4] and he rblen Schmd and Prandl nmber σ = COMPUTATIONAL DOMAIN AND GRID Gven he geomery of he epermenal facly and he locaon of he leak, was assmed ha -z plane symmery ess. Therefore, half he wdh of he geomery was aken no accon. Addonally, he compaonal doman was seleced o eend beyond he bondary of he garage, see fgre 2. Ths was done o avod he ncerany assocaed wh specfcaon of bondary condons a he door vens and concenrae more on he assessmen of he rblence model. The presen approach clearly reqres more compaonal effor, b s on he oher hand he frs sep owards developng CFD gdelnes for ven openngs modelng, a ask whch s lef for fre work. The compaonal grd was Caresan and s man characerscs are smmarzed n Table 2. Fgre 2 shows he y-z grd for Cases 1, 2, 3 and he -z grd for Case 1. As can be observed, grd refnemen was sed close o he door s openngs (vens), he sorce and he walls. The grd becomes coarser as eends far from he facly. In general he mamm grd epanson rao was 1.2 whle s mnmm was I can also be observed ha he wo wedges of he car c he grd n an rreglar manner. Ths was handled sng he porosy formlaon, whch classfes he cells no flly acve (porosy 1), nacve (porosy 0) and parally acve (porosy beween 0 and 1). The geomercal preprocessng, ncldng he calclaon of he poroses was performed sng he DELTA-B code [10]. Table 2: The compaonal grd man characerscs Case Grd dmensons Nmber of acve cells , , ,552 Mn-ma cell sze n z-dr. (m) 0.04 close o sorce m a he op of doman close o sorce m a he op of doman m close o he grond m a he op of doman Mn-ma cell sze n -dr. (m) 0.02 close o door 0.92 a he end of doman Mn-ma cell sze n y-dr. (m) 0.1 close o sorce and symmery plane a he begnnng of he doman

6 Fgre 2. Above: Case 1, below: Case 2 lef and Case 3 rgh 5.0 INITIAL AND BOUNDARY CONDITIONS Bondary condons on sold srfaces were zero-graden for he helm mass fracon whle he followng wall fncons for velocy (parallel o wall componen), rblen knec energy and dsspaon rae were appled: y 1 ln(9 y κ = ) y y < 11.6 ; > 11.6 k ; = C * 3 k 4 = C (10) κy ε Symmery bondary condons were appled a he symmery plane,.e. zero-graden for all varables ecep normal velocy, whch was se eqal o zero. Inflow bondary condons were specfed a he sorce,.e. gven velocy (0.1 m s -1 normal and 0.0 for oher componens), helm mass fracon (1.0), pressre (101,325 Pa), rblen knec energy (0.0) and dsspaon rae (0.0). Addonally, a zero-graden was appled for all varables a he sorce, mplyng no dffson across he sorce srface. 3 2

7 Bondary condons a he remanng open srfaces of he doman (.e. ecep symmery plane and sorce) were se as follows: For he normal veloces zero-graden was assmed a he laeral srfaces. A he op srface normal veloces were obaned from he conny eqaon, assmng gven consan pressre a he neghborng cells. For he oher varables he bondary condon was a fncon of he flow drecon: Zero-graden was assmed f he flow was dreced owards and gven vale (eqal o he one esng a me 0) was appled when he flow was dreced nwards. Regardng nal condons, he wnd velocy was se o zero, wh no rblence, emperare K and hydrosac pressre. 6.0 NUMERICAL OPTIONS The ADREA-HF code employs he conrol volme dscrezaon mehod, wh saggered grd arrangemen for he veloces [11]. The frs order flly mplc scheme was sed for me negraon. The frs order pwnd scheme was sed for dscrezaon of he convecve erms. The calclaons were performed wh an Inel Xeon CPU 3.60GHz wh Wndows operang sysem. Fgre 3 presens he reqred CPU mes for all hree cases. The calclaons were performed for a oal real me of 7,200 seconds. ADREA-HF has an aomac me sep selecon mechansm. If he convergence error s above he mamm allowed, he solon s repeaed sng a smaller me sep. In all cases he nal me sep was se o seconds. In all cases he mamm permed me sep was se o 0.1 seconds. Ths mamm was reached very early,.e. whn he frs 2.8, 1.8 and 1.3 seconds for Cases 1, 2 and 3 respecvely and remaned consan nl he end of he rns. From fgre 3 can be observed ha as he ven sze ncreases, he reqred CPU me slghly decreases. 7.5E05 Comparson of CPU me 5.0E05 Tme (sec) 2.5E05 0.0E00 Case 1 Case 2 Case RESULTS AND DISCUSSION Fgre 3. Comparson of CPU mes beween he hree cases Fgre 4 shows he predced conors of helm concenraon (by vol.) a he symmery plane a 3,600 seconds from he begnnng of he release for Case 1. As can be observed, he ven a he boom of he door provdes a flow of fresh ar near he floor, flowng nder he vehcle. The ven a he op of he door provdes an e for he low densy gas mre of ar and helm, near he celng. The se of pper and lower ven prodces venlaon ha lms he sze of he combsble gas clod o a small poron nder he fron of he vehcle whch eends n he z-drecon n fron of he vehcle. The res of he garage gas remaned leaner han he lean lm of combson for H 2. I shold be noed ha for H 2 he pward propagang lean lm of combson s 4.1% whle s downward propagang lean lm of combson s 10%. The smalles helm concenraon s locaed near he floor and he door of he garage de o he fresh ar nflow from he boom ven.

