Study the Effect of Using Offset Strip Fin Heat Exchanger on the Efficiency of Combined Gas Turbine with Air Bottom Cycle

Transcription

1 Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN Study th Effct of Using Offst Strip Fin Hat Exchangr on th Efficincy of Combind Gas Turbin with Air Bottom Cycl Rida Ali Hmouda and Hussain Alrubai Abstract Th main objctiv of this papr is to rsarch on th ffctivnss of th dvlopmnt of th industrial gas turbin, which works in from a simpl cycl to gas turbins stations that work in a Combind Joul/Joul Cycl (CJJC) (gas / air).this study utilizs th computation of th basic thrmal dsign of th simpl cycl gas turbins in ordr to idntify th conomical indicators for th thrmal procss of producing lctricity. Th computation rsults shows That th dprssion of th thrmal conomical indicators of ths stations (η S =36%) gav ris on both th tmpratur of th xhaust gass (T 4 =58.4 C) and Th quantity of th hat containd in th turbin s xhaust discardd in th atmosphr (.7MW). To solv ths ngativ problms of th basic thrmal dsign that would incras th quantity of th lctrical nrgy gnration and to sav th contamination at th lowr lvl. So in this papr th hat xchangr has bn dsignd, which has bn considrd an important lmnt in th procss of utilizing th thrmal nrgy of xhaust gass. Th study on th ffctivnss of th Combind Joul/Joul Cycl in industrial powr plants, Whr his study has bn dsignd Offst Strip-Fin hat xchangr has bn stablishd by using th mathmatical modl which was rsultd to a thrmal fficincy incras up to (η C =43.5%). Kywords Combind Joul/Joul Cycl, Gas turbin, Offst Strip-Fin hat xchangr. I. INTRODUCTION HE last dcad has witnssd rmarkabl improvmnts Tin industrial gas turbin siz and prformanc and th coming yars ar holding th promis of vn mor progrss in ths filds []. Du to vr incrasing costs of fossil fuls and awarnss of th impact on th nvironmnt of burning fossil fuls, it is sought to dcras fossil ful consumption. Various tchnological dvlopmnts ar mployd to lowr th ful consumption and mission of industrial gas turbin units, such as high tmpratur matrials and advancd combustion tchnologis. Howvr all of modrn gas turbin units oprat in a simpl cycl, i.., all th hat containd in th turbin s xhaust is discardd to th atmosphr. This lost Rida Ali Hmouda is with th Dpartmnt of Mchanical Enginring Univrsity of Misurata, ibya, (-mail: hmouda@yahoo.com). Hussain. Alrubai was with Collg of Enginring Tchnology Hoon, ibya. H is now with th Dpartmnt of Mchanical Enginring Univrsity of Baghdad, Iraq, (-mail: hussxycc@yahoo.com). hat rprsnts anywhr from 65-7 % of th ful nrgy, dpnding on th unit s thrmal fficincy. Convrting this rsidual hat into powr could provid in xcss of clan lctrical powr of much-ndd capacity to lctrical powr grid. Combind gas and stam turbins cycl looks lik logical approach in raising industrial plant fficincy, but this concpt is infficint in aras suffring from watr scarcity. Th Rcntly Propos a nw dsign for Combind cycl valid for us in industrial gas turbin. Joul Joul cycls can b combind by an air-gas Offst Strip Fin hat xchangr th xhaust of th primary gas turbin is snt to a hat xchangr, which, in turn, hats th air in th bottom cycl. Air is xpandd in th turbin to gnrat additional powr. In