mini project for jntu

8/10/2019 mini project for jntu

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DEPARTMENT OF MECHANICAL ENGINEERING

SREE !AANMAYI INSTITUE OF ENGINEERING TECHNOLOGY

CERTIFICATE

This is to certify that the project report entitled CFDANALYSIS OF HEAT EXCHANGER WITH AND WITHOUT

BAFFLES submitted by

MR.K.BALAJI , bearing roll number 109A1A0311; MR.PRABHAKAR bearing roll number 10651A0314; MR.SRINIVASULU bearing roll number 109A1A0321; MR.K.PHANINDRA KUMAR bearing roll number 119A5A0303;MR.S. KUMARA SWAMY bearing roll number 119A5A0304

in partial ful lment for the award of Degree of Masterof Technology in Mechanical Engineering to the Jawarharlal Nehru Technological University is a recordof bono de wor carried out by him under myguidance and supervision! The result embodied in thisproject report have not been submitted to any otherUniversity or "nstitute for the award of any degree ordiploma!

H& % %&8 ' +&$ .S,8&'5-* ' M.A.FAI=AN

P' &** ' M&/ $-/ 2 E$44. M&/ $-/ 2 E$44D&8 .

S!IET S!IET

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MECHANICAL DEPARTMENT.


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DECLARATION

I here by declare that the work reported in the present thesis titled >CFDANALYSIS OF HEAT EXCHANGER WITH AND WITHOUT BAFFLES

? is a record of work done by me in the Department of Mechanical Engineering,S!IET H6%&' : %.

No part of the thesis is copied from books/journals. he reports are based on the project work done entirely by me and not copied from any other source.

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ACKNOWLEDGEMENT

'irst of all we e)press our grateful thanks to our college 8'-$/-8 2 D'. ESWHAR

who initially initiated and encouraged to do our main project in this semester.

*e e)press our heartfelt gratitude to M.A .FAI=AN (H& % O D&8 ' +&$ ) who

supported us and allotted us a good guide for our project.

*e e)press our sincere thanks and gratitude to MR. SANDEEP for her concern with

constant support and encouragement throughout our project work that helped us in making

our project successful.

*e also e)press our special thanks to PROF@ J.RAMESH BABU , (ead of

Department of Mechanical Engineering, OSMANIA UNI!ERSITY ,who helpedus in the progress of our project and also thanks to our department staff, lab incharge and

students who helped us throughout our project and pro+ided things whate+er we needed

throughout the project.

'inally I would like to thank the almighty for his blessings without which this work could not ha+e been accomplishe d!


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ABSTRACT

In this project an effort is made for 'D analysis of single pass heat e)changer with

and without no--le baffle. In order to analy-e the performance of the heat e)changer, hot

fluid was made to flow inside and cold fluid flows around the body of heat e)changer. he

baffle used in heat e)changer is no--le baffle. he isertion of baffles, force the fluid to ha+e a

turbulent flow, thus impro+ing the heat transfer rate. he results of heat transfer rate for flow

of fluid with no--le baffle in heat e)changer are compared with the heat e)changer without

baffle. he +elocity and temperature profile are analy-ed using the software #N! !

' $EN .

In this project we modeled the heat e)changer tube with and without baffle in the

#N! ! *&%01EN ( and analy-ed it in the #N! ! ' $EN . *e did !tudy of heat

transfer coefficient by +arying %eynolds number and other parameters like temperature,

pressure, enthalpy and entropy of heat e)changers to show the effect of baffles and present a

re+iew of the work.


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TABLE OF CONTENTS

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(#2 E% 7 7.3 &N $!I&N! >. "rowth, aging and hardening and the increase of deposits strength or auto retardation,

erosion and remo+al .

Detailed analysis of deposits from the heat e)changer may pro+ide an e)cellent clue to

fouling mechanisms. It can be used to identify and pro+ide +aluable information about such

mechanisms. he deposits consist primarily of organic material that is predominantly

asphaltenic in nature, with some inorganic deposits, mainly iron salts such as iron sulphide.

he inorganic content of the deposits is relati+ely consistent in most cases at 44 47R .

Deposit analysis is performed by taking a sample and e)tracting any degraded hydrocarbon

oil by using a sol+ent, such as methyl chloride, that is effecti+e at remo+ing hydrocarbon oils

and low molecular weight polymers that may ha+e been trapped in the deposit. he remaining

material from this e)traction will consist of any organic polymers, coke, and inorganic

components. he basic analysis of the non e)tractable material in+ol+es ashing in which

organic and +olatile inorganic compounds are lost. 1y this means, +olatile inorganics such as

chlorides and sulphur compounds which are lost on ashing, may be determined. he detection

of iron sulphide or other +olatile inorganic materials determines the cause of inorganic

fouling. hese +alues can be compared throughout the e)changer train . he non +olatile

material or ash will include all o)idised metallic salt6type materials or corrosion products.

he presence of iron in the ash may indicate corrosion in tankage in an upstream unit or in

the e)changer train itself. his basic analysis indicates if the deposits are primarily organic or

inorganic. !pecial techniGues and tools such as the use of optical microscopy and solubility in

sol+ents may be used for the analysis of the non e)tractable material. Infrared analysis can

identify +arious functional groups present in the deposit which may include nitrogen,

carbonyls, and unsaturated paraffinic or aromatic compounds which are polymerisation#-


