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International Journal of Engineering Research and Development e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com Volume 8, Issue 12 (October 2013), PP. 06-18 6 Numerical modelling of heat transfer in a channel with transverse baffles M.A. Louhibi 1 , N. Salhi 1 , H. Bouali 1 , S. Louhibi 2 1 Laboratoire de Mécanique et Energétique, Faculté des Sciences, BP. 717 Boulevard Mohamed VI - 60000 Oujda, Maroc. 2 Ecole National des sciences Appliquées, Boulevard Mohamed VI - 60000 Oujda, Maroc. Abstract:- In this work, forced convection heat transfer inside a channel of rectangular section, containing some rectangular baffle plates, is numerically analyzed. We have developed a numerical model based on a finite-volume method, and we have solved the coupling pressure-velocity by the SIMPLE algorithm [6]. We show the effects of various parameters of the baffles, such as, baffle’s height, location and number on the isotherms, streamlines, temperatures distributions and local Nusselt number values. It is concluded that: I) The baffles location and height has a meaningful effect on isotherms, streamlines and total heat transfer through the channel. (II) The heat transfer enhances wit h increasing both baffle’s height and number. Keywords:- Forced convection, Baffles, Finite volume method, Simple, Quick, k- I. INTRODUCTION In recent years, a large number of experimental and numerical works were performed on turbulent forced convection in heat exchangers with different type of baffles [1-4]. This interest is due to the various industrial applications of this type of configuration such as cooling of nuclear power plants and aircraft engine ... etc. S. . V Patankar and EM Sparrow [1] have applied a numerical solution procedure in order to treat the problem of fluid flow and heat transfer in fully developed heat exchangers. These one was equipped by isothermal plate placed transversely to the direction of flow. They found that the flow field is characterized by strong recirculation zones caused by solid plates. They concluded that the Nusselt number depends strongly on the Reynolds number, and it is higher in the case of fully developed then that of laminar flow regime. Demartini et al [2] conducted numerical and experimental studies of turbulent flow inside a rectangular channel containing two rectangular baffles. The numerical results were in good agreement with those obtained by experiment. They noted that the baffles play an important role in the dynamic exchangers studied. Indeed, regions of high pressure 'recirculation regions' are formed nearly to chicanes. Recently, Nasiruddin and Siddiqui [3] studied numerically effects of baffles on forced convection flow in a heat exchanger. The effects of size and inclination angle of baffles were detailed. They considered three different arrangements of baffles. They found that increasing the size of the vertical baffle substantially improves the Nusselt number. However, the pressure loss is also important. For the case of inclined baffles, they found that the Nusselt number is maximum for angles of inclination directed downstream of the baffle, with a minimum of pressure loss. More recently, Saim et al [4] presented a numerical study of the dynamic behavior of turbulent air flow in horizontal channel with transverse baffles. They adapted numerical finite volume method based on the SIMPLE algorithm and chose

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International Journal of Engineering Research and Development

e-ISSN: 2278-067X, p-ISSN: 2278-800X, www.ijerd.com

Volume 8, Issue 12 (October 2013), PP. 06-18

6

Numerical modelling of heat transfer in a

channel with transverse baffles

M.A. Louhibi1, N. Salhi

1, H. Bouali

1, S. Louhibi

2

1Laboratoire de Mécanique et Energétique, Faculté des Sciences, BP. 717 Boulevard Mohamed VI -

60000 Oujda, Maroc. 2Ecole National des sciences Appliquées, Boulevard Mohamed VI - 60000 Oujda, Maroc.

Abstract:- In this work, forced convection heat t ransfer inside a channel o f

rectangular sec tion, containing some rectangular baffle p lates , is numerica lly

analyzed. We have developed a numer ica l model based on a fini te -volume method ,

and we have so lved the coupling pressure -veloci ty by the SIMPLE a lgori thm [6] . We

show the e ffects o f var ious parameters o f the baff les, such as, baf f le ’s he ight ,

loca tion and number on the i sotherms, s tream l ines, tempera tures distr ibutions and

loca l Nusse lt number va lues. I t i s concluded tha t: I ) The baff les loca tion and he ight

has a meaningful e ffec t on i sotherms, streamlines and to ta l hea t t ransfer through the

channel . ( I I ) The heat t ransfer enhances wi t h increas ing bo th baff le ’s height and

number.

