International Journal of Engineering Research & Technology (IJERT) ISSN: Vol. 2 Issue 7, July

Transcription

1 Mathmatical Modlling Of A Plat Typ Hat Exchangr For A 0.1 MW OTEC Plant Vijayakrishna Rapaka E*, Michal Bakkiyanathan D** *Formr Assistant Profssor, Dpartmnt of Mchanical Enginring, Pondichrry Enginring Collg, Puduchrry India **Formr PG Studnt, Dpartmnt of Mchanical Enginring, Pondichrry Enginring Collg, Puduchrry India Abstract Th sarch for rnwabl sourcs of nrgy rsultd in th rvival of a concpt Ocan Thrmal Enrgy Convrsion which utilizs th diffrnc in tmpratur btwn th warm tropical surfac watrs and th cold dp ocan watr availabl at dpths of about oprating in a Rankin cycl. Th hat xchangrs ar th major componnts of th OTEC powr plants and thy play an important rol in th conomy of th OTEC powr plants, hnc a propr slction of matrials, dsign critria, working fluid and working conditions for th hat xchangrs ar ncssary for an nrgy fficint and tchno-conomically fasibl OTEC powr plant. Th following paramtrs: pip lngth, pip diamtr, sawatr dpth and th flow rat of sawatr wr considrd. Th thortical invstigations rvald that a maximum output of th nt work xists at a crtain flow rat of cooling sawatr. In this rport, th dsign of hat xchangr for a 0.1 MW OTEC powr plant is carrid out and th prformanc of th hat xchangr for varying dpths, for varying vlocitis of th intak fluid, for varying mass fraction of th working fluid, for varying lngth of th plats is simulatd using Enginring Equations Solvr. In addition, th variation in th Rynolds numbr, Nusslt numbr, Prssur drop and Ovrall hat transfr cofficint for varid procss conditions ar stimatd and prsntd in graphical form. 1. Introduction Th ocan thrmal nrgy concpt was proposd as arly as 1881 by th Frnch physicist Jacqus d Arsonoval. This is an indirct form of collction and storag of solar nrgy. Th surfac of th watr acts as th hug collctor for solar hat thrby acting as an infinit hat storag rsrvoir. Th hat thus collctd in th ocans can b convrtd into lctricity by utilizing th tmpratur diffrnc btwn th warm surfac watr of th tropical ocans and th coldr watrs in th dpths which is about 0 5 K using a rankin cycl. Th abov concpt of utilization of this tmpratur diffrnc in a hat ngin to gnrat powr is calld ocan thrmal nrgy convrsion (OTEC). Th amount of nrgy availabl for th ocan thrmal powr gnration is normous, and is rplnishd continuously. Th surfac tmpratur dpnds on th latitud and sason. Basd on th latitud and sason, it is vidnt that th surfac watr tmpraturs ar maximum in th tropical, sub-tropical, and quatorial watrs i.., btwn th tropics, making ths watrs th most suitabl for OTEC systms. Thr ar two diffrnt mthods for harnssing ocan thrmal diffrncs. On is th Opn cycl, also known as th Claud cycl, and othr is th closd cycl systm, also known as th Andrson cycl Opn cycl OTEC systm Th Claud cycl or opn cycl utilizs th vapor prssur of sa watr itslf as th working mdium and has bn dmonstratd to b practicabl. Opn cycl rfrs to th utilization of sa watr by flash vaporating th working fluid undr partial vacuum conditions. Th low prssur stam thus obtaind is passd through a turbin for xtracting nrgy and th spnt vapor is coold in a condnsr. This cycl drivs th nam opn form th fact that th condnsat is nvr rturnd to th vaporator instad th condnsat is utilizd as dsalinatd watr using a surfac condnsr or a spray (dirct-contact) condnsr. Vry larg ocan watr and volum flow rats ar usd in th opn OTEC systms and th turbin oprating at a vry low prssur rciv rquirs spcific volums mor than 000 tims in comparison to th spcific volum rquirmnt in a modrn fossil ful powr plant. Du to th high spcific volums xtrmly larg turbins must b usd. In addition, dgasifirs ar ssntial to rmov th gass dissolvd in th sa watr. 991