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precursors, identified in feed stream characterisation . he carbon and hydrogen content of

the none)tractable deposit can be determined by elemental analysis. If the carbon to hydrogen

ratio is +ery high, it may indicate that the majority of the organic portion of the deposit is

coke. he coke may ha+e been particles entrained in the stream or material which has been

thermally dehydrogenated in the heat e)changers. he carbon to hydrogen ratio also indicates

whether the deposit is more paraffinic or aromatic. his information helps identify the polymers formed .In analytical results are shown from deposits obtained from the four chain

feed/effluent heat e)changers in which the hot product effluent is used for pre heating the

cold naphtha feedstock for a naphtha hydrotreater plant at the (oms &il %efinery . his plant

is one of the most important units at the (oms %efinery, with an annual capacity of 9


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1.5.2. PARTICLES IN THE FEED STREAM

Particles i n the uid feed stream are sol id particles w hich are en trained or contained

in the feed stream before en tering the heat exchanger and which can settle ou t upon

the heat exch anger su rfaces. These so lid particles a re for t he most part insoluble

inorganic particles such as corrosion products (iron sulphide and rust), catalyst

particles or nes, dirt, silt an d sand particles, and other inorganic salts such as

sodium chloride, calcium chloride an d magnesium chloride. The feed streams may

also con tain some organic particles t hat may have b een formed during their storage

or t ransport.

Many streams including cooling water and other pr oduct streams from differentunits or plants may contain solid particles. In particular, streams from such oil

renery units as vacu um units, visbreakers, and cokers m ay have m ore p articulates

and metals than straightrun products due to the heavier nature of the feeds

processed. Streams can also be purchased from other r eners. Due t o the increased

transit time an d exposure t o oxygen before b eing fed to the u nit these feeds m ay h ave

higher particulate levels as a result o f p olymerisation reactions and corrosion

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.Particles i n the uid stream, regardless of whether t hey are o rganic or i norganic in

nature, fall in general into tow classes: basic sed iment and lterable so lids.

Typically, particles i n the uid stream greater t han 1 ptb (pounds per t housand

barrels) lead to s

avoided however if these particles are removed by solid-liquid ltration,

sedimentation, centrifugation or by any of various uid cleaning devices. The only

particles t hat need to be co nsidered in this r egard are t hose t hat are n ot lterable o r

those p articles t hat are l eft to proceed to the h eat exchanger.

The amount of l terable solids in the stream, reported in ptb or w t% (weight

percent), may be d etermined by ltration of the u nit feed. Filterable so lids an alysis

can evaluate a stream deposition potential by indicating the type of materials t hat

could contribute to fouling if allowed to pass through to the h eat exchanger. shows

the a nalysis of lterable sol ids in the n aphtha feed stream to the h eat exchangers of

the h ydrotreater u nit at the H oms oi l renery. The f eedstock for t his u nit is a b lend oflight and heavy straight-run naphtha f ractions f rom four different topping units. The

resulting blend is left in a blending tank for a su fficient period of time to allow for

equilibrium conditions t o be established . To evaluate the quantity of p articulate

solids which are entrained with the naphtha stream before entering the heat

exchangers, a number of samples of the naphtha feed were ltered and the amount

of entrained particles d etermined. Two samples o f the lterable solids w ere taken,one sample was taken from the feed entering a m acrolter on the unit boundary and

the other from a second macrolter on the feed pump suction. The nature of the

materials entrained was then determined by ashing and analysing these two sam ples

. The si ze distribution of the lterable so lid particles w as al so d etermined .

1.5.2.1.PARTICLE FORMATION

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hemical particle formation is the basic mechanism of particle formation in heat e)changers

fluid streams, although organic material growth and biological particle formation, or

biofouling, ay occur in sea water systems and in types of waste treatment systems. 1iofouling

may be of two kindsH microbial fouling, due to microorganisms bacteria, algae, and fungiJ

and their products, and macrobial fouling, due to the growth of macroorganisms such as barnacles, sponges, seaweeds or mussels. &n contact with heat transfer surfaces, these

organisms can attach and breed, reducing thereby both flow and heat transfer to an absolute

minimum and sometimes completely clogging the fluid passages. !uch organisms may also

entrap silt or other suspended solids and gi+e rise to deposit corrosion. orrosion due to

biological attachment to heat transfer surfaces is known as microbiologically C &+-/ 2

8 ' -/2& '+ - $ can be the result of either corrosion or decomposition and polymerisation

reactions. race contaminants present in the fluid stream can ha+e a influenced corrosion. 'or open recirculating systems, bacteria concentrations of the order of 3 ) 3@> cells/ml and fungi

of 3 ) 3@8 cells/ml may be regarded as limiting +alues significant effect on the fouling

encountered in certain chemical processes. !uch contaminants may include o)ygen, nitrogen,

N(8, (4!, N, ( N, (g, unsaturates, organic sulphides and chlorides, and hea+y

hydrocarbon compounds such as paraffin wa), resins, asphaltenes, and organometallic

compounds. Indi+idual metals, which may e)ist as metal salts in the feed stream, can catalyse

different polymerisation reactions. he concentrations of such metals are typically +ery low,not e)ceeding few ppms. (owe+er, small concentrations of certain metals can ha+e a

significant effect on catalysing different foulingrelated polymerisation reactions. Metal

detectors on unit feed samples can detect indi+idual metals in the stream at less than 3 ppm.