Keywords:- Forced convect ion, Baff les, Finite volume method, Simple, Quick, k-

I. INTRODUCTION In recent years, a large number o f exper imental and numerical works were

per formed on turbulent forced convect i on in heat exchangers wi th di fferent type of

baff les [1 -4] . This interes t i s due to the var ious industr ial appl icat ions of this type

of configurat ion such as cooling of nuclear power plants and aircraf t engine . . . e tc .

S. . V Patankar and EM Sparrow [1] ha ve appl ied a numer ica l solution procedure in

order to treat the problem of f luid flo w and heat t ransfer in ful ly developed heat

exchangers. These one was equipped by iso thermal plate p laced transversely to the

direc t ion of flo w. They found tha t the f low f i e ld i s character ized by s trong

recircula t ion zones caused by so lid pla tes. They concluded that the Nussel t number

depends strongly on the Reynolds number, and i t i s higher in the case o f ful ly

developed then tha t o f laminar flo w regime.

Demar tini et a l [ 2] conducted numer ica l and experimenta l stud ies o f turbulent

f low ins ide a rec tangular channel conta ining two rectangular baff les. The numerical

result s were in good agreement wi th those obta ined by experiment. They no ted that

the baff les p lay an impor tant role in the dynamic exchangers studied. Indeed,

regions o f high pressure 'rec irculat ion regions ' a re formed near ly to chicanes .

Recent ly, Nasiruddin and Sidd iqui [3] s tudied numerical ly e ffects of baff les on

forced convection f low in a heat exchanger . The effects o f s ize and incl ina tion angle

of baff les were de ta i led . They considered three di fferent arrangements o f baffles .

They found that increas ing the s ize o f the ver t ical baffle substantial ly improves the

Nusse lt number . Ho wever , the pressure loss i s a l so impor tant . For the case o f

incl ined baff les, they found tha t the Nusselt number is maximum for angles of

incl ina tion d irected do wnstream of the baff le , with a minimum of pressure loss.

More recent ly, Sa im e t al [4] presented a numerical study of t he dynamic behavior

of turbulent air flo w in hor izonta l channel with transverse baff les. They adapted

numerical f ini te volume method based on the SIMPLE a lgori thm and chose

Numerical modell ing of heat transfer in a channel with…

7

model fo r treatment o f turbulence. Resul t s obtained for a case o f such type, a t

low Reynolds number, were presented in te rms of ve loci ty and temperature f ields.

They found the exis tence of rela t ively strong recircula t ion zones near the baffles .

The eddy zones a re responsib le o f local var iat ions in the Nusse lt s numbers along the

baff les and wal ls .

We kno w that the pr imary heat exchanger goal is to e ff ic ient ly transfer heat

from one f luid to ano ther separa ted, in most pract ical cases, by so lid wal l . To

increase heat t ransfer , severa l approaches have been proposed. We can c i te the

spec i fic treatment o f so lid separa t ion sur face ( roughness, tube winding, vibrat ion,

etc . ) . This transfer can also be improved by creation of longi tudina l vort ices in the

channel . These eddies are produced by introducing one or more transverse barr ier s

(baffle plates) ins ide the channel . The formation of these vort ices downstream of

baff les causes recirculat ion zones capable o f rap id and eff icient heat t ransfer

between sol id wal ls a nd f luid f low. I t i s this approach that we wi l l fol lo w in this

study. Indeed, we are interested in this work on the numerical model ing of dynamic

and thermal behavior o f turbulent forced convection in hor izontal channel where two

wal ls are raised to a high temperature. This channel may contain one or severa l

rectangular baff les.

A spec ia l inte rest i s given to the influence of di fferent parameters, such as height ,

number and baffle posit ions on heat t ransfer and f luid f lo w.