2 Figur 1. Opn cycl OTEC systm 1.. Closd cycl OTEC systm Th closd cycl was first proposd by Barjot in 196, but th most rcnt dsign was by Andrson in In this cycl, propan or ammonia can b usd as a working fluid. Th tmpratur diffrnc btwn warm surfac and cold watr from th dp is 0 C. Th cold watr is pumpd from a dpth of. Th working fluid is vaporizd in th boilr (vaporator) at 10 bar and xhaustd in th condnsr at 5 bar. Th high prssur vapor laving th vaporator ntrs an xpansion turbin thrby producing usful nrgy. Th usful mchanical nrgy from th turbin is convrtd to lctrical nrgy using and an lctric gnrator. Th low prssur xhaust from th turbin is coold and convrtd back into liquid in th condnsr. Th cooling is achivd by passing cold, dp ocan watr, from a dpth of 700 to 900m or mor, through a hat xchangr. Th liquid working fluid is thn pumpd back as high prssur liquid to th vaporator, thus closing th cycl. Figur. Closd cycl OTEC systm. Litratur Survy Mitsutru, K., and Ikgami,Y., [[8]] hav carrid out th prformanc valuation of th ovrall hat transfr cofficint and boiling hat transfr cofficints of a plat typ vaporator using ammonia/ watr mixturs. Uhara, H., and Ikgami, Y., [[16]] hav carrid out study on th Optimization of an OTEC powr plant with plat typ hat xchangrs and concludd that th plat hat xchangrs produc bttr hat transfr rats whn compard to th shll and tub hat xchangrs. Uhara, H., t al [[17]] carrid out studis on th prformanc of an OTEC powr plant with ammonia and watr as working fluid and concludd that th prformanc of th plant incrass whn compard to othr combinations with fwr factors of safty. Tsutomo Nakaoa and Uhara [[15]] hav carrid out xprimnts with Shll and Plat Hat xchangrs (vaporator) and with Fron1 and hav found that th Ovrall hat transfr cofficint incrass. Paras, S.V. t al [[1]] hav studid th various diamtrs of th tubs usd for th hat transfr in th plat typ hat xchangr and th flooding ffct that taks plac in th small diamtr tubs in th cas of vrtical tubs and th ffct of th inclination angl in th plat typ hat xchangrs. Paras, S.V. t al [[11]] hav studid th ffct of groovs in th plat typ xchangr. Th channl usd for th simulation is formd by only on corrugatd plat, and two sid-groovs, whil th othr plat is flat. Th various Rynolds numbrs usd hav bn ranging form A standard k-ε modl was usd for th calculations and, in addition to isothrmal flow, hat transfr simulations wr carrid out for th cas of hot air. Fock t al [[3]] hav studid th prformanc of th plat typ hat xchangr with various angls of inclination and also th ffct of flow and hat transfr proprtis for a givn hydraulic diamtr of th hat xchangr. Hsslgravs, J. E., [[6]] has studid and formulatd som dsign critria and som oprating conditions for th compact typ hat xchangrs and also th prformanc charactristics of ths hat xchangrs. Wongwiss, S., [[18]] has studid th ffct of th inclination angl in th straight pips and has compard th rsults with that of th vrtical pips and uppr nd conditions on th countrcurrnt flow limitation in straight circular pips. Mitsumri t al [[14]] hav carrid out prformanc studis of a plat typ hat xchangr by comparing it with a doubl-flutd tub typ xchangr. Thy hav fond that th plat typ hat xchangr offrs mor prformanc than th tub typ hat xchangr. Blomrius, H and Mitra, N.K., [[1]] hav mad numrical invstigation on th hat transfr and prssur drop in wary ducts and hav found that th prssur drop incrass varis with th duct diamtr and th convctiv hat transfr also incrass. Fock, W and Knibb, P.G., [[]] hav carrid out CFD analyss on th flow of th fluid insid th paralllplats ducts with corrugatd wall and hav found that th inclination angl or th chvron angl plays an important rol in th fficint prformanc of th paralll plat ducts. Furthr th fficincy of th ducts is incrasd by th us of corrugatd walls as mor surfac hat transfr is obtaind. Sriyutha Murthy, P t al [[10]] hav suggstd Bio-film control for th plat hat xchangrs using surfac 99