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Corrosion fouling is fouling deposit formation as a result of the corrosion of the

substrate metal of h eat t ransfer su rfaces. This type of co rrosion should not b e

confused, however, with the u nder-deposit corrosion, referred to earlier, which is on e

of the af tereffects of fouling. Corrosion fouling is a m echanism which is d ependent

on several factors su ch as t hermal resistance, surface rou ghness an d composition of

the substrate and uid stream. In particular, impurities p resent i n the uid stream

can greatly contribute to the onset of c orrosion. Such impurities i nclude hydrogen

sulphide, ammonia an d hydrogen chloride. In crude oil, for exam ple, sulphur and

nitrogen compounds are two very common contaminants which are mostly

decomposed in certain situations to hydrogen sulphide an d ammonia respectively.

Chlorides which m ay be found in oil streams ar e conv erted to hydrogen chloride by

the f ollowing reaction.

R-Cl + H 2 HCl + R

he chlorides may enter the refinery as salt with the crude. hlorides in the oil stream may

also be deri+ed from +arious chemicals used in the oil industry which can contain highle+els

of chloride. !uch chemicals include tertiary oil reco+ery enhancement chemicals andsol+ents

used to clean tankers, barges, trucks and pipelines. #s the crude oil is processed some of thesechemicals and sol+ents, which are thermally stable and not soluble in water,pass o+erhead in

the main tower of the atmospheric distillation unit along with the naphtha.In the hydrotreater

feed stream, chloride le+els as high as >@ wt. ppm ha+e been reported.(igh le+els of chloride

were detected with the filterable solids in the naphtha feed stream tothe heat e)changers of

the hydrotreater unit at the (oms refinery able 8J and in thedeposits obtained from the heat

e)changers able 4J. 'urthermore, the makeup hydrogenfrom the platforming unit will

always contain trace Guantities of hydrogen chloride. In orderto maintain catalyst

performance, modern platforming catalysts reGuire a small, butcontinuous dosage of chloride,

some of which is always stripped and lea+es the platformingunit in the net gas stream that

supplies the hydrotreater with makeup hydrogen.In a hydrogen sulphide en+ironment the

sulphur reacts with the e)posed iron to form ironsulphide compounds. his happens in both

the hot and cooler sections of the unit. he sulphureffecti+ely corrodes the plant. (owe+er,

once reacted, the iron sulphide forms a comple)protecti+e scale or lattice on the base metal,

which inhibits further corrosion. he sulphidelattice would remain in eGuilibrium with its

surroundings and the corrosion rate would be minimal if no other impurities were present in

the system. he presence of other impurities,$'


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howe+er, can accelerate corrosion as these impurities interact with the sulphide lattice. &f the

impurities that contribute to corrosion and fouling, hydrogen chloride may be the most

important. 1y itself hydrogen chloride does not cause a problem. It will not fouleGuipment or

corrode the carbon steel in the unit. hloride corrosion and fouling, howe+er, take place when

hydrogen chloride, ammonia, and water all interact in the colder sections of the unit to defeat

the protecti+e sulphide lattice. he e)tent of the damage depends on their concentration and isdirectly dependent on p(, with the corrosion rate increasing rapidly with p( decrease.

(ydrogen chloride will become corrosi+e when it comes in contact with free water, i.e. water

that is not in the +apour phase or is not saturated in the liGuid hydrocarbon. &il products are

almost always saturated with water, and entrained water, e+en if it is less of a problem, does

occur in most cases. 'urthermore, continuous water wash at key locations is recommended as

part of the solution to minimise the effects of chloride corrosion and fouling and this further

contributes to the total water in the system. (ydrogen chloride is highly soluble in water, and

in a free water en+ironment, any hydrogen chloride present in the +apour or hydrocarbon

liGuid will be Guickly absorbed by the water, thus dri+ing the p( down to appro)imately 3.

If the iron sulphide lattice is intact this chloride competes with the bisulphate ion !( J for

the iron ions in the latticeH

! 'e ! 'e !( U l 'e ! ! 'e l U !(*ith

a high concentration of hydrogen chloride present the reaction shifts to the right. #s more and

more bisulphate is released from the sulphide lattice, it e+entually dissol+es.

$(


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CHAPTER "

".1 LITERATURE AND RE!IEW

( eat e)change de+ice s ar e essential component s in comple) enginee r ing

system s r elated to ene r gy gene r ation and ene r gy t r ansf or mation in indu str ial

scenes. Modeling o f shell and tube heat e)change r , f or design and pe rf or mance

e+aluation, i s now an e stablished techniGue in indu str ial f ields. In thi s pape r ,

heat e)change rs with ba ff les based on pe r iodic bounda r ies ha+e been simulated.

# ll po ssible attempt s wer e made to obtain the in f luence o f baff le s pace s on f luid

f low and heat t r ansf er on the shell side o f by u sing the same geomet r ical and

the r mo ph ys ical condition s. he r esults of simulation s indicate that f or the same

mass f low r ate, the heat t r ansf er pe r unit a r ea dec r eases with the inc r ease o f ba ff le

s pace sL howe+er , f or the same p r essur e dr op, the mo st e)tended ba ff le s pace

obtain s highe r heat t r ansf er . *e al so f ound out that the p r essur e gr adient

decr eases with the inc r ease o f ba ff les s pace.