comparison to th Joul/Rankin combind cycl, this dsign dos not rquir bulky stam quipmnt (boilr, stam turbin, condnsr), or a watr procssing unit []. II. THE THERMA ANAYSIS OF THE SIMPE CYCE GAS TURBINE In prsnt study has bn using th following mthod to procdur thrmal analysis of gas turbin at dsign proprtis and oprating conditions for this unit, Whr this mthod rlis on procdur thrmal calculation of th basic parts of th gas turbin, in rlativ trms (pr kg of air th insid th comprssor). Also bn daling with th turbin blads cooling systm, as a sparat cycl to xtnd th cooling air insid th gas turbin [3]. A. Calculat Thrmal Economic Indicators for th Gas Turbin Simpl Cycl Air consumption rat of gas turbin (ton/hr), calculatd as: N GT G = 3600 () a H η η M G Whr N GT powr output (MW), H is th spcific work for gas turbin (kj/kg), η M is th mchanical fficincy and η G is th fficincy of th gnrator. Th Ful consumption rat of th gas turbin is calculatd as follows: BGT = G t G a () Whr G t is Th rlativ rat of ful consumption for th gas turbin (kg Ful/kg Air). 3

2 (MW) P (MW),,ar Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN Th thrmal Efficincy is calculatd as follows: GT N η = 3600 (3) S BGT Q Whr (QRCV R= kj/kg) hating valu for th ful usd. B. Combind Joul/Joul With Air Bottoming Cycl ik th stam bottoming cycl in a combind cycl, th air bottoming cycl (ABC) may utiliz hat rjctd from a gas turbin [4]. A gnral flow sht diagram of th CJJC is shown in Fig.. In th bottom cycl th ambint air () is drawn through a filtr and is comprssd in th air comprssor (AC). Th comprssd air (RAR) is hatd in Offst Strip-Fin hat xchangr bfor it ntrs (3RAR) air turbin. In th turbin th air is xpandd whil shaft work is gnratd. Aftr th turbin th air is xhaustd to a stack. Th work gnratd in th turbin is sufficint to driv th comprssor and a gnrator (G), (CC) dnots th combustion chambr and (GRCOR) Th rlativ amount of air drawn from th comprssor to cool th turbin blads [3]. N GT N AT G G Fig. Combind Joul/Joul with Air Bottoming Cycl. C. Calculat Thrmal Economic Indicators for th Combind Joul/Joul Cycl Th thrmal fficincy of th CJJC is calculatd as follows: 3600 N η C = (4) BGT Q CV Whr NRR th lctrical powr producd for CJJC and calculatd from th following rlationship: GT AT N = N + N (5) AT Exhaust Gas Air AC AC Whr NRRP th lctrical powr producd for ABC and calculatd from th following rlationship: AT HA η M ηg Ga N = (6) 3600 CV BGT CC 3 5 Gco Hat Exchangr A 3 A Air out GT AT 4 4 A Whr HRAR is th spcific work for ABC (kj/kg). III. THE OFFSET STRIP FIN HEAT EXCHANGER In this papr th hat xchangr has bn dsignd, which is considrd an important lmnt in th procss of xploitation of thrmal nrgy of th xhaust gass, whr has bn studid and dsignd cross flow hat xchangr from typ of plat fin. Th plat fin hat xchangr (PFHE) ar a form of compact hat xchangr consisting of a stack of altrnat flat plats calld parting shts and fin, brazd togthr as a block. Plat fin hat xchangr ar widly usd in various industrial applications bcaus of thir compactnss. For many yars, PFHEs hav bn widly usd for gas sparation in cryognic applications and for aircraft cooling dutis. In arospac applications wight saving is of paramount importanc [5]. Salint faturs of PFHE ar discussd by Shah and includ th following [6],[7]:. Plat fin surfac ar commonly usd in gas-to-gas xchangr applications.. Th passag hight on ach sid could b asily varid. 