3 sawatr from th for a OTEC powr plant for th fficint rduction of th fouling in th hat xchangr which is th major disadvantag has th plat typ hat xchangr must b covrd with thin films for th plats to b hld in a tight mannr. Alln, H.G., and Karayiannis, T.G., [[9]] hav considrd th cas for using lctro hydrodynamic (EHD) nhancmnt of hat transfr in thrmodynamic rnwabl nrgy applications whr tmpratur lvls ar rlativly low. Thy also stablishd th basis on which nuclat boiling hat transfr is nhancd by EHD forcs at surfacs dsignd to improv condnsation, giving xprimntal rsults for a six-tub, shll/tub hat xchangr for boiling R1. Havnr, R.L., t al [[4]] hav studid th prformanc charactristics of a plat typ hat xchangr which is usd for industrial purpos and th ffct of th chvron angl on th prformanc charactristics of th hat xchangr. Hggs, P.J., t al [[5]] has invstigatd th ffct of th local transfr cofficints which plays a major rol in th fficint and tchnoconomically dsign of a hat xchangr. It is found that th local hat transfr incrass. Kays, W.M. and London, A.L., [[7]] hav mad xtnsiv rsarch on th compact typ hat xchangrs. Thy hav studid th ffct of fins in incrasing th ffctivnss of th hat xchangrs and hav obtaind various rsults on th ffct of fins on th dsign paramtrs of a compact typ hat xchangr. Shah, R.K. and Wanniarachi, A.S., [[13]] hav proposd th dsign procdurs for a plat typ hat xchangr usd for industrial purposs. 3. Hat Exchangrs Hat xchangrs ar dvics usd for transfr of hat from on flowing fluid to anothr through a solid barrir sparating ths fluids. Thr ar various typs of hat xchangrs usd for th purpos of hat xchang btwn two fluids. Hat xchangrs ar basically classifid according to flow arrangmnt and typ of construction. Th following ar th typs of hat xchangrs most commonly usd in th industrial applications Doubl pip hat xchangr Th simplst hat xchangr is on for which th hot and cold fluids mov in sam or opposit dirction in a concntric tub which is othrwis calld as th doubl pip hat xchangr. Th two typs of flow arrangmnt in th doubl pip hat xchangr is th Paralll and Countrflow arrangmnt. In th paralll flow arrangmnt th hot and cold fluids ntr at th sam nd, flow in th sam dirction, and both th fluids xits at th opposit nd. In th countrflow arrangmnt th fluids ntr at th opposit nds, flow in th rvrs dirctions rlativ to ach othr dirction and lav at opposit nds. Figur 3. Doubl pip hat xchangr 3.. Shll and Tub hat xchangr Anothr common configuration of hat xchangr is th Shll and Tub typ hat xchangrs. This typ of hat xchangr is widly usd in th chmical procss industris. In this typ on fluid flows on th insid of th tubs whil th othr fluid is forcd through th shll and ovr th surfac of th tubs. To nsur that th shll sid fluid will flow across th tubs uniformly in ordr to induc highr hat transfr, baffls ar placd in th shll at pr-dtrmind locations. Dpnding on th had arrangmnt at th nds of th hat xchangr, on or mor tub passs can b providd. Figur 4. Shll and tub hat xchangr In this xchangr th gas flowing across th tubs is mixd stram, whil th fluid in th tubs is unmixd. Th gas shows a mixd flow bhavior as it is allowd to mov about frly in th xchangr as it xchangs hat. Th unmixd fluid is confind in th sparat tubular channls in th hat xchangr thrby prvnting th fluid to gt mixd during th hat transfr procss Plat Typ Hat xchangrs: Th plats which ar th main componnts of th plat hat xchangr ar attachd togthr in a larg fram with rubbr gaskts that ar placd btwn ach plat. Thr ar four flow ports on ach plat. Th gaskt blocks on top and on bottom port so that th fluid flows by th rmaining two opn ports. This will b rvrsd for th nxt plat countrcurrntwis. This arrangmnt improvs considrably th hat transfr btwn 993

4 th two fluids and nsurs non mixing of th flowing fluids. Figur 5. Plat typ hat xchangr Prandtl numbr Vlocity of th fluid Mass flow rat m a u 4 m = m = kg / s q mcp T.0000 m/ s q q 4.13 kj / kgk Dimnsionlss numbr Advantags of plat hat xchangrs ovr shll and tub hat xchangrs - High ovrall hat transfr cofficint - Low cost - Lowr spac rquirmnt - Easy maintnanc - Lss wight - Lowr hat loss Howvr, thy also hav a fw disadvantags such as bing not suitabl for tmpraturs highr than 00 C and prssurs highr than 0 bar. Additionally, th fluids must hav a maximum viscosity of 10 Pa. s. Sinc th tmpratur handld in warm watr is around 5 30 C and prssur around 10 bar, th plat typ hat xchangr can b usd for OTEC powr plants. 4. Dsign of plat typ hat xchangr) Plat lngth m Plat width 0.13 m Man spacing btwn plats, b 0.04 m Corrugation angl / Chvron Angl 60 Port-to-port lngth 0.35 m Plat width insid gaskt, w m No. of Plats 100 Outr Diamtr of th tub 13*10-3 m Innr Diamtr of th tub 7*10 - m 4.1. Hot fluid sid (T h = 88 K) Avrag Tmpraturs for hot fluid sid T avg = 88 K Tabl 1. Fluid proprtis for th avrag tmpratur (88 K) Paramtrs Hot Fluid Units Dnsity kg / m Spcific hat kj / kgk Thrmal conductivity Viscosity / W / mk 3 kg ms Rynolds numbr u D R D Width of th corrugatd plat D 0.01 D 0.0 m R R 14 Nusslt Numbr Nu 0.8 R Pr Nu Nu Hat transfr cofficint h D Nu k Nu k h D h 0.01 h W / mk Numbr of transfr units T NTU LMTD T LMTD NTU 88 LMTD LMTD 144 C 994

5 Dsign ovrall hat transfr cofficint U Q LMTD A U U W / m K U KW / m K Mass vlocity m Gm N wd p Gm Gm kg / m s Prssur drop f Gm L P g D N p N p N N p f f P P 3775 Pa P kpa 4.. Cold fluid sid (T c = 79 K) Avrag Tmpraturs for hot fluid sid T avg = 79 K Tabl. Fluid proprtis for th avrag tmpratur (79 K) Paramtrs Cold Fluid Units Dnsity kg / m Spcific hat kj / kgk Thrmal conductivity Viscosity / W / mk kg ms Prandtl numbr Dimnsionlss 3 Vlocity of th fluid Mass flow rat m a u 4 m = m = kg / s q mcp T q q kj / kgk numbr.0000 m/ s Rynolds numbr u D R D Width of th corrugatd plat D 0.01 D 0.0 m R R 34.5 Nusslt numbr Nu 0.8 R Pr Nu Nu Hat transfr cofficint h D Nu k Nu k h D h 0.01 h 31.3 W / mk Numbr of transfr units T NTU LMTD T LMTD NTU 79 LMTD LMTD C 995