' or many years, shell and tube heat e)change rs ! (:sJ ha+e been the

most widely u sed eGuipment in the indu str ial f ields includingH power plant,

pet r oleum r ef ining, steam gene r ation, etc. ! (:s pr o+ide r elati+ely la r ge r atios o f

heat t r ansf er ar ea to +olume and weight and can be ea sily cleaned 1a ff les ar e one

of the mo st impo r tant pa r ts of ! (:s , they f or ce the f luid o f shell side to f low

acr oss the tube s to en sur e high heat t r ansf er r ates and al so pr o+ide suppo r t f or tube

bundle. he r e ar e di ff er ent type s of ba ff le a rr angement u sed in shell and

tube heat e)change rs. he mo st commonly u sed ba f .es, called segmentalba f .es,

cause the shellEside f luid to f low in a -ig-ag manne r acr oss the tube bundle. hi s

action imp r o+es heat t r ansf er by enhancing tu r bulence or local mi)ing on the

shell sideL howe+er , it al so inc r eases the shell side p r essur e d r op and r eGuir es a

gr eat pumping power andL as a r esult, inc r eases elect r icity con sumption. ( igh

r ange o f dead -one s, back.o ws and high r isk o f +ibr ation f ailur e on the tube

bundle a r e othe r Disad+antage s of abo+eEmentioned ba ff le type s. 1a ff le s pacing

and ba ff le cut r atio. ! ome autho rs cons ider ed the co st of heat t r ansf er surf ace

ar ea o r capital in+e stment a s an objecti+e f unction to be minimi-ed *hile

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othe rs con sider ed the sum o f in+estment r elated to the heat t r ansf er surf ace

ar eaJand ope r ational f luid head lo ssesJ costs as an objecti+e f unction f or

optimi-ing a shell and tube heat e)change r he sum o f ent r opy gene r ation o f

str eam s as an objecti+e f unction was also r epo r ted in MultiEobjecti+e optimi-ation

of total annuali-ed co st and the amount o f cooling wate r r eGuir ed f or shell and

tube heat e)change r was studied in r ef er ence .( ilber t et al. al so, used a multi Eobjecti+e optimi-ation techniGue to ma)imi-e the heat t r ansf er r ate and to

minimi-e the p r essur e dr op in a tube bank heat e)change r . iu and heng

optimi-ed a r ecupe r ate f or the ma)imum heat t r ansf er eff ecti+ene ss as well a s

minimum e)change r weight and p r essur e lo ss. In thi s pape r af ter the r mal modelling

of an indu str ial shell and tube.

MultiEobjecti+e optimi-ation o f shell and tube heat r eco+er y heat e)change r was

perf or med with e ff ecti+ene ss and total co st as two objecti+e s not selected in

othe r a+ailable lite r atu r eJ using genetic algo r ithm.V

he tube a rr angement, tube diamete r , tube pitch r atio, tube length, tube numbe r ,

ba ff le s pacing r atio a s well a s ba ff le cut r atio wer e selected a s design pa r amete rs

not selected a s a gr oup o f +ar iables in othe r a+ailable lite r atu r eJ.V

# clo sed f or m eGuation f or the total co st in te r m o f eff ecti+ene ss at the optimal

design point was pr opo sed. hi s eGuation can be modelled without change in it s

pr ocedu r e o f der i+ing f or any ne w input +alue s.V ! ensiti+ity analy sis of change

in objecti+e f unction s when the optimum de sign pa r amete rs +ar y was perf or med.

4.4 BA FF LI NG

".".1 TY PE O F BAFF LE S@ 1a ff les ar e used to suppo r t tube s, enable adesir able +elocity to be maintained f or the shell side f luid, and p r e+ent f ailu r e

of tube s due to f lowEinduced +ib r ation. he r e ar e two type s of ba ff lesH plate and

r od. 2 late ba ff les may be single Esegmental, double Esegmental, o r tr ipleE

segmental, a s shown in ' igu r e 3

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"."." BAFFLES SPACING @

1a ff le s pacing i s the centr elineEtoEcentr eline di stance bet ween adjacent ba ff les.

It is the mo st +ital pa r amete r in ! ( E de sign. he E M# standa r ds s peci f y

the minimum ba ff le s pacing a s one Ef if th of the shell in side diamete r or 4 in.,

whiche+e r is gr eater . lo ser s pacing will r esult in poo r bundle penet r ation by

the shell side f luid and di ff iculty in mechanically cleaning the out.

' ig.3 ype s of 1a ff les

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' ig. 4. 2ositions of per iodic bounda r ies ba ff le pitch and ba ff le s pace.

! ides of the tube s. ' ur the r mo r e, a lo w ba ff le s pacing r esult s in a poo r str eam

distr ibution a s will be e)plained late r .

he ma)imum ba ff le s pacing i s the shell in side diamete r . ( ighe r ba ff le s pacing

will lead to p r edomina ntly longitudinal f low, which i s less eff icient than c r ossE

f low, and la r ge un suppo r ted tube s pan s, which will make the e)c hange r pr one totube f ailur e due to f lowEinduced +ib r ation. & ptimum baff les pacing. ' or

tur bulent f low on the shell side %e W 3,@@@J, the heat Etr ansf er coe ff icient +a r ies

to the @.76@.; power of +elocityL howe+er , pr essur e dr op +ar ies to the 3.;64.@

power . ' or lamina r f low %e X 3@@J, the e)ponent s ar e @.88 f or the heat Etr ansf er

coe ff icient and 3.@ f or pr essur e dr op. hu s, as ba ff le s pacing i s r educed, p r essur e

dr op inc r eases at a much f aster r ate than d oes the heat Etr ansf er coe ff icient. hi s

mean s that the r e will be an optimum r atio o f ba ff le s pacing to shell in sidediamete r that will r esult in the highe st eff iciency o f con+e rsion o f pr essur e dr op to

heat t r ansf er . hi s optimum r atio i s no r mally bet ween @.8 and @.7.

