Design and Development of a Closed Two Loop Thermal Management Configuration for PEM Fuel Cell

Transcription

1 2012 2nd Interntionl Conference on Environment nd Industril Innovtion IPCBEE vol35 (2012) (2012) IACSIT Press, Singpore Design nd Development of Closed Two Loop Therml Mngement Configurtion for PEM Fuel Cell B Viswnth Ssnk 1,+, NRjlkshmi 1, KSDhththreyn 1 1 Center for Fuel Cell Technology (CFCT)-ARC Interntionl, IIT-Mdrs Reserch Prk, Trmni, Chenni Indi Abstrct Therml Mngement is vitl for the sustined performnce of Polymer Electrolyte Membrne (PEM) fuel cell t its optiml operting conditions One of the impediments in developing such therml mngement system for PEM fuel cell in vehiculr pplictions is weight, volume nd prsitic power constrints of the therml mngement system An issue with closed loop system is the het ddition from fuel cell into the cooling loop This het cn be subdued by the use of het trnsfer modules like plte het exchnger (PHE) nd rditors in the loop In the present study therml mngement system is designed which cn remove het from the fuel cell to mbient effectively nd llow the stck to operte t pek power of 15kW elec conditions for more thn 60 minutes of durtion Coolnt flow rte optimiztion nd therml mngement configurtion design re conducted to increse the het trnsfer from fuel cell The verge therml power removed by the coolnt from cell for ll the therml mngement configurtions is clculted A reltion between the verge therml power, flow rte nd therml mngement circuit hs been estblished Keywords: PEM fuel cell, therml mngement, cooling loop, coolnt, Plte Het Exchnger, Rditor 1 Introduction Therml mngement of PEMFC system hs been pivotl fctor to ensure high performnce nd efficiency of the cell Aprt from electricity & wter, het is nother byproduct produced by the cell which is emnted during the electrochemicl rection between hydrogen nd oxygen [1] Severl issues re ssocited with the therml mngement of PEMFC for which temperture ply mjor role s discussed by Kndlikr et l [2]The temperture rise nd its distribution re completely dependent on the mount of het retined by the stck Severl effective techniques hve been investigted for the het removl such s free ir brething nd ir cooling techniques [3-5] which hve some limittions with respect to the cpcity, size etc, However liquid coolnt system is preferred over ir becuse of coolnts lrger specific het cpcity The vrious het generting sources in fuel Cell nd the mode of het trnsfer from cell to severl sources like coolnts, recting gses nd mbient ir with governing equtions re discussed briefly by Shn et l [6] Zong et l [7] discussed the het trnsfer from the stck to the coolnt flowing through the cell nd the dependence of coolnt temperture on the overll stck temperture The coolnt bsorbed het from the stck by convection nd its temperture is ssumed to be constnt cross the cell However the flow rte of the coolnt through the cell is lso n importnt prmeter in mintining the temperture of the stck which is discussed in present study The coolnts used in removing het from fuel cell stck re required to be cooled to ensure tht the coolnt enters the stck t desired temperture Severl designs where vrious cooling pprtus for cooling the coolnt flowing thorough fuel cell hve been discussed [8-10] Effective use of vrious het trnsfer modules like rditors nd het exchngers is required to ensure tht the fuel cell is mintined t its optiml conditions for long durtion of time Dohoy Jung et l [11] described the need for mintining of the temperture of the fuel cell t its optiml operting conditions nd refers to the use of + Corresponding Author Tel: ; fx: E-mil ddress:bssnk@gmilcom 120