6 Dsign ovrall hat transfr cofficint U Q LMTD A U U 4510 W / m K U 4.51 KW / m K No. of passs, N p 50 Mass vlocity m Gm N wd p Gm Gm 1550 kg / m s Prssur drop f Gm L P g D N p N p N N p f f P P 9140 Pa P kpa Gomtric charactristics of th corrugatd Plat typ hat xchangr Plat lngth m Plat width 0.13 m Man spacing btwn plats, b 0.04 m Corrugation angl / Chvron Angl 60 Port-to-port lngth 0.35 m Plat width insid gaskt, w m Man flow cross-sction channl ara, A f 3.88*10-4 m Hat transfr ara, A.51*10 - m No. of Plats 100 Outr Diamtr of th tub 13*10-3 m Innr Diamtr of th tub 7*10 - m Equivalnt diamtr, D *10 - m Figur 6. Dsign drawing of th plat typ hat xchangr 5. Rsults and discussions Th various rsults obtaind during th dsign of th plat typ hat xchangr and th factors that influnc th dsign of hat xchangr and thir variations ar plottd in a graph. Th variation in th prssur drop, th variation in th ovrall hat transfr cofficint, th variation in th Rynolds numbr, th variation in th Nusslt numbr for both hot and cold fluid at diffrnt dpths for diffrnt lngths ar plottd. Th factors affcting ths paramtrs and th prcntag incras or dcras for ths paramtrs ar discussd. Furthr th vlocity which plays a major rol in th hat xchangrs has bn also discussd. Th variations that th vlocity causs on th prssur drop for both hot and cold fluid for diffrnt lngths of th pip at diffrnt dpths hav bn plottd. Th prcntag incras of th prssur drop for th variation in th vlocity intak at diffrnt dpths for varying lngth of th plat is rportd. Figur 7 shows th ffct of plat lngth on th prssur drop on th hot and th cold fluid sid for various dpths. Th prssur drop dcrass with th incras in th plat lngth. Th prssur dcrass bcaus for th sam vlocity as th lngth incrass th flow will b lss turbulnt thrby rducing th prssur drops. Th prcntag dcras in th prssur drop at dpths,,, and for th plat lngth from is 6.5%, 60%, 66%, 67%, 50%. Th prcntag dcras in th prssur drop at dpths,,, and for th plat lngth from is 996

7 (R) numbr on th hot fluid sid Hat transfr cofficint on th hot fluid sid (kw/k) Prssur drop (kpa) 8.5%, 75%, 60%, %, 87.55%. Th prcntag dcras in th prssur drop at dpths,,, and for th plat lngth from is 3%, 35%, 7%, 70%, 41.5%. Th prcntag dcras in th prssur drop at dpths,,, 900 m and for th plat lngth from is 0%, 8%, 6%, 35.63%, 39.3% numbr is around but th flooding in th us of small tub diamtrs is mor whn compard to th larg tub diamtrs. Th prcntag incras of (R) numbr at th dpths,, 800 m, and for a vlocity of -. is 9.09%, 8.%, 7.6%, 7.%, 7.05%. Th prcntag incras of (R) numbr at th dpths, 700 m,, and for a vlocity of. -.4 is 9.03%, 7.7%, 8.75%, 7.5%, 7.5%. Th prcntag incras of (R) numbr at th dpths,,, and for a vlocity of is 9.03%, 8.3%, 7.6%, 7.%, 7.16%. Th prcntag incras of (R) numbr at th dpths,,, and 1000 m for a vlocity of.6.8 is 9.13%, 8.3%, 7.6%, 7.13%, 7.5%. Th prcntag incras of (R) numbr at th dpths,,, and for a vlocity of.8 3 is 9.13%, 8.3%, 7.6%, 7.13%, 7.5% Plat lngth (m) Figur 7. Comparison btwn th plat lngth and prssur drop at diffrnt dpths Vlocity of th fluid (m/s) Figur 9 comparison btwn th plat lngth and hat transfr cofficint on th hot fluid sid at various dpths Vlocity of fluid (m/s) Figur 8. Comparison btwn th plat lngth and Rynolds numbr at diffrnt dpths Figur 8 shows th ffct of th vlocity of th fluid on th Rynolds numbr on th hot fluid sid for a plat lngth of 0.4 m at various dpths. Hr th lngth is kpt constant Th Rynolds numbr incrass with incrass in th vlocity bcaus of th linar rlationship. Th Rynolds numbr should as small as possibl in th corrugatd plat typ hat xchangrs in ordr to avoid th flooding in th tubs along with th intak vlocity of th fluid. Th rsarch work carrid out by Mouza t al [[19]] for th plat lngth of 0.4 m and with a tub diamtr of 7 mm shows that th Rynolds Figur 9 shows th ffct of th vlocity of th fluid on th hat transfr cofficint on th hot fluid sid for a plat lngth of 0.4 m at various dpths. Th hat transfr cofficint incrass as th vlocity of th fluid incrass. Th hat transfr cofficint incrass bcaus th nusslt numbr incrass. Th prcntag incras of hat transfr cofficint at th dpths,,, 900 m and for a vlocity of -. is 7.3%, 6.7%, 6.14%, 5.75%, 5.55%. Th prcntag incras of hat transfr cofficint at th dpths,,, and for a vlocity of. -.4 is 7.36%, 6.8%, 6.14%, 5.76%, 5.56%. Th prcntag incras of hat transfr cofficint at th dpths,,, 900 m and for a vlocity of is 7.38%, 6.1%, 6.7%, 6.13%, 5.8%. Th prcntag incras of (R) numbr at th dpths, 700 m,, and for a vlocity of.6.8 is 9.13%, 8.3%, 7.6%, 7.13%, 7.5%.Th prcntag incras of hat transfr cofficint at 997