".".3 BA FF LE C UT@

#s shown in ' igu r e 4, ba ff le cut i s the height o f the segment that i s cut i n each

ba ff le to pe r mit the shell side f luid to f low acr oss the ba ff le. hi s is e)p r essed a s a

per centage o f the shell in side diamete r . # lthough thi s, too, i s an impo r tant%.


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par amete r f or ! ( E de sign, it s eff ect is less p r of ound than that o f ba ff le s pacing.

1a ff le cut can +a r y bet ween 3>R and 9> R of the shell in side diamete r . 1oth +e r y

small and +e r y la r ge ba ff le cut s ar e det r imental to e ff icient heat t r ansf er on the

shell side due to la r ge de+iation fr om an ideal situation, a s illustr ated in ' igu r e

8. It is str ongly r ecommended that only ba ff le cut s bet ween 4@R and 8> R be

employed. %educing ba ff le cut belo w 4@R to inc r ease the shell side heat Etr ansf er coe ff icient o r inc r easing the ba ff le cut beyond 8> R to dec r ease the shell side

pr essur e dr op u sually lead to poo r designs. &the r as pect s of tube bundle

geomet r y should be changed in stead to achie+e tho se goal s. ' or e)ample, double

segmental ba ff les or a di+ided Ef low shell, o r e+en a c r ossEf low shell, may be

used to r educe the shell side p r essur e dr op. ' or singleE pha se f luids on the shell

side, a ho r i-ontal ba ff le cut ' igu r e4J is r ecommended, becau se this minimi-e s

accumulation o f depo sits at the bottom o f the shell and al so pr e+ents

str atif ication. ( owe+er , in the ca se o f a twoE pass shell EM# 'J , a +e r tical cut

is pr ef err ed f or ease o f f abr ication and bundle a ssembly. 1a ff ling i s discussed in

gr eater detail in ( 2 ) and ( 3 ).

' ig.4 1a ff le cut

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' ig.8 E ff ect o f small and la r ge ba ff le cut s

".3 E U ALI=E CRO SS;F LO W AND W IND O W !ELOCI T IE S@

' low ac r oss tube s is r ef err ed to a s cr ossEf low, wher eas f low th r ough the window

ar ea that i s, th r ough the ba ff le cut a r eaJ is r ef err ed to a s windo w f low. he

windo w +elocity a nd the c r ossEf low +elocity should be a s clo se as po ssi ble F

pr ef er ably within 4@R of each othe r . If they di ff er by mo r e than that, r epeated

accele r ation and decele r ation take place along the length o f the tube bundle,

r esulting in ine ff icient con+e rsion o f pr essur e dr op to heat t r ansf er .

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". R E !I EW R EL ATE D TO DE SI G N OF STHE

Y,*, A2- K ' O : -2&$ G , ' ' *@ 2r epa r ed a compute r based de signmodel f or pr elimina r y de sign o f shell and tube heat e)change rs with single pha se

f luid f low both on shell and tube side. he p r ogr am dete r mine s the o+e r alldimen sion s of the shell, the tube bundle, and optimum heat t r ansf er surf ace a r ea

r eGuir ed to meet the s peci f ied heat t r ansf er duty by calculating minimum o r

allowable shell side p r essur e dr op.

( e concluded that ci r culating cold f luid in shellEside ha s some ad+antage s on hot

f luid a s shell str eam since the f or mer cau ses lower shellEside p r essur e dr op and

r eGuir es smalle r heat t r ansf er ar ea than t he latte r and thu s it is bette r to put thestr eam with lo wer ma ss f low r ate on the shell side becau se o f the ba ff led s pace.

S, T ) &( M $ T ) $ K ) -$ A,$ 4 L-$ M- S $% ' M $@ In this pape r data i s e+aluated f or heat t r ansf er ar ea and p r essur e dr op and checking

whethe r the a ssumed de sign sati sf ies all r eGuir ement o r not. he p r ima r y aim o f

this design is to obtain a high heat t r ansf er r ate without e)ceeding the allo wable

pr essur e dr op.

he dec r easing patte r n o f cur +es of %eynolds Numbe r and heat t r ansf er

coe ff icient shown in f igur e 9 and f igur e > shows that the %e and h a r e gr adually

dec r eases co rr es ponding a s high a s tube e ff ecti+e length. "r adual dec r ease in

%eynolds Numbe r mean s the r e is signi f icant dec r ease in p r essur e dr op r es pecti+ely.

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' igu r e 9H %eynolds Numbe r on Numbe r of 1a ff les and ength o f ube.

' igur e >H( eat r ansf er oe ff icient on Numbe r of 1a ff les and ength o f ube.

".# L ITE RA T UR E R E !I EWR EL ATE D TO DI FFE R E NT OPT IM I= AT IO N

TE C H NI UE S@

R &* ( S&2: * O $%&' K 27 $ M '/ ,* R &88 -/ )@ # pplied geneticalgo r ithm s "#J f or the optimal de sign o f shellEandEtube heat e)change r by

+ar ying the de sign +a r iablesH outer tube diamete r , tube layout, numbe r of tube passes, oute r shell diamete r , ba ff le s pacing and ba ff le cut. 'r om thi s study it

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was concluded that the combinato r ial algo r ithms such a s "# pr o+ide

signi f icant imp r o+ement in the optimal de signs compa r ed to the t r aditional

design s. "# application f or dete r mining the global minimum heat e)change r

cost is signif icantly f aster and ha s an ad+antage o+e r othe r method s in obtaining

multiple solution s of same Guality.