2 rditor fn ssembly to cool the coolnt The mount of het generted inside fuel cell depends on the het removed by the coolnt flowing through it Pndiyn et l [12] discussed the het trnsfer through the fuel cell, quntifiction of the het removed from the cell nd the sources of het genertion The present study ddresses the two mjor vrints viz, flow rte nd temperture of the coolnt in developing two loop cooling system for 15 kw fuel cell stck Further n effective therml circuit which optimizes the stck performnce for longer durtions with less volume of coolnt use is identified 2 Experimentl A closed single loop nd two loop therml mngement systems were developed for cooling of the fuel cell stck of 15 kw elec pek power In the closed loop configurtion, coolnt wter ws flowing through the fuel cell stck from reserve tnk which holds fixed volume of 10 liters of coolnt wter Thermocouples were inserted t the primry coolnt inlet, outlet of coolnt from the stck nd one inserted on the stck for mesuring tempertures In the two loop therml mngement systems there exists secondry cooling circuit consisting of reserve tnk to hold nother fixed volume of 10 liters of coolnt wter, nd plte het exchnger (PHE) to exchnge het between the primry nd secondry loops A rditor/ fn ssembly ws used in ll the three different therml mngement configurtions R, R p nd R s to remove the excess het in the cooling circuit by convection into the mbient Temperture of the primry coolnt inlet nd outlet were mesured nd the verge therml power removed by coolnt from the fuel cell stck ws evluted The fuel cell stck temperture ws monitored for the sustined performnce t the optiml operting conditions nd pek power Nottions: R: Therml Mngement system with single loop nd rditor/fn ssembly Rp: Therml Mngement system with two loop, plte het exchnger nd rditor/fn ssembly in primry loop Rs: Therml Mngement system with two loop, plte het exchnger nd rditor/fn ssembly in secondry loop (see Fig 1 for R s configurtion schemtic exmple) 3 Results nd Discussion Firstly the fuel cell performnce is evluted from its operting temperture In the present study it is desired tht the therml mngement system removes surplus het out of the fuel cell, t its pek power conditions nd mintin the stck temperture round 50 C Initilly with single loop therml mngement system R, rditor employed, with primry coolnt flow rte mintined t 25 lpm, it cn be seen tht the fuel cell stck reched the threshold temperture of 50 C in less thn 25 minutes [Fig 2] This lower durtion in using R is due to the greter het ccumultion in the primry loop tnk In order to reduce the het ugmenttion in the primry loop, het trnsfer modules were introduced, viz, PHE between primry nd secondry loops for trnsferring some mount of het content from primry to secondry loop The flow rte in the primry loop is vried between 25 lpm nd 35 lpm keeping the secondry coolnt flow rte t constnt 45 lpm The corresponding fuel cell temperture profiles re shown in Fig 2, where it is evident tht the R p configurtion with 35 lpm flow rte llowed the stck to operte t the pek power conditions for more thn 60 minutes nd mintining its temperture round 50 C It ws not possible to mintin the stck temperture round 50 C for longer durtion with other configurtions However it is required tht this conclusion is justified further by studying the het profiles nd their distributions for ll the therml mngement configurtions 121

3 Fig1: Rs configurtion Schemtic Fig2: Stck Temperture profile 31 Het removl from the fuel cell The mount of het generted by fuel cell during its opertion is round 12 to 15 times of the electricl power generted depending on the voltge t which the cells re operted Surplus het inside the fuel cell needs to be removed in order to mintin the stck temperture under optimum rnge The coolnt wter flowing through the fuel cell removes this surplus het The mount of het thus removed by the primry coolnt is given in Eqn1 = mc pδt (1) Where,, ṁ, c p nd Δ T corresponds to the quntity of het removed from the stck, mss flow rte of the primry coolnt, specific het of wter nd the temperture difference of the primry coolnt cross the fuel cell The het removed by the coolnt for ll the three configurtions is given in Fig3 It cn be observed from Fig3 tht the mximum het removed from the fuel cell is observed with R p configurtion with 35 lpm of primry coolnt flow rte Also the het removl distribution extended to more thn 60 minutes of the fuel cell opertion Greter flow rte of primry coolnt resulted in greter het removl However the het distribution over n extent is defined by the primry coolnt inlet temperture s shown in Fig4 As cn be seen from Fig4 tht s long s the primry coolnt temperture could be mintined below of 40 C t given flow rte, the stck cn lso be mintined round 50 C s shown in Fig2 Fig3: Het removl from fuel cell profile Fig4: Primry coolnt inlet temperture profile 122