8 Hat transfr cofficint on th cold fluid sid (kw/k) (Nu) numbr on th hot fluid sid th dpths,,, and 1000 m for a vlocity of.8-3 is 7.5%, 7%, 7.14%, 5.90%, 4.89% Vlocity of th fluid (m/s) Vlocity of th fluid (m/s) Figur 11. Comparison btwn th plat lngth and nusslt numbr on th hot fluid sid at various dpths Figur 10. Comparison btwn th plat lngth and hat transfr cofficint on th cold fluid sid at various dpths Figur 10 shows th ffct of th vlocity of th fluid on th hat transfr cofficint on th cold fluid sid for a plat lngth of 0.4 m at various dpths. Th hat transfr cofficint incrass as th vlocity of th fluid incrass. Th hat transfr cofficint incrass bcaus th nusslt numbr incrass. Th prcntag incras of hat transfr cofficint at th dpths,,, 900 m and for a vlocity of -. is 7.%, 6.3%, 5.1%, 6.9%, 7.11%. Th prcntag incras of hat transfr cofficint at th dpths,,, and for a vlocity of. -.4 is 7.1%, 6.4%, 5.5%, 6.95%, 6.0%. Th prcntag incras of hat transfr cofficint at th dpths,,, and 1000 m for a vlocity of is 7.%, 6.3%, 5.1%, 6.55%, 7%. Th prcntag incras of hat transfr cofficint at th dpths,, 800 m, and for a vlocity of is 7.3%, 6.7%, 5.13%, 6%, 6.66%. Th prcntag incras of hat transfr cofficint at th dpths,,, and for a vlocity of.8-3 is 7.%, 6.4%, 5.1%, 6.87%, 7%. Figur 11 shows th ffct of th vlocity of th fluid on th Nusslt numbr on th hot fluid sid for a Plat lngth of 0.4 m at various dpths. Th Nusslt numbr incrass as th vlocity of th fluid incrass. Furthr th nusslt numbr is th dimnsionlss numbr which mainly dpnds on th ffct of two othr dimnsionlss numbrs. As th Rynolds numbr and th Prandtl numbr incrass th Nusslt numbr also incrass. Th prcntag incras of Nusslt numbr at th dpths 600m, 700m, 800m, 900m and 1000m for a vlocity of -. is 7.9%, 6.7%, 4.5%, 4.67%, 5%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of. -.4 is 7.68%, 7.69%, 7.69%, 7%, 8%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of is 7.69%, 6.14%, 7.14%, 8.1%, 8%. Th prcntag incras of Nusslt numbr at th dpths,, 800 m, and for a vlocity of is 7.69%, 7.14%, 7.14%, 7.15%, 7.%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of.8-3 is 6.66%, 6.67%, 6.66%, 6.66%, 6.66%. 998

9 (Nu) numbr on th cold fluid sid Prssur drop on th hot fluid sid (kpa) Vlocity of th fluid (m/s) Vlocity of th fluid (m/s) Figur 1. Comparison btwn th plat lngth and nusslt numbr on th cold fluid sid at various dpths Figur 1 shows th ffct of th vlocity of th fluid on th Nusslt numbr on th cold fluid sid for a Plat lngth of 0.4 m at various dpths. Th Nusslt numbr incrass as th vlocity of th fluid incrass. Furthr th nusslt numbr is th dimnsionlss numbr which mainly dpnds on th ffct of two othr dimnsionlss numbrs. As th Rynolds numbr and th Prandtl numbr incrass th Nusslt numbr also incrass. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of -. is 8.3%, 4.56%, 4.76%, 6.59%, 5.3%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of. -.4 is 6.66%, 6.5%, 5.18%, 8.%, 8.5%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 5.%, 5.18%, 8.%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of is 6.66%, 6.67%, 6.66%, 6.66%, 6.5%. Th prcntag incras of Nusslt numbr at th dpths,,, and for a vlocity of.8-3 is 6.58%, 7.69%, 7.14%, 6.%, 6.5%. Figur 13. Comparison btwn th plat lngth and prssur drop on th hot fluid sid at various dpths Figur 13 shows th ffct of vlocity of th fluid on th prssur drop on th hot fluid sid for a plat lngth of 0.5 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 6.76%, 6.59%, 7.3%, 7.1%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 7.66%, 6.5%, 6.18%, 8.%, 7.0%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 5.18%, 8.%, 8.1%. Th prcntag incras of prssur drop at th dpths,,, and 1000 m for a vlocity of is 6.66%, 6.66%, 6.67%, 6.66%, 6.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 7.58%, 7.69%, 7.14%, 7.%, 6.5%. Figur 14 shows th ffct of vlocity of th fluid on th prssur drop on th cold fluid sid for a plat lngth of 0.5 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 5.76%, 6.59%, 6.%, 6.3%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 6.66%, 6.5%, 6.18%, 8.%, 6.78%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 6.18%, 6.%, 6.3%. Th prcntag incras of prssur drop at th dpths,,, and 1000 m for a vlocity of is 6.66%, 7.76%, 7.66%, 7.66%, 7.%. Th prcntag incras of 999