S&8&) ' S $ 6& H ** $ H G :% 22 ) -@ consider ed se+en de sign par amete rs namely tube a rr angement, tube diamete r , tube pitch r atio, tube

length, tube numbe r , ba ff le s pacing r atio a s well a s ba ff le cut r atio. ' ast and

elitist non Edominated sor ting genetic algo r ithm with continuou s and di scr ete

+ar iables was applied to o btain the ma)imum e ff ecti+ene ss heat r eco+er yJ and the

minimum total co st as two objecti+e f unction s.

! .K. P (&2 R .! . R @ e)plo r es the u se o f a non Etr aditional optimi-ationtechniGueL called par ticle swar m optimi-ation 2!&J , f or design optimi-ation o f

shellEandEtube heat e)change rs fr om economic +ie w point. M inimi-ation o f

total annual co st is con sider ed a s an objecti+e f unction. h r ee de sign +ar iable s

such a s shell inte r nal diamete r , oute r tube diamete r and ba ff le s pacing a r e

con sider ed f or optimi-ation. wo tube layout s +i-. t r iangle and sGuar e ar e

also con sider ed f or optimi-ation.

he p r esented 2!& techniGueYs abilit y is demon str ated u sing di ff er ent lite r atu r e

case studie s and the pe rf or mance r esults ar e compa r ed with tho se obtained by

the p r e+ious r esear che rs. 2!& con+e r ges to optimum +alue o f the objecti+e

f unction within Guite f ew gene r ations and thi s f eatu r e signif ies the impo r tance o f

2!& f or heat e)change r optimi-ation.

In a compute rE based de sign, many

thou sands o f alte r nati+e e)change r con f igur ations may be e)amined. ompute r

codes f or design a r e o r gani-ed to +a r y systematically the e)change r par amete rs

such a s, shell diamete r , ba ff le s pacing, n umbe r of tubeEside pa ss to identi f y

con f igur ations that satisf y the s peci f ied heat t r ansf er and p r essur e dr ops. #

compute rE based de sign model was made f or pr elimina r y de sign o f shellEand tube

heat e)change rs with singleE pha se f luid f low both on shell and tube side. he

pr ogr am co+e rs segmental baff led $Etube, and f i)ed tube sheet heat e)change rs%'


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one E pass and t woE pass f or tube Eside f low. he p r ogr am dete r mine s the o+e r all

dimen sion s of the shell, the tube bundle, and optimum heat t r ansf er surf ace

ar ea r eGuir ed to meet the s peci f ied heat t r ansf er duty by calculating

minimum o r allo wable shellEside p r essur e dr op.

HIn thi s pape r , an optimi-ation p r ogr amhas been u sed to calculate the optimum ba ff le s pacing and the numbe r of sealing

str ips f or all type s o f shell and tube heat e ) change rs, u sing the p r ocedu r e in ( ED(

heat e)change r design hand book J. # set o f co rr elation i s pr esented f or

dete r mining the optimum ba ff le s pacing wide r ange o f design input s peci f ication

data a r e con sider ed f or all type s of shell and tube e)change rs, and thei r optimum

e)change rs f or di ff er ent +alue s of * 3 heat t r ansf er ar ea weight f acto rJ. hi s

e+aluation lead s to co rr elation f or dete r mining the optim um ba ff le s pacing.

Descr ibes to con sider suitable

ba ff le s pacing in the de sign p r oce ss, a compute r pr ogr am ha s been de+eloped

which enable s designe rs to dete r mine the optimum ba ff le s pacing f or

segmental ba ff led shell and tube conden sers. h r oughout the cu rr ent r esear ch, a

wide r ange o f design input data s peci f ication f or E and Z type s shell and t u be

conden sers ha+e been con sider ed and thei r co rr es ponding optimum de signs f or

diff er ent +alue s of * 3 ha+e been e+al uated. hi s e+aluation ha s been led to some

corr elation f or dete r mining the optimum ba ff le s pacing.

studied that the optimum r atio o f ba ff le s pacing to shell

diamete r is dete r mined by applying the the r mo economic analy sis method.# lthough the r e is no p r ecise c r iter ion to dete r mine ba ff le s pacing in the lite r atu r e,

it is ob+iou s that the r mo economic analy sis, as de f ined in thi s pape r , is a po werf ul

tool f or dete r mining o f the optimum ba ff le s pacing. he r esults obtained,

corr es ponding to the di ff er ent objecti+e f unction s, ar e also di scussed. he

r esults of the se method s ar e then u sed to demon str ate ho w the optimum ba ff le

s pacing r atio i s aff ected by the +a r ying +alue s of the heat e)change r geomet r ical

par amete rs.

%(


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CHAPTER 3

3.1 CFD METHODOLOGY

'D can be used to determine the performance of a component at the design stage, or it can

be used to analy-e difficulties with an e)isting component and lead to its impro+ed design.