II. MATHEMATICAL FORMULATION The geometry of the p roblem is shown schematica l ly in Figure 1 . I t i s a

rectangular duc t wi th isothermal hor izonta l wal ls , crossed by a sta t ionary turbulen t

f low. The physica l propert ies are considered to be constants.

Figure 1: The studied channel

At each point o f the f low the ve loc ity has components (u, v) in the x and y

direc t ions, and the temperature i s denoted T . The turbulence model ing i s handled by

the c lass ical model (k - ) . k is the turbulent kinet ic energy and the viscous

diss ipat ion of turbul ence.

The Transpor t equat ions (continuity, momentum, temperature, turbulent

kinet ic energy and d iss ipat ion of turbulence) governing the sys tem, are wr it ten in

the fo l lo wing genera l fo rm :

)1()()(

S

y

y

x

x

y

v

x

u

Where ρ is the densi ty of the fluid passing

through the channel and ɸ, F φ and Sφ are given by:

Equat ions S

Cont inui té 1 0 0

Quant i té de

mouvement selon x

u t

x

P

Numerical modell ing of heat transfer in a channel with…

8

Quant i té de

mouvement selon y

v t

y

P

Energie to tale T

T

t

0

Energie cinét ique

turbulente

k

k

t

G .

Dissipa tion turbulente

t

kC

GC

)

(

2

1

With :

222

22y

u

x

v

y

v

x

uG t µ and µ t represent , respec tively,

the dynamic and turbulent viscosit ies.

2

.k

Ct

The constants used in the turbule nce model (k -Ɛ) Are those adopted by

Chieng and Launder (1980) [8] :

C 1C 2C T k

0 ,09 1,44 1,92 0,9 1 1 ,3

Boundary condit ions :

At the channel inle t :

inUu ; 0v and inTT

2/32 1,0005,0 kandUk in

At sol id wal ls :

0 vu ; 0k inw TTTand

At the channel exit s:

The gradient o f any quanti ty, wi th respec t to the longitud ina l direc t ion x is

nul .

Our goal is to determine veloc ity and temperature f ields, as well as the

turbulence parameters. Par t icular a t tent ion i s given to the quant i ficat ion parameters

ref lect ing hea t exc hanges such as the Nussel t number ( local and average) .

III. NUMERICAL FORMULATION The computer code that we have developed i s based on the fini te volume

method. Computat ional domain i s d ivided into a number o f s t i tches. To choose the

number of cel l s used in t his s tudy, we per formed several simula tions on a channel

(wi th or wi thout baffles) . F inal ly, we have op ted for a 210 × 90 meshes .

The mesh d imensions are var iab les; they t ighten a t the sol id walls

ne ighborhoods. Consequently, the s t i tch density i s higher near the hot wal ls and

baff les.

We consider a mesh having dimensions ∆x and ∆y. In the middle o f each

volume we consider the points P , ca l led centers o f control vo lumes. E , W, N, S are

Numerical modell ing of heat transfer in a channel with…

9

the centers o f the adjacent contro l vo lumes. We also consider centers, EE; WW, NN,

SS. The faces o f each cont rol vo lume are denoted e, w, n, s .

Figure 2: Mesh with P at center

By integrat ing the transport equation (1) o f ɸ on the contro l volume , we find,

a relat ion to the x direct ion:

P

we

we

S

dx

d

dx

duu

Où P

S is the source term.

One no te uF , the convect ion f low and xD / , the di ffus ion

coefficient . And wi th taking :

wwee uFuF ;

wwee xDxD /;/

And : WPwPEe dd ;

We found :

P

WPwPEewwee

S

DDFF

)()( To est imate ɸ on the faces " e "

and " w " we opted for the c lassical quick scheme [5] which i s a quadrat ic forms

using three nodes. The choice o f these nodes i s dictated by the direc t ion of f low on

these faces )00( uoru .