4 32 Het trnsfer cross the Plte Het Exchnger The heted primry coolnt exiting the Fuel Cell is pssed through plte het exchnger for het exchnge with the secondry coolnt The net het trnsfer cross the het exchnger cn be clculted from three different pproches nmely (i) het lost by the primry coolnt cross the het exchnger (ii) het gined by the secondry coolnt cross the het exchnger (iii) het trnsfer cross the het exchnger using the men temperture difference s given in Eqn2 [13] = m p c pδtp = m s c pδts = UAΔT (2) Here ṁ p, ṁ s, Δ T, Δ T p s,u, A, Δ T corresponds to the primry coolnt flow rte, secondry coolnt flow rte, temperture drop cross the primry coolnt, temperture gin cross the secondry coolnt, overll het trnsfer coefficient, totl het trnsfer re nd the log men temperture difference of the coolnts cross the het exchnger The overll het trnsfer cross the plte het exchnger s clculted from Eqn2 depends primrily on the temperture difference Δ T nd the overll het trnsfer coefficient U of the het exchnger The method for the clcultion of the overll is defined in the Eqns (3-6) [13] 1 U = (3) ( 1 h c + 1 h o ) Where h c nd ho re the individul het trnsfer coefficients of the cold side nd hot side of the het exchnger A generl eqution representing the individul het trnsfer coefficient is given in Eqn6 1/ 2 1/ 3 Nu L = 0664 Re L Pr (4) u L Re L = (5) ν k h = Nu L (6) L Observing the Eqns (2-6) it cn be concluded tht net het trnsfer coefficient U increses with increse in men velocity u (flow rte for the present study) of the flowing fluid This supports the observtions from Fig 2, 3&4 tht greter the flow rte of the primry coolnt, more is the het removl from stck nd greter the fuel cell opertionl durtion 33 Het trnsfer cross the rditor/fn ssembly There is need for rditor/fn ssembly s nother het trnsfer source to remove the ugmenting nd ccumulting het in the cooling loops to the mbient (het sink) The net het removl from the cooling loop by the rditor/fn ssembly is described in similr method s tht of plte het exchnger The following Eqn7 describes the vrious governing methods for clculting the overll het trnsfer from the coolnt to the mbient cross the rditor rd = m c c ΔT p c = m c ΔT = kaδt Where ṁ c, c p, Δ Tc, m, c, Δ T, k, A, Δ T represent the flow rte of the coolnt through rditor, specific het cpcity of wter, temperture drop of the coolnt cross rditor, flow rte of the ir cross the rditor, specific het cpcity of ir, temperture gin in the ir flowing cross the rditor, het trnsfer coefficient of the het trnsfer, het trnsfer re nd the log men temperture difference cross the rditor 34 Net het removl from the Primry cooling loop It cn be observed tht in the present therml mngement system, the plte het exchnger nd rditor/fn ssembly re the two het trnsfer modules to remove the het circulting in the cooling loops The im in introducing the het trnsfer modules it to remove the mximum mount of this circulting het from the primry loop to mbient However, depending on the configurtion in ppliction, the quntity of net het removed from the primry loop will be contribution from the two het trnsfer modules (7) 123