10 Prssur drop on th cold fluid sid (kpa) Prssur drop on th cold fluid sid (kpa) Prssur drop on th hot fluid sid (kpa) prssur drop at th dpths,,, and for a vlocity of.8-3 is 7.58%, 7.69%, 7.14%, 7.%, 6.5% Vlocity of th fluid (m/s) Vlocity of th fluid (m/s) Figur 15. Comparison btwn th plat lngth prssur drop on th hot fluid sid at various dpths Figur 14. Comparison btwn th plat lngth and prssur drop on th cold fluid sid at various dpths Figur 15 shows th ffct of vlocity of th fluid on th prssur drop on th hot fluid sid for a plat lngth of 0.6 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths 600m, 700m, 800m, 900m and 1000m for a vlocity of -. is 8.3%, 5.76%, 6.59%, 7.3%, 7.%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 7.66%, 7.5%, 7.18%, 8.%, 7.%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 7.7%, 6.18%, 8.%, 7.4%. Th prcntag incras of prssur drop at th dpths, 700 m,, and for a vlocity of is 7.66%, 7.67%, 6.66%, 8.66%, 9.1%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 7.58%, 7.69%, 7.14%, 7.%, 7.5% Vlocity of th fluid (m/s) Figur 16. Comparison btwn th plat lngth prssur drop on th cold fluid sid at various dpths Figur 16 shows th ffct of vlocity of th fluid on th prssur drop on th cold fluid sid for a plat lngth of 0.6 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 5.76%, 7.59%, 6.3%, 6.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 6.66%, 7.5%, 6.18%, 8.%, 6.56%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 6.18%, 8.%, 8.01%. Th prcntag incras of prssur drop at th dpths,,, and 1000 m for a vlocity of is 7.66%, 6.67%, 8.66%, 7.3%, 7.%. Th prcntag incras of prssur drop at th dpths,,, 1000

11 Prssur drop on th hot fluid sid (kpa) Prssur drop on th cold fluid sid (kpa) and for a vlocity of.8-3 is 6.58%, 7.69%, 7.14%, 6.%, 6.5% Vlocity of th fluid (m/s) Vlocity of th fluid (m/s) Figur 17. Comparison btwn th plat lngth prssur drop on th hot fluid sid at various dpths Figur 18. Comparison btwn th plat lngth prssur drop on th cold fluid sid at various dpths Figur 17 shows th ffct of vlocity of th fluid on th prssur drop on th hot fluid sid for a plat lngth of 0.7 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 5.76%, 7.59%, 6.3%. Th prcntag incras of prssur drop at th dpths,,, and 1000m for a vlocity of. -.4 is 7.66%, 7.5%,6.18%,8.%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 6.18%, 6.%. Th prcntag incras of prssur drop at th dpths, 700 m,, and for a vlocity of is 7.66%, 6.77%, 6.96%, 6.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 6.58%, 7.69%, 7.14%, 6.%, 6.5%. Figur 18 shows th ffct of vlocity of th fluid on th prssur drop on th cold fluid sid for a plat lngth of 0.7 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 5.76%, 6.59%, 6.3%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 7.66%, 7.5%, 6.18%, 7.%, 7.13%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.4%, 6.7%, 6.18%, 8.%, 7.98%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 7.66%, 8.67%, 8.66%, 9.66%, 8.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 7.58%, 7.69%, 8.14%, 6.%, 6.78%. Figur 19 shows th ffct of vlocity of th fluid on th prssur drop on th hot fluid sid for a plat lngth of 0.8 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 5.76%, 7.59%, 7.4%, 6.3%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 7.66%, 6.5%, 6.18%, 6.0%, 9.%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 9.4%, 7.7%, 6.18%, 7.1%, 1001