8 Fgre 4: Conors of He concenraon (by vol.) a symmery plane a =3,600 sec (Case 1) Fgre 5 shows he predced He concenraon verss he measred ones a he for sensor locaons for Case 1. As can be seen, he predced He concenraons agree well wh he epermenal daa for sensors 2 and 3, whle here s an overesmaon for sensors 1 and 4. The reslng predced concenraon dfference beween op and lower sensors s nderesmaed. Ths cold be arbed o he rblence model overesmang he rblen mng. Fgre 5. Predced verss epermenal concenraons (by vol.) a he sensor locaons (Case 1) Fgre 6 shows he conors of helm concenraon n he -z symmery plane a 3,600 seconds from he begnnng of he release for Case 2. The same observaons as n Case 1 can be made for hs case oo. The dense ar enerng he boom ven raveled nder he vehcle oward s fron. The ar replaces he mre, rch n helm, gas rsng from nderneah he fron of he vehcle. The mamm helm concenraon s locaed near he sorce whle he gas mre eng he garage s movng pwards n a colmn-lke shape. Agan, he colmn broadens wh hegh. A comparson beween Case 1 and Case 2 shows ha he colmn-lke pward movng mre s broader for Case 2 whch means ha more mre gas s leavng he garage n hs case. Frhermore, mos of he garage gas remaned leaner han he lean lm of combson for H 2 (4.1%) whle he ncrease of he ven sze resled n a combsble clod from he leak ha dd no eend far beyond he ndersde of he fron of he

9 vehcle. I shold be noed ha now he ven szes are almos 4 mes broader han n Case 1. A comparson of helm volmerc concenraon n he -z symmery plane a varos mes afer he 3,600 seconds shows ha he flow paern has reached seady sae condons a leas a 3,600 seconds. Fgre 6. Conors of He concenraon (by vol.) a symmery plane a =3,600 sec (Case 2) Fgre 7 shows he predced He concenraon verss he measred ones a he for sensor locaons for Case 2. As can be observed, he predced He concenraons are n sasfacory agreemen wh he epermenal daa for all sensors. The fgre shows a small over predcon for sensors 2, 3 and 4 and a small nder predcon for sensor 1. Fgre 7. Predced verss epermenal concenraons (by vol.) a he sensor locaons (Case 2) Fgre 8 shows he conors of helm concenraons n he -z symmery plane a 3,600 seconds from he begnnng of he release of he hrd case. The same observaons as n cases 1 and 2 can be made for hs case oo. A comparson beween Fgres 4, 6 and 8 shows ha as he sze of he openngs redces less gas s leavng he garage. The colmn of he oflow gas s mch broader n hs case. Conseqenly, lower helm concenraons es nsde he garage. The mamm helm concenraon s locaed a he sorce b now occpes less space. A comparson of helm