5 Het removl from R configurtion In the R configurtion, the net het removl from the primry loop is contributed from the rditor/fn ssembly lone Thus the net het removed is given by Eqn8 T Δ R = rd = ka (8) dt Het removl from R p configurtion In the R p configurtion, the net het removl from the primry loop is contributed both by the plte het exchnger nd rditor/fn ssembly only Thus the net het removed is given by Eqn9 ΔT P = rd + = kard + UAΔT (9) dt Het removl from R s configurtion In the R s configurtion, the net het removl from the primry loop is contributed from the plte het exchnger lone The rditor/fn ssembly is plced in the secondry loop nd receives het crried by the secondry loop Thus the net het removed is given in Eqn10 = UA ΔT (10) P = Thus the overll het removed from the vrious cooling loops nd its distribution over the durtion of the stck is given in Fig 5 The % of het removl from ll these configurtions is given in Tble1 Therml Configurtion Lpm Averge Tble 1 P Averge % Het removl Fuel cell durtion (minutes) R p 35 22kW 18kW 82% kW 16kW 76% 46 R s kW 16kW 475% kW 15kW R 35 19kW 125kW 65% 16 From Tble1, it is cler tht using R p configurtion with 35 lpm flow rte, 82% of ugmented het in the primry loop is relesed through the het trnsfer modules nd specificlly the rditor in the primry line, mking the fuel cell to operte for longer durtion Further work is in progress to evlute the efficient therml configurtion loop for high cpcity fuel cell stcks Further reserch cn lso be extended in understnding the behvior of vrious other coolnts by introducing them into the secondry loop nd studying their pplicbility in replcing wter s the primry coolnt Fig5 Het removl from primry loop profile 124

6 4 Conclusions It cn be concluded tht efficient therml mngement plys pivotl role in the fuel cell dynmics nd its performnce The therml mngement configurtions using plte het exchnger nd rditor fn ssembly hve been developed, which re helpful for effective het mngement in the fuel cell The cumultive het trnsfer from ll the configurtions, prmeters like flow rte of coolnt nd coolnt inlet temperture ply mjor role in the optimum design of the system It hs been observed from these studies tht the configurtion R p with rditor/fn ssembly positioned in the primry loop resulted in the mximum het removl from the fuel cell for ny given flow rte of coolnt It is concluded tht the objective of mintining the fuel cell functioning t its pek power of 15 kw elec for more thn 60 minutes is chieved using the R p configurtion with 35 lpm primry coolnt flow rte These experimentl dt coincides well with theoreticl formultions 5 Acknowledgements The uthors would like to cknowledge Dr GSundrrjn, Director ARCI for supporting this work nd Deprtment of Science nd Technology, Govt of Indi for finncil ssistnce 6 References [1] Frno Brbir, PEM Fuel Cells Theory nd Prctice, Elsevier, 2005 [2] Stish G Kndlikr, Zijie Lu, Therml Mngement Issues in PEMFC Stck- A brief review of current sttus, Applied therml Engineering 2009, 29: [3] BPM Rnjini, Ajit Kumr Kolr, A model for verticl plnr ir brething PEM fuel cell, J Power Sources 2007, 164: [4] KPAdzkp, JRmousse,YDube,HAkremi,KAgbossou,MDostie APoulin MFournier, Trnsient ir cooling therml modeling for PEM Fuel Cell, J Power Sources 2008, 179: [5] Young Hun Prk,Jerld A Kton, Development of PEM stck nd performnce nlysis including the effects of wter content in the membrne nd cooling method, J Power Sources 2008, 179: [6] Yuyo Shn, Song-Yul Choe, Seo-Ho Choi, Unstedy 2D PEM Fuel Cell modeling for stck emphsizing therml effects, J Power Sources 2007, 165: [7] Yi Zong, Bio Zhou,Andrzej Sobiesik, Wter nd Therml Mngement in single PEM Fuel Cell with nonuniform stck temperture, J Power Sources 2006, 161: [8] Tniguchi, Fuel Cell system, US Ptent , 2010 [9] Ishikw, Fuel Cell system hving cooling pprtus, US Ptent , 2002 [10] Cheng Bo, Minggo Ouyng, Bolin Yi, Anlysis of the wter nd therml mngement in proton exchnge membrne fuel cell systems, Int J Hydrogen Energy 2006, 31: [11] Sngseok Yu, Dohoy Jung, Therml Mngement strtegy for proton exchnge membrne fuel cell system with lrge ctive re, Renewble Energy 2008, 33: [12] SPndin, KJykumr, NRjlkshmi, KSDhththreyn, Therml nd electricl energy mngement in PEMFC stck-an nlyticl pproch, Int J Het Mss Trnsfer, 2008, 51: [13] Frnk P Incroper, Dvid P Dewitt, Fundementls of Het nd Mss trnsfer, Wiley,