3. Th maximum oprating tmpraturs ar limitd by th typ of fin-to-plat bonding and th matrials mployd. PFHE hav bn dsignd from cryognic oprating tmpraturs to about 800P PC. Th hat of th gas turbin xhaust is rcovrd and transfrrd to th comprssd air btwn th comprssor and turbin of th ABC. For this application thr ar two diffrnt typs of hat xchangr that can b usd: rgnrators and rcuprators. In a rcuprator, hat is transfrrd through walls that sparat th flows. In a rgnrator, th hat transfr surfac is altrnatly xposd to th two flows [4]. In th prsnt work it was chosn a rcuprator bcaus of th following advantags [8].. Eas of manufactur.. Stationary natur. 3. Uniform tmpratur distribution and hnc lss thrmal shock. 4. Absnc of saling problm. Thr ar many forms of fins that can b usd with PFHE including offst strip, plain triangular, plain rctangular, wavy, louvr, prforatd, or pin fin gomtris. In this papr has bn study offst strip fin typ. Th offst strip fin (OSF) is commonly usd gomtry in PFHE. Th OSF is dsignatd as th srratd fin [5]. Th fin has a rctangular cross sction; it is cut into small strips of lngth RfR and vry altrnat strip is offst by about 50% of th fin pitch in th transvrs dirction as schmatically shown in Fig.. Fin spacing SS, fin hight H, fin thicknss δrfr, and strip lngth in th flow dirction RfR th major variabls of OSF fins. OSF gomtry is charactrizd by high hat transfr ara pr unit volum, and high hat transfr cofficints. Th hat transfr mchanism in OSFs is dscribd by Joshi and Wbb [9]. And is as follows. Th hat transfr nhancmnt is obtaind by priodic growth of laminar boundary layrs on th 4

3 Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN fin lngth, and thir dissipation in th fin waks. This nhancmnt is accompanid by an incras in prssur drop th thrmal nrgy rquird, so This problm was solvd for th mthod of studying anothr altrnativ. Th scond altrnativ: a study and dsign cross flow hat xchangr with thr passs. And so with th aim of incrasing th valu of log man tmpratur diffrnc (MTD). But th problm hr is difficulty in obtaining an quation or a chart to calculat th log man tmpratur diffrnc for th hat xchangr. Whr th typ of flow is a cross flow xchangr whit thr passs for ach stram and both strams unmixd. To solv this problm w divid th hat xchangr into thr xchangrs, ach of which rprsnts a pass intrscts it th hot and cold fluid prpndicular as shown in Fig. 4. T CO Fig.. Gomtrical dscription to OSFs cor a hat xchangr. bcaus of incrasd friction factor. A form drag forc, du to th finit thicknss of th fins, also contributs to th prssur drop. Fluid intrchang btwn channls is possibl. OSFs ar usd in th approximat Rynolds numbr rang of 500-0,000 [0]. Salint faturs prtaining to thrmal prformanc includ th following [5].. Commonly usd in air sparation plants whr high thrmal ffctivnss at low mass vlocitis is rquird.. Th hat transfr prformanc of OSFs is incrasd by a factor of about.5 to 4 ovr plain fins of similar gomtry [0]. 3. At high Rynolds numbrs, th J factor dcrass, whil th friction factor rmains constant bcaus of th high form drag. Thrfor OSFs ar usd lss frquntly for vry high Rynolds numbr applications. 