12 Prssur drop on th cold fluid sid (kpa) Prssur drop on th hot fluid sid (kpa) Prssur drop on cold fluid sid (kpa) 8.%. Th prcntag incras of prssur drop at th dpths,,, and 1000 m for a vlocity of is 7.66%, 8.67%, 9.66%, 7.56%, 7.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 6.58%, 7.69%, 7.14%, 6.%, 6.1%. 8.%. Th prcntag incras of prssur drop at th dpths,,, and 1000 m for a vlocity of is 8.66%, 8.67%, 9.66%, 8.5%, 8.66%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of.8-3 is 8.58%,7.69%, 8.14%, 7.%, 7.3%, 7.5% Vlocity of th fluid (m/s) Plat lngth (m) Dpth (m) Figur 19. Comparison btwn th plat lngth prssur drop on th hot fluid sid at various dpths Vlocity of th fluid (m/s) Figur 0. Comparison btwn th plat lngth prssur drop on th cold fluid sid at various dpths Figur 0 shows th ffct of vlocity of th fluid on th prssur drop on th hot fluid sid for a plat lngth of 0.8 m at various dpths. Th prssur drop incrass as th vlocity of th fluid incrass. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of -. is 8.3%, 6.76%, 8.59%, 7.%, 7.3%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of. -.4 is 8.66%, 7.5%, 7.18%, 8.0%, 9.%. Th prcntag incras of prssur drop at th dpths,,, and for a vlocity of is 9.4%, 7.7%, 7.18%, 8.6%, Figur 1. Thr dimnsional plot of plat lngth and dpth v/s prssur drop on th cold fluid sid Figur 1 shows th 3-D optimizd rsults for th minimum prssur drop on th cold fluid sid for various plat lngths and for various dpths of th ocans. It is found that th prssur drop is 5.41 for a dpth of at a plat lngth of 0.3 m. Th prssur drop is 5.3 for a dpth of at a plat lngth of 0.4 m. Th prssur drop is 6.01 for a dpth of at a plat lngth of 0.5 m. Th prssur drop is 5.5 for a dpth of at a plat lngth of 0.6m. Th prssur drop is 5.4 for a dpth of at a plat lngth of 0.7m. Th minimum optimum prssur drop on th cold fluid sid is found to b 5.41 at a dpth of. 100

13 Prssur drop on hot fluid sid (kpa) Ovrall hat transfr (kw/m K) Plat lngth (m) Dpth (m) Plat lngth (m) dpth (m) Figur. Thr dimnsional plot of plat lngth and dpth v/s prssur drop on th hot fluid sid Figur 3. Thr dimnsional plot of plat lngth and dpth v/s ovrall hat transfr cofficint Figur shows th 3-D optimizd rsults for th minimum prssur drop on th hot fluid sid for various plat lngths and for various dpths of th ocans. It is found that th prssur drop is 4.76 for a dpth of at a plat lngth of 0.3 m. Th prssur drop is 4.58 for a dpth of at a plat lngth of 0.4 m. Th prssur drop is 5.01 for a dpth of at a plat lngth of 0.5 m. Th prssur drop is 4.89 for a dpth of at a plat lngth of 0.6 m. Th prssur drop is 4.67 for a dpth of at a plat lngth of 0.7 m. Th minimum optimum prssur drop on th cold fluid sid is found to b 4.76 at a dpth of. Figur 3 shows th 3-D optimizd rsults for th Ovrall hat transfr cofficint on th hot fluid sid for various plat lngths and for various dpths of th ocans. It is found that th ovrall hat transfr cofficint incrass. Th ovrall hat transfr at a dpth of for a plat lngth of 0.3 is 45. Th ovrall hat transfr cofficint at a dpth of for a plat lngth of 0.4 m is 46. Th ovrall hat transfr cofficint at a dpth of for a plat lngth of 0.5 m is 4. Th ovrall hat transfr cofficint at a dpth of for a plat lngth of 0.6 m is Th ovrall hat transfr cofficint at a dpth of for a plat lngth of 0.7 m is 40. Th maximum ovrall hat transfr is found to b 46 at a dpth of 6. Conclusion In this study, a thortical approach has bn proposd to dsign a hat xchangr for a 0.1 MW OTEC plant. Assuming fixd tmpratur for both hot and cold fluids and varying th pip lngth from 0.3 m to 0.7 m and cold fluid suction dpth undr th ocan from to, a minimum prssur drop and hat transfr co-fficint for both hot and cold fluids is obtaind for a crtain pip lngth and cold fluid suction dpth. From th forgoing rsults, it can b concludd as follows: 1. For varying plat lngth and dpths th prssur drop on th cold fluid sid is found to b incrasing. Th prssur drop on th cold fluid sid is found to b fasibl for a dpth of with a prssur drop of 5.3 kpa.. For varying plat lngth and dpths th prssur drop on th hot fluid sid is found to b incrasing. Th prssur drop on th hot fluid sid is found to b fasibl for a dpth of with a prssur drop of 4.58 kpa. 3. For varying plat lngth and dpths th ovrall hat transfr cofficint is found to b incrasing. Th ovrall hat transfr cofficint is found to b fasibl for a dpth of with an ovrall hat transfr cofficint of 46 kw/m K. 7. Nomnclatur A Hat transfr ara, m b Man spacing btwn plats, m C p Spcific hat capacity, kj/kgk D Equivalnt diamtr, m D i Innr diamtr of th tub, m D o Outr diamtr of th tub, m f Friction factor. Mass vlocity, kg/m s G m 1003