Fina lly, the transpor t equation (1) i s d iscre t ized on the mesh wi th P at center as :

)2(P

EEEEWWWWEEWW

PP

S

aaaa

a

With :

PEEEWWWP

eeEE

wweeeeeE

wwWW

wweewwwW

Saaaaa

Fa

FFFDa

Fa

FFFDa

)1(8

1

)1(8

1)1(

8

6

8

38

1

)1(8

3

8

1

8

6

Where : 00,01 eee FouFsiou

00,01 www FouFsiou

Numerical modell ing of heat transfer in a channel with…

10

The same thing i s done for the ver t ical "y" direct ion, using the faces "n" and

"s" and by introducing the Quick diagram nodes N, NN, S and SS.

i f convection flo w and di ffusion coefficient o f the sides "e" , "w" , "s" , "n" are

kno wn And espec ia l ly the source term P

S , the solution of equation (2) t hen gives

us the va lues of ɸ in di fferent P nodes .

One notes that to acce lerate the convergence of equation (2) we have introduced a

relaxat ion fac tor :

)3(1 0

PPP

EEEEWWWWEEWWP

P

aS

aaaaa

Where 0

P is the va lue of P in the

previous step .

The source term appears especia l ly in the conservat ion of momentum

equat ions in the fo rm of a pressure gradient which i s in pr inc iple unkno wn . To get

around this coupling we have chosen to use in our code the "Simple" algori thm

developed by Pantankar [7] . The bas ic idea of this algor i thm is to assume a f ie ld o f

ini t ia l pressure and inject i t in to the equat ions o f conserva tion of momentum. Then

we solve the sys tem to f ind a f ield o f intermediate speed (which i s not fa ir because

the pressure isn t . ) The continuity equat ion i s t ransformed into a pressure correct ion

equat ion. This las t i s de termined to find a pressure correc tion that wi l l injec t a

new pressure in the equations o f motion. The cycle i s repeated as many t imes as

necessary unti l a pressure correct ion equal "zero" corresponding to the a lgori thm

convergence. In the end we solve the transport equations o f T , k and Ɛ.

In this approach, a problem is encountered . I t is known as the checkerboard

problem.

The r i sk i s that a pressure field can be highly d isturbed by the sensed

formula tion which comprises per forming a l inear interpolat ion for es t imate the

pressure value on the facets o f the cont rol volume. To circumvent this problem we

use the so -ca lled s taggered gr ids proposed by Har low and Welch [6] . In thi s

technique, a f ir st gr id p ressure (and other scalar quanti t ies T , k and Ɛ ) is p laced in

the center o f the con trol vo lume. While o ther staggered gr ids are adopted for the

ve loc ity components u and v ( see Figure 3) .

Figure 3: Shi fted mesh

The sca lar var iables, including pressure, are stored a t the nodes (I , J ) . Each

node (I , J ) i s sur rounded by nodes E, W, S and N. The horizonta l velocity component

u i s sto red on faces "e" and "w", whi le the ver t ica l component v is stored on the

faces denoted "n" and "s" .

So the control vo lume for pressure and o ther scalar quant i t ies T , k and Ɛ is

),();1,();1,1();,1( jijijiji

Numerical modell ing of heat transfer in a channel with…

11

For component u cont rol vo lume is

),1();1,1();1,();,( jIjIjIjI .

Whi le for the v component we use : )1,1();,();,1();1,1( JiJiJiJi .

By integra t ing the conservat ion momentum equation in the horizontal direc t ion on

the volume ),1();1,1();1,();,( jIjIjIjI , we found :

)(),(),1(

)4(

1

,,

jjnbnb

JiJi

yyJIPJIPua

ua

Where :

NNNNNNSSSSSS

EEEEEEWWWWWWnbnb

uauauaua

uauauauaua

The coefficients anb are

determined by the quick scheme ment ioned above.