4. Thy ar usd at low Rynolds numbr applications calling for accurat prformanc prdictions, such as som arospac applications. A. Th Analysis Mthod of Hat Exchangr Is known as that both of hot and cold fluids it flows during cross flow hat xchangr and both strams unmixd. In this study diffrnt altrnativs hav bn proposd for th dsign of th hat xchangr and th slction of a suitabl altrnativ btwn ths altrnativs, which ar as follows: Th first altrnativ: a study and dsign cross flow hat xchangr with singl pass for ach stram as shown in Fig. 3. T HI T CI Hat Exchangr T CO Fig. 3. Th hat xchangr with a singl pass. Whr it was found by th initial rsults of study that this altrnativ nds to arg of hat xchang ara in ordr to gt T H Fig. 4. Th hat xchangr with thr passs. B. Th Thrmal Analysis of th hat xchangr Th purpos of thrmal analysis of th hat xchangr is to dtrmin th rlationships for calculating ovrall hat transfr cofficint a hat xchangr and th xprssion of th thrmal nrgy that has Transfrrd from th hot to th cold fluids, dpnding on th surfac ara of th hat xchangr, and th log man tmpratur diffrnc. So this purpos can b achivd by thrmal nrgy balanc quation f or both hot (xhaust gass)and cold (air) fluids. Th og man tmpratur diffrnc (K) is calculatd as follows []: T m = T HI n T HO T CO 0.8 P A z ( T HI T CI ).8 0. R S 0. R S + n( P R) T min P = T HI T CI Hat Exchangr - 3 Hat Exchangr - T CI, Hat Exchangr - W min A z =, Wmax R = A z Whr T H (K) th xhaust gass tmpratur, T C (K) th air tmpratur, th indx I, O dnots inlt and outlt rspctivly, W min, max (kw/k) minimum and maximum hat capacity rat rspctivly, S, dimnsionlss factor and rprsnts th numbr of hat transfr units, and is calculatd from th following quation: ER xp[(xp( S A z ) ) R S ] T HO3 T CO T HO (7) = (8) 5

4 hight hat hat fin fin pitch numbr numbr wall Prandtl Prandtl thrmal Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN Whr ER Effctivnss of th hat xchangr. From th gomtrical dtails shown in Fig.. Can w gt th fr flow aras for xhaust gass and air as []: Calculat th fr flow ara for xhaust gass (mp P) as: δ (9) Aff H = ( H H F )( N H δ F ) H NP H NF H N H =, H NF H = Whr HRHR of th fin (m), R NRH frquncy, fins pr mtr, R RH xchangr lngth (m), SRH Rpitch distribution fins in th layr that passs through it xhaust gass, R NFRH of fins in th layr that passs through it xhaust gass. H S H Calculat th fr flow ara for air (mp P) as: Aff C = ( H C F )( N C δ F ) C NP C NF C N C =, C δ (0) NF C = Whr HRC Rhight of th fin (m), R NRC frquncy, fins pr mtr, R RC xchangr lngth (m), SRCR distribution fins in th layr that passs through it air, R NFRC of fins in th layr that passs through it air. Th hat transfr aras (mp P) for th xhaust gass can b obtaind as givn blow: AH C S C H C NP H [ + N H ( H H δ F )] = () Whr NPRH Rnumbr of layrs that passs through it xhaust gass. Similarly hat transfr aras (mp P) for th air can b obtaind as givn blow: AC H C NP C [ + N C ( H C δ F )] = () Whr NPRC Rnumbr of layrs that passs through it air. Th hat transfr ara through th wall btwn th layrs of th hat xchangr is calculatd from th following rlation: A = (3) W H C NP H Equivalnt hydraulic diamtr of th hat xchangr is calculatd as