'or e)ample, the pressure drop through a component may be considered e)cessi+eH

he first step is to identify the region of interestH

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he geometry of the region of interest is then defined. If the geometry already e)ists in #D,

it can be imported directly. he mesh is then created. #fter importing the mesh into the pre

processor, other elements of the simulation including the boundary conditions inlets, outlets,

and so onJ and fluid properties are defined. he flow sol+er is run to produce a file of results

that contains the +ariation of +elocity, pressure and any other +ariables throughout the region

of interest. he results can be +isuali-ed and can pro+ide the engineer an understanding of the beha+ior of the fluid throughout the region of interest.

his can lead to design modifications that can be tested by changing the geometry of the 'D

model and seeing the effect.

he process of performing a single 'D simulation is split into four componentsH

3. reating the "eometry/Mesh

4. Defining the 2hysics of the Model

8. !ol+ing the 'D 2roblem

9. =isuali-ing the %esults in the 2ost processor

3.1.1 CREATING THE GEOMETRY MESH

his interacti+e process is the first pre processing stage. he objecti+e is to produce a mesh

for input to the physics pre processor. 1efore a mesh can be produced, a closed geometric

solid is reGuired. he geometry and mesh can be created in the Meshing application or any of

the other geometry/mesh creation tools. he basic steps in+ol+eH

3. Defining the geometry of the region of interest.

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4. reating regions of fluid flow, solid regions and surface boundary names.

8. !etting properties for the mesh. his pre processing stage is now highly automated. In

':, geometry can be imported from most major #D packages using nati+e format, and the

mesh of control +olumes is generated automatically.

3.1.1.1. DEFINING THE PHYSICS OF THE MODEL

his interacti+e process is the second pre processing stage and is used to create input reGuired

by the !ol+er. he mesh files are loaded into the physics pre processor, ': 2re.

his can lead to design modifications that can be tested by changing the geometry of the 'D

model and seeing the effect.

he process of performing a single 'D simulation is split into four componentsH

3. reating the "eometry/Mesh

4. Defining the 2hysics of the Model

8. !ol+ing the 'D 2roblem

9. =isuali-ing the %esults in the 2ost processor

CREATING THE GEOMETRY MESH

his interacti+e process is the first pre processing stage. he objecti+e is to produce a mesh

for input to the physics pre processor. 1efore a mesh can be produced, a closed geometric

solid is reGuired. he geometry and mesh can be created in the Meshing application or any of

the other geometry/mesh creation tools. he basic steps in+ol+eH

3. Defining the geometry of the region of interest.

4. reating regions of fluid flow, solid regions and surface boundary names.

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#n iterati+e approach is reGuired because of the nonlinear nature of the eGuations, and

as the solution approaches the e)act solution, it is said to con+erge. 'or each iteration,

an error, or residual, is reported as a measure of the o+erall conser+ation of the flow

properties. (ow close the final solution is to the e)act solution depends on a number of

factors, including the si-e and shape of the control +olumes and the si-e of the final

residuals. omple) physical processes, such as combustion and turbulence, are often modeled

using empirical relationships. he appro)imations inherent in these models also contribute to

differences between the 'D solution and the real flow. he solution process reGuires no user

interaction and is, therefore, usually carried out as a batch process. he sol+er produces a

results file that is then passed to the post processor.

3.1.3 !ISUALI=ING THE RESULTS IN THE POST;PROCESSOR

he post processor is the component used to analy-e, +isuali-e and present the results

interacti+ely. 2ost processing includes anything from obtaining point +alues to comple)

animated seGuences.

E)amples of some important features of post processors areH

[ =isuali-ation of the geometry and control +olumes

[ =ector plots showing the direction and magnitude of the flow

[ =isuali-ation of the +ariation of scalar +ariables +ariables that ha+e only magnitude, not

direction, such as temperature, pressure and speedJ through the domain

[ Auantitati+e numerical calculations


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[ #nimation

[ harts showing graphical plots of +ariables

[ (ardcopy and online output.

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CHAPTER

.1 EXISTING MODEL AND ITS DESIGN@

In single tube !urface heat e)changers, the hot fluid flows inside the tube and the cold fluid

flows around the walls of the tube. he heat transfer takes place from inside of the tube to the

walls of the tube. he coolant that flows around the tube carries away the heat.

he main ad+antages of surface heat e)changer areH

hey can be easily designed and constructed.hey are +ery cheap.

Ease of maintenance.(andling the fluids is +ery con+enient.

1ut the main disad+antage of this is its low heat transfer rate.

he line diagram of the surface heat e)changer without baffles as shown abo+e is

designed in #N! ! work bench and analysed in #N! ! ' $EN .

&%

/old

1ot0uidin

1ot0uidout

/old


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." BOUNDARY AND CELL =ONE CONDITIONS

T & B ,$% '6 $% & /&22 $& / $%- - $* 882-&% %,'-$4 & $ 26*-*@

Inlet hot fluid temperatureInlet +elocity of hot fluid*all temperature

Materialype of fluid

IN E (& ' $ID EM2E%# $%E H (ot fluid is the working fluid. *e allow it to flow

inside the tube. he hot fluid coming out from the industry should be cooled. %educing the

temperature of that hot fluid is our main intention. !o we chose one of the boundary

conditions as the inlet temperature of hot fluid.

IN E =E & I &' (& ' $IDH he hot fluid is allowed to pass through the tube

flowing with specific +elocity. #s the +elocity decreases the heat transfer rate increases. he

+elocity plays a major role, so we took its as one of the boundary conditions.

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*# EM2E%# $%EH he wall temperature acts as the coolant temperature since the

coolant surrounds the wall. he heat transfer takes place through the walls. !o the wall

temperature is takes as one of the boundary conditions.

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M# E%I# H he metal with which the heat e)changer is made also plays a major role. !ince

the heat transfer coefficient of the heat e)changer also depends on the type of material.

2E &' ' $IDH he types of fluids that we are using in the heat e)changers are also

considered as cell -one conditions.