14 h Hat transfr cofficint, W/m K k Thrmal conductivity, W/mK L Lngth of th plat, m LMTD Log man tmp. diffrnc,c m Mass flow rat, kg/s N Numbr of plats NTU Numbr of transfr units. Nu Nusslt numbr N p Numbr of passs. Pr Prandtl numbr P Prssur drop, kpa R Rynolds numbr T avg Avrag tmpratur, K T c Tmpratur of cold fluid, K T h Tmpratur of hot fluid, K T Tmpratur diffrnc, K U Ovrall hat transfr cofficint kw/m K u Vlocity of th fluid, m/s w Width of th gaskt, m q Amount of hat transfrrd btwn th fluids, kj/kgk Grk Symbols Dnsity of th fluid, kg/m 3 Viscosity of th fluid, kg/ms 7. Rfrncs [1] H. Blomrius, and N. K. Mitra, Numrical invstigation of convc-tiv hat transfr and prssur drop in wavy ducts, Numrical Hat Transfr, 000, pp [] W.W. Fock, and P. G. Knibb, Flow visualization in paralll-plat ducts with corrugatd walls, J Fluid Mch, Vol. 165, 1986, pp [3] W.W. Fock, J. Zachariads, and L. Olivir, Th ffct of th corrugation inclination angl on th thrmo hydraulic prformanc of plat hat xchangrs, Int. J Hat Mass Transfr, Vol. 8, 1985, pp [4] R. L. Havnr, H. Kumar, and A.S. Wanniarachchi, Prformanc of an industrial plat hat xchangr: ffct of chvron angl, Hat Transfr, Am Inst Chm. Eng., AIChE Symp. 95, Vol 89, [5] P. J. Hggs, P. Sandham, R. A. Hallam, and C. Walton, Local transfr cofficints in corrugatd plat hat xchangrs channls, TransIChmE, Chm.Eng., [6] Hsslgravs, J.E., Compact Hat Exchangrs: Slction, Dsign and Opration, 1st Ed., Prgammon, Nw York, 001. [7] Kays, W.M. and A. L. London, Compact hat xchangrs 3rdEd. Krigr Publ. Co., Florida, [8] K. Mitsutru, and Y. Ikgami, Th Prformanc Evaluation of th plat typ vaporator using th Ammonia / Watr mixturs Procding of th Intrnational Confrnc on Coastal and Ocan Tchnology, 003, pp [9] P. H. G. Alln and T. G. Karayiannis, Rcnt Dvlopmnts in EHD Enhancd Hat Transfr Rnwabl Enrgy, Vol.5, 1995, pp [10] P. Sriyutha Murthy, R. Vnkatsan, K.V.K. Nair, D. Inbakandan, S. Syd Jahan, D. Magsh Ptr, and M. Ravindran, Evaluation of sodium hypochlorit for fouling control in plat hat xchangrs for sawatr application Intrnational Biodtrioration & Biodgradation, Vol. 55, 005, [11] S. V. Paras, E. I. P. Drosos, A. J. Karablas, F. Chopard, Countr-Currnt Gas/Liquid Flow Through Channls with Corrugatd Walls Visual Obsrvations of Liquid Distribution and Flooding, World Confrnc on Exprimntal Hat Transfr, Fluid Mchanics & Thrmodynamics, Thssaloniki, Sptmbr 4-8, 001. [1] S. V. Paras, A.G. Kanaris, A. A. Mouza, A. J. Karablas, CFD cod application to flow through narrow channls with corrugatd walls Intrnational Congrss of Chmical and Procss Enginring, Pragu, 00. [13] Shah, R. K. and A. S. Wanniarachi, Plat hat xchangr dsign thory, J.M. (Ed.). Industrial Hat Exchangrs, Von Karman Institut Lctur Sris ( ). [14] T. Mitsumri, Y. Ikgami and H. Uhara, Advantags of plat typ hat xchangr ovr tub typ hat xchangr for OTEC powr plant, Int. J. Offshor and Polar ngg.,vol.9, [15] N. Tsutomo, and H. Uhara, Shll and tub hat xchangrs for OTEC powr Plants Exprimntal and fluid scinc, [16] H. Uhara, Y. Ikgami, Optimization of a closd-cycl OTEC systm, J. Solar Enrgy Eng. Vol. 11, 1990, pp [17] H. Uhara, Y. Ikgami, and K. Tsuboi, Study on a nw OTEC systm using ammonia and watr as working fluid, JSME Thrmal Enginring Confrnc, 14, 1997, pp [18] S. Wongwiss, Effct of inclination angls and uppr nd conditions on th countrcurrnt flow limitation in straight circular pips, Int. Comm. Hat Mass Transfr, Vol. 5, 1, 1998, pp [19] A. Mouza, S. V. Paras, and A. J. Karablas, Influnc of small tub diamtr and inclination angl on flooding phnomna Intrnational Congrss of Chmical and Procss Enginring, Pragu,