follows [9]: Equivalnt hydraulic diamtr (m) of th finnd passags for xhaust gass and air is givn by: ( SS H δ F )( H H δ F ) Dh H = ( H H δ F ) δ F [ SS H + ( H H δ F )] + f ( SS C δ F )( H C δ F ) Dh C = ( H C δ F ) δ F [ SS C + ( H C δ F )] + f Whr: SS H = δ, F N H SSC = δ F N C (4) (5) Th ovrall hat transfr cofficint through th hat xchangr is calculatd as following []: Th hat transfr cofficint (W/mP P.K) for xhaust gass can b obtaind in trms of Colburn J factor as following : J H G H C PH α H = Aff ( Pr ) 3 H fh (6) Whr Colburn (JRHR) factor for th xhaust gass is calculatd as follows [9]: 0.4 f 0.4 δ F 0.0 J H = 0.( R fh ) ( ) ( ) Dh H Dh H Whr PrRfh R numbr, RRfhR Rynolds numbr. (7) Th hat transfr cofficint (W/mP P.K) for air can b obtaind in trms of Colburn J factor as following : J C G C C PC α C = Aff ( Pr ) 3 C fc Whr Colburn (JRCR) factor for th air is calculatd as [9]: 0.4 f 0.4 δ F J C = 0.( R fc ) ( ) ( Dh C Dh C Whr PrRfc R 0.0 ) numbr, RRfcR Rynolds numbr. Thus, th ovrall hat transfr cofficint is calculatd as: = + δw + UA α H A H λw A W αc A C Whr δrwr thicknss (m), R λrw conductivity of th wall mtal (W/m.K). Th thrmal nrgy (kw) xchangd within th hat xchangr is calculatd from th following rlation: Q UA T m (8) (9) (0) = () Th prssur loss cofficint from xhaust gass sid is calculatd as follows: P TH ζ H = ζ = Gas P H PTH = P FH + P CH () (3) Prssur drop (Pa) during passags for xhaust gass is calculatd as [9]: H U 4 f H C ρ FH P FH = Dh H 0.36 f 0.65 δ F 0.7 f H =.( R fh ) ( ) ( ) Dh H Dh H PCH = 0.5( ρ HO U HO ρ HI U HI ) (4) (5) (6) Th prssur loss cofficint from air sid is calculatd as: 6

5 , dnsity or or Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN P TC ζ C = ζ = Air P C PTC = P FC + P CC (7) (8) Prssur drop during passags for air is calculatd as [9]: C U 4 f C H ρ FC P FC = Dh C 0.36 f 0.65 δ F f C =.( R fc ) ( ) ( Dh C Dh C PCC = 0.5( ρco U CO ρci UCI ) 0.7 ) (9) (30) (3) 3 Whr ρrhr ρrcr of th fluid (kg/mp P) at th man tmpratur of both gass and air rspctivly, ρrhir, ρrhor, ρrcir, ρrcor, dnsity th ntry and xit of gass and air to th hat xchangr rspctivly, URFH R, URFCR vlocity in narrowst cross sction for both gass and air (m/s), URHI R, URHOR, URCI R, URCOR vlocity th ntry and xit of gass and air to th hat xchangr rspctivly, PRHR PR4 R(Pa) gas prssur, PRCR PRA R(Pa) air Prssur, ΔPRCHR, ΔPRCC R(Pa) Prssur drop du to Chang in vlocity for gass and air rspctivly. IV. RESUTS AND DISCUSSION From th mathmatical modl of ssntial dsign for simpl cycl gas turbin, has bn studid th ffct of turbin inlt tmpratur (TIT), and th impact of th prssur ratio in th comprssor (PRRCR) on ach of th thrmal fficincy and spcific work. Fig. 5. Shows that incrasing th TIT lads to an incras in th thrmal fficincy of th cycl du to incrasd spcific work and incras th lctrical powr producd that incras th thrmal fficincy of th cycl. W also not that incrasing th PRRCR incrass th thrmal fficincy. Whr du to Incrasing th PRRCR ads to rais th tmpratur of th air that coms out of th comprssor, and thus rduc th ful consumption and incras th thrmal fficincy of th cycl. Whr it is notd that th fficincy up to (ηrsr=36.06%) whn (TIT=00 C, PRRCR=5). Thrmal Efficincy (%) ηs(tit=000 C) ηs(tit=00 C) ηs(tit=00 C) H(TIT=000 