10 volmerc concenraon n he -z symmery plane a varos mes afer he 3,600 seconds shows ha he flow paern has reached seady sae condons a leas a 3,600 seconds. Fgre 8. Conors of He concenraon (by vol.) a symmery plane a =3,600 sec (Case 3) Fgre 9 shows he predced He concenraon verss he measred ones a he for sensor locaons for Case 3. As can be observed, he predced He concenraons are nderesmaed for sensors 1, 2 and 3. A small over predcon s also observed for sensor 4. Fgre 9 sggess ha he predced naral venlaon rae s overesmaed. Fgre 9. Predced verss epermenal concenraons (by vol.) a he sensor locaons (Case 3) 8.0 CONCLUSIONS The ADREA-HF CFD code was sccessflly appled o smlae hree fll scale helm release epermens n a prvae garage [3], sng he sandard k-ε rblence model. The predced He concenraons (by vol.) me seres were compared agans he measred ones a he for epermenal sensor locaons. The predced resls were fond generally n accepable agreemen wh he epermen. For he case wh he lowes ven sze he vercal concenraon graden was fond

11 nderesmaed compared o he epermen. Ths was arbed o he rblence model overesmang mng nder he gven low flow condons. Addonally, he calclaons revealed he mng paerns and showed ha he mng mechansms reached a near-eqlbrm sae reslng n a consan clod sze and shape drng he release perod. Fnally, he performed calclaons nderlne he mporance of applyng he CFD mehodology o evalae he poenal hazards especally nder comple release condons. 9.0 ACKNOWLEDGEMENTS The ahors wold lke o hank he Greek Secreara of Research and Technology as well as he Eropean Commsson for fndng of hs work hrogh he 02-PRAKSE-42 and HYSAFE-NoE proecs respecvely REFERENCES 1. Gran, T.J., Shaaban, S.H. and Zalak, V.M., Hazard assessmen of naral gas vehcles n pblc parkng garages, Fnal Repor, work performed by Ebasco Servces Inc. for he Brooklyn Unon Gas Company, Mrphy, M.J., Brown, S.T. and D.B. Phlps, Een of ndoor flammable plmes reslng from CNG bs fels sysem leaks, Inernaonal Trck and Bs meeng and eposon, Toledo, Oho, US, November 16-19, 1992 (SAE echncal paper No ). 3. Swan, M.R., Grllo, E. S. and M.N. Swan, Phase 2: Rsks n ndoor vehcle sorage, n Addendm o Hydrogen Vehcle Safey Repor: Resdenal Garage Safey Assessmen, analyss condced by: Mchael R. Swan, Unversy of Mam, nder sbconrac o Dreced Technologes Inc, prepared for he Ford moor company nder prme Conrac No. DE-AC02-94CE50389 o he U.S. Deparmen of Energy, Offce of Transporaon Technologes, Ags Swan, M.R., Grllo, E. S. and M.N. Swan: Epermenal verfcaon of a hydrogen rsk assessmen mehod, Chemcal Healh and Safey, 1999, pp Agrana, V., Cheng, Z. and Tchovelev, A., CFD Modelng of Hydrogen Releases and Dsperson n Hydrogen Energy Saon, Proceedng of WHEC-15, 2004, Yokohama. 6. Breng, W., Necker, G., Kap, B. and Veser, A., Nmercal smlaon of hydrogen n a prvae garage, Proceedngs of he forh nernaonal symposm on hydrogen power heorecal and engneerng solons Hypohess IV, Sralsnd (Germany), 9-14 Sepember Sppor facles for hydrogen felled vehcles-concepal desgn and cos analyss sdy, Techncal repor, 2004, Prepared for Calforna Fel Cell Parnershp by Parsons and Brnckerhoff n assocaon wh TIAX and Unversy of Mam. 8. Barzs, J. G., ADREA-HF: A hree dmensonal fne volme code for vapor clod dsperson n comple erran, EUR repor EN, Lander, B. E. and Spaldng, D. B., The nmercal compaon of rblen flow, Comper Mehods n Appled Mechancs and Engneerng, 3, Isse 2, pp Venesanos, A. G., Casaros, N., Würz, J. and Barzs, J. G., The DELTA_B code. A comper code for he smlaon of he geomery of hree-dmensonal bldngs. Code srcre and sers manal, EUR repor EN. 11. Paankar, S. V., Nmercal hea ransfer and fld flow, 1980, Hemsphere Pblshng Corporaon.