.3 ASSUMPTIONS@

Inlet hot fluid temperature H ;?8k Inlet +elocity of hot fluid H 9>m/s*all temperature H 4?8k Material H #luminium

ype of fluid H #ir

. E UATION* USED@

he 0 epsilon model is one of the most common turbulence models , although it just

doesnYt perform well in cases of large ad+erse pressure gradients %eference 9J. It is a two

eGuation model , that means, it includes two e)tra transport eGuations to represent the

turbulent properties of the flow. his allows a two eGuation model to account for history

effects like con+ection and diffusion of turbulent energy.

&(
http://www.cfd-online.com/Wiki/Turbulence_modelinghttp://www.cfd-online.com/Wiki/Two_equation_modelshttp://www.cfd-online.com/Wiki/Two_equation_modelshttp://www.cfd-online.com/Wiki/Turbulence_modelinghttp://www.cfd-online.com/Wiki/Two_equation_modelshttp://www.cfd-online.com/Wiki/Two_equation_models


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he first transported +ariable is turbulent kinetic energy, . he second transported

+ariable in this case is the turbulent dissipation, . It is the +ariable that determines the

scale of the turbulence, whereas the first +ariable, , determines the energy in the

turbulence.

here are two major formulations of 0 epsilon models. hat of aunder and !harma

is typically called the T!tandardT 0 epsilon Model . he original impetus for the 0 epsilonmodel was to impro+e the mi)ing length model, as well as to find an alternati+e to

algebraically prescribing turbulent length scales in moderate to high comple)ity flows.

T' $*8 ' & , - $* ' * $% '% 7;&8*-2 $ + %&2

'or k

For dissipation

M %&2-$4 ,':,2&$ 5-*/ *- 6

urbulent +iscosity is modeled asH

P' %,/ - $ 7

*here is the modulus of the mean rate of strain tensor, defined as H

E &/ :, 6 $/6

*here 2r t is the turbulent 2randtl number for energy

gi is the component of the gra+itational +ector in the i th direction.

&*
http://www.cfd-online.com/Wiki/Standard_k-epsilon_modelhttp://www.cfd-online.com/Wiki/Prandtl_numberhttp://www.cfd-online.com/Wiki/Standard_k-epsilon_modelhttp://www.cfd-online.com/Wiki/Prandtl_number


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'or the standard and reali-able models, the default +alue of 2r t is @..

he coefficient of thermal e)pansion, , is defined as

M %&2 / $* $ *

&+


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CHAPTER #

#.1 SOLUTION INITIALISATION@

he sol+er works in an iterati+e manner.

herefore before the +ery first iteration, a+alue must e)ist for e+ery Guantity in e+ery

grid cell.

!etting this +alue is called \Initiali-ation

(ere in this analysis we initiali-e from the inlet.

#." RUN CALCULATION@

he sol+er should be gi+en sufficient iterations such that the problem is / $5&'4&%

#t con+ergence, the following should be satisfiedH

6 he solution no longer changes with subseGuent iterations.&-


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#.3 PLOTS AND GRAPHS

'$


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#.3.1 TOTAL TEMPERATURE

'%


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#.3." !ELOCITY

'&


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#.3.3 TURBULENCE

''


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#.3. REYNOLDS NUMBER

'(


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#.3.# THERMAL CONDUCTI!ITY

#.3. SURFACE HEAT TRANSFER COEFFICIENT

'*


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#. PROPOSED MODEL AND ITS DESIGN@

In this we introduced a no--le baffle inside the tube at the entrance of hot fluid. !o

that it creates turbulence in the flow and most of the fluid passes along the sides of the wallthus impro+ing the heat transfer rate. his baffle will increase the efficiency of the surface

heat e)changer.

THE MAIN AD!ANTAGE@

(igh heat transfer rate

he line diagram of the proposed design is shown below

'+

/old

1ot0uidout

/old

1ot0uidin


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#. .1 BOUNDARY AND CELL =ONE CONDITIONS@

Inlet temperature of hot fuild ] ;?8k Inlet +elocity of hot fluid ] 9>m/sec*all temperature ] 4?8k Material ] #luminuim

ype of 'luid ] #ir

'-


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(.


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#. ." E UATION USED@

(#


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#.#SOLUTION INITIALISATION@

#.#.1 RUN CALCULATION@

($


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#. PLOTS AND GRAPHS@

(%


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#. .1 TOTAL TEMPERATURE

(&


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#. ." !ELOCITY

('


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#. . REYNOLDS NUMBER

#. .# THERMAL CONDUCTI!ITY

(*


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#. .# SURFACE HEAT TRANFER COEFFICIENT

(+


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CHAPTER ;

.1 CONCLUSION

In the current project, 'D analysis of single pass heat e)changer was done to

e+aluate the performance of a single pass surface heat e)changer with and without baffles

situated at the no--le.

Due to introduction of the baffles, the main modification is implicated by the

considerably large change in the turbulence. his change in turn leads to more heat transfer rate as the working fluid interacts more efficiently with the coolant. hus the primary goal of

high heat transfer is achie+ed using baffles. his can be more clearly obser+ing the

comparisons of different parameters in+ol+ed and plotting their histograms, contours and

simulations performed in #N! !. #nd so, we can conclude that the output results coming

out from heat e)changer ha+ing baffles are more efficient from heat e)changer without

baffles.

hese conclusions directly imply that for low capacity heat e)changer application,

one must not neccessesarily go for a costly heat e)changer. Instead, by installing baffles in

the surface type heat e)changer, its efficiency can be increased considerably.

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mini project for jntu

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