C) H(TIT=00 C) Prssur Ratio Fig. 5. Efficincy and spcific work as function of comprssor prssur ratio. Also has bn usd mathmatical modl for ABC to study th ffct of th ffctivnss of th hat xchangr, as wll as Spcific Work (kj/kg) study th ffct of th prssur ratio in th bottoming cycl (PRRCAR) on thrmal fficincy of th combind cycl. Fig. 6. Shows that incras th ffctivnss of th hat xchangr lads to incrass th fficincy of th cycl. And th rason for this is that th incrasd ffctivnss of th hat xchangr lads to rais th tmpratur of th air that coms out of th hat xchangr, and thrby incras both of spcific work and th lctrical powr producd for ABC, Which in turn contributs to incras th thrmal fficincy of th combind cycl. It also nots from th Fig. 6. That incrasing th PRRCAR lads to incrasing th thrmal fficincy of th cycl du to incrasd spcific work. Aftr that with th incras in th PRRCAR, w not a dcras in thrmal fficincy du to rais th tmpratur of th air that coms out of th comprssor. Th rason for this is du to th dcras air dnsity and incrasd its vlocity, lading to incras th prssur loss from th air sid of th hat xchangr. Thrmal Efficincy (%) ηc(er=75%) ηc(er=8%) ηc(er=80%) ηc(er=85%) TIT=00 C PRC= Prssur Ratio for Bottoming Cycl Fig. 6. Optimization of th ovrall prssur ratio in ABC. Fig. 6. Also shows th optimum valu of th prssur ratio for bottom cycl, which givs th highst fficincy for th combind cycl as is clar from th Fig. 6. that this valu is (PRRCAR=4.5) at all th valus of th hat xchangr ffctivnss. As can b sn from th Fig. 6. That valus fficincy droppd at (PRRCAR>4.5, ER=85%) du to th dclin in th valu of th log man tmpratur diffrnc of th hat xchangr. Th maximum valu of th fficincy hav bn achivd at (ηrcr=43.5 %,TIT=00 C, PRRCR=5, ER=85%). Fig. 7. Shows th ffct of th ffctivnss of th hat xchangr on both thrmal fficincy and spcific work for topping gas turbin cycl, as is clar from th Fig. 7. That th highst valu for th fficincy of th cycl b at (ηrcr=43.5%, ER=85%), whil th highst valu for th spcific work b at (H=36.4 kj/kg, ER=85%). As can b sn from th Fig. 7. Also incras th ffctivnss of th hat xchangr lads to incrasd spcific work, du to incrasing th numbr of layrs that passs through it both of xhaust gass and air in th hat xchangr. This in turn lads to a drop in th vlocitis of ach of th xhaust gass and th air passing through ths layrs, and thus lowr of th losss in th prssur from sid of th 7

6 Intrnational Journal of Mining, Mtallurgy & Mchanical Enginring (IJMMME) Volum, Issu 3 (03) ISSN ; EISSN xhaust gass and from sid of th air in th hat xchangr, and thus incras th spcific work for th cycl. Thrmal Efficincy (%) 36.4 Fig. 7. Efficincy and spcific work as function of Effctivnss of OSF hat xchangr. Also has bn studid th ffct of ffctivnss of th hat xchangr on th siz of th hat xchangr usd. Fig. 8. Shows that incrasing th ffctivnss of th hat xchangr lads to incras th siz of th hat xchangr. Siz ( m³ ) Fig. 8. Th siz at diffrnt valus of Effctivnss. Also has bn studid th ffct of turbin inlt tmpratur TIT on th thrmal fficincy for th combind cycl and simpl cycl at diffrnt prssur ratios as shown in Fig. 9. Whr nots that by incrasing th TIT, lads to incrass thrmal fficincy for both simpl cycl and combind cycl, also nots that