Simi lar ly, the integrat ion of conservat ion mo mentum equat ion in the ver t ical

direc t ion on the volume

)1,1();,();,1();1,1( JiJiJiJi , gives us :

)(),()1,(

)5(

1

,,

iinbnb

jIjI

xxJIPJIPva

va

One considers pr imar i ly an ini t ia l pressure field P*. The provisional so lution

of the equat ions (4) and (5) wi l l be denoted u* and v

*. We note that u

* and v

* doesn’t

checks the continuity equati on, and:

)6()(),(),1( 1

**

*

,*

,

ayyJIPJIP

ua

ua

jj

nbnb

JiJi

)6()(),()1,( 1

**

*

,*

,

bxxJIPJIP

va

va

ii

nbnb

jIjI

At this stage any one of the three var iables i s correct . They require correction :

)7(

'

'

'

*

*

*

vvv

uuu

PPp

Injec t ing (7) in equations (4) , (5) and (6) we find :

)8()(),('),1('

'

'

1

,,

ayyJIPJIP

ua

ua

jj

nbnb

JiJi

)8()(),(')1,('

'

'

1

,,

bxxJIPJIP

va

va

ii

nbnb

jIjI

Numerical modell ing of heat transfer in a channel with…

12

At this leve l , an approximation i s in troduced. In order to l inear ize the

equat ions (8) , the terms nbnbua ' and nbnbva ' are s imply neglected .

Normally these terms must cancel a t the procedure convergence . That i s to

say that this omission does not a ffec t the f ina l result . Ho wever , the convergence

rate is changed by this simpl i ficat ion. I t turns out that the correct ion P ' i s

overest imated by the Simple algor i thm and the ca lculat ion tends to diverge. The

remedy to s tab il ize the calculat ions i s to use a re laxa tion fac tor .

We Note that a fur ther trea tment of these te rms i s proposed in the so -cal led

algori thms "SIMPLER" and "SIMPLEC" [7] .

The equations (8) become:

)9(),('),1('' , aJIPJIPdu JiJi

)9(),(')1,('' , bJIPJIPdv jIjI

Avec :

Ji

jj

Jia

yyd

1et

Ij

ii

jIa

xxd

1

With :

Ji

jj

Jia

yyd

1 and

Ij

ii

jIa

xxd

1

Equat ions (9) give the correc tions to app ly on veloc it ies through the formulas

(7) . We have therefore :

)10(),('),1('

,*

,

aJIPJIPd

uu

Ji

JiJi

)10(),(')1,('

,*

,

bJIPJIPd

vv

jI

jIjI

Now the discret ized contin ui ty equat ion on the control vo lume of scalar quanti t ies i s

wr i t ten as fol lows :

0)()(

)()(

,1,

,,1

jIjI

JiJi

vAvA

uAuA

Where an are the s ize o f the corresponding faces .

The introduction of the veloc ity correct ion equations (10) in the continui ty

equat ion gives a fina l equat ion al lowing us to de termine the scope of pressure

correc tions P:

)11()1,('')1,(''

),1(''

),1(''),(''

11

1

1

JIPaJIPa

JIPa

JIPaJIPa

JIJI

JI

JIJI

The a lgori thm can be summarized as fo l lows : one sta r t s fro m an ini t ial

f ield**** ,, andvuP , wi th represents the sca lar quan ti t ies T, k and Ɛ. Then the

sys tem (6) is so lved to have new values o f ** vandu .

Then the sys tem (11) i s solved for the correc tions f ield pressure P '.

Thereaf ter , pressure and veloc ity are corrected by equat ions (7) and (10) to have P ,

u and v.

Numerical modell ing of heat transfer in a channel with…

13

We solve the fo l lo wing transport equation of sca lar quanti t ies (2) , ɸ = T, K

and Ɛ .

Finally, we consider :

**** ;;; vvuuPP .

And the cyc le i s repeated unti l convergence.

IV. RESULTS AND DISCUSSIONS The dimensions o f the channel presented in this work are based on

experimental data published by Demart ini et a l [2] . The air flo w is carr ied out under

the fo l lo wing condi t ions .