incrasing th prssur ratio incrass th thrmal fficincy of simpl cycl and combind cycl. Thrmal Efficincy (%) Efficincy (%) Spcific Work TIT=00 C PRC=5 PRCA=4.5 ER=80% ER=8% ER=85% Effctivnss of Hat Exchangr TIT=00 C PRC=5 PRCA=4.5 80% 8% 85% Effctivnss of Hat Exchangr Effctivnss =85% Prssur Ratio ηs(tit=000 C) ηs(tit=00 C) ηs(tit=00 C) ηc(tit=000 C) ηc(tit=00 C) ηc(tit=00 C) Spcific Work (kj/kg) V. CONCUSIONS Th conclusion is that th convrt industrial gas turbins into combind Jul/Jul cycl is an conomical altrnativ for powr gnration. Th prssur ratio was found optimal at 5 in topping cycl and 4.5 in bottoming cycl. A rcuprator is rcommndd instad of a rgnrator for th hat transfr from th gas turbin xhaust gas to th comprssd air of th ABC. Th combind Joul/Joul cycl fficincy was calculatd to 43.5 prcnt. Th simpl cycl gas turbin fficincy was calculatd to 36 prcnt thus Implmntation of th air bottoming cycl at a gas turbin adds 7.5 prcnt points to th simpl cycl fficincy, and a ris in th powr output of 0.5 to 3 prcnt dpnding on th comprssion ratio. Whn compard with th stam bottoming cycl, th ABC showd prformanc valus clos to and xcding thos of th stam bottoming cycl, whil faturing a simplr and robust dsign, smallr dimnsions, this combind systm is vry much lss costly than that using stam by dispnsing with boilr, stam turbin, condnsr, pumps, watr tratmnt plant, cooling towrs, tc. ACKNOWEDGMENT To th Univrsity of Misurata to support this work. REFERENCES [] P. J. Dchamps, Advancd Combind Cycl Altrnativs With th atst Gas Turbins J. Eng. Gas Turbins Powr 0(), , Apr 0, 998. [] R. A. Hmouda, Study Th Effctivnss of using Combind Joul/Joul Cycl in industrial powr plants for ibyan oil and gas filds, MSc Thsis. Faculty of Enginring, Misurata Univrsity, ibya 009. [3] I. V. Arsynv, and V. B. Tyryshkin, Gas Turbin Powr Plants ningrad, Moshinostroin, pp. 543, 989. [4] O. Bolland, M. Ford, and B. Hand, Air Bottoming Cycl: Us of Gas Turbin Wast Hat for Powr Gnration, ASME Papr 95- CTP-50, 995. [5] M. A. Taylor, d. Plat-fin hat xchangrs, guid to thir spcification and us, HTFS (Harwll aboratory), Oxon, UK, 980. [6] R. K. Shah, Compact hat xchangr for th procss industry, in Enrgy Efficincy in Procss Tchnology, (P. A. Pilavachi, d.), Elsvir Applid Scinc, ondon, pp [7] R. K. Shah, Compact hat xchangr tchnology, and applications, in Hat Exchang Enginring, Vol., Compact hat xchangr: Tchniqus of Siz Rduction (E. A. Foumny and P. J. Hggs, ds.), Ellis Horwood, Nw York, 99, pp. -9. [8] T. Kuppan, Hat Exchangr Dsign Handbook, CRC Prss, pp , 306, 000. [9] H. M. Joshi, and R.. Wbb, Hat Transfr and Friction in th Offst Strip-Fin Hat Exchangr Intrnational Journal of Hat and Mass Transfr, Vol. 30, pp , 987. [0] R. K. Shah, Compact hat xchangr surfac slction, optimization, and comutr aidd thrmal dsign, in ow Rynolds Numbr Flow Hat Exchangrs (S. Kakac, R. K. Shah, and A. E. Brgls, ds.), Hmisphr, Washington, D. C., 983, pp [] P. E. Bajan, and G. E. Kanvts, Hat Exchangrs Moscow-Ussr, Mashinostrain Prss, pp. 365, 989. [] M. Mishar, P. K. Das, and S. Sarangi, Optimum Dsign of Cross Flow Plat-Fin Hat Exchangrs Through Gntic Algorithm Intrnational Journal of Hat Exchangrs, Vol. 5, pp , 004. Fig. 9. Comparison btwn fficincy of simpl and combind cycl. 8