Channel length: 𝐿 = 0 .554 m ;

Channel diameter D = 0.146 𝑚 ;

baffle he ight : 0 <ℎ <0 1. 𝑚 ;

baff le thickness: δ = 0 .01 𝑚 ;

Reynolds number : 𝑅𝑒 = 8 .73 104

;

The hydrodynamic and thermal boundary condit ions are given by :

At the channel inle t :

inuu =7,8m/s;

0v ; inTT =300 K

On the channel walls:

0 vu and KTT w 373

At the channel exit the sys tem is assumed to be ful ly developed, ie :

0

x

Tx

vx

u

Fir s t , we compared the s truc ture o f streamlines and i so therms in a channel

wi thout baff le wi th those ob ta ined when we int roduce baffle having a height h =

0.05 m (Case 2 -1) a t the absc ise 𝐿 1 = 0 .218 𝑚 . Indeed, in figures 4 and 5 we present

streamlines and i so therms for two configurat ions.

These result s c lear ly show the impor tance of p resence of baff le (act ing as a

cooling f in) . Indeed the baff le increases heat t ransfer between the wal l an d the

f luid . This increase is caused by rec irculat ion zones do wnstream of the baff le .

(a)

(b)

Figure 4: s t reamlines: (a ) case 1 ; (b) case 2 -1

(a)

(b)

Figure 5: Iso therms: (a) case 1 ; (b) case 2 -1

Numerical modell ing of heat transfer in a channel with…

14

We then s tudied the inf luence of baff le he ight on flo w s tructure and hea t

t ransfer . We chose the heights (h = 0 .05 m; cases 2 -1) h = 0 , 073 𝑚 (Case 2 -2) and h

= 0, 1 𝑚 (case 2 -3) .

The figures 6 and 7 present streamlines and i sotherms for a channel containing baff le

wi th di fferent he ights .

(a)

(b)

Figure 6: streamlines : (a ) case 2 -2 ; (b) case 2 -3

(a)

(b)

Figure 7: Iso therms: (a) case 2 -2; (b) case 2 -3

I t is c lear that the i sotherms are more condensed near baff le , as and when the

he ight h increases. This ind icates an increase o f heat t ransfer near baffle . Indeed, the

increase in h expanded exchange area be tween f luid and walls . In add it ion, when h

increases , the recircula t ion zone beco mes increas ingly impor tant ( see Figures 4 (b)

and figures 6 (a) and (b)) . This causes an acce lerat ion of f low, which improves hea t

t ransfer wi thin the channel .

We present figures 8 and 9 in order to iden t i fy the influence of h on

ve loc it ies and temperature p rofi les a long y at x = 0 .45 from channel inlet . Four

va lues o f h are considered.

Figure 8: Hor izontal velocity Profi les along y at x = 0.45 « inf luence of h »

Figure 9: Temperature p rof i les along y at x = 0.45 m « inf luence of h »

Numerical modell ing of heat transfer in a channel with…

15

These resul ts al low us to conclude that the increase o f baffle he ight has two

contrad ic tory effects. I t is t rue tha t there i s substant ial increase in heat exchange

(appearance of recircula t ion zones most co mmon), but the re is a lso a loss o f pressure

( f low b lockage) .

In the purpose of measur ing the influence of 'h ' on loca l heat t ransfer , we

have presented in figure 10, the local Nusse lt number a long the channel for the four

cases o f h considered. I t sho ws tha t upstream of the baff le (x <0.2 m) curves are

confused , whi le , just af ter baffle locat ion, effec t o f baff le he ight on Nussel t

number beco me increas ingly impor tant away from the baffles .

0

50

100

150

0 0.2 0.4 0.6

Nu Cas 21

Nu Cas 22

Figure 10 : Local number Nu along the channel « inf luence of h »

We then s tudied the inf luence of baff les number and posi t ion 'F igure 11 and 12 '.

(a)

(b)

(c)

Figure 11 : S treamlines : (a) cas 3 -1; (b) cas 3 -2; (c) cas 3 -3

We consider two baffles of same height h = 0.08 m. The fir s t baff le i s pl aced

at the distance 𝐿1 = 0 .15 𝑚 , whi le the second is posi t ioned at the d istance d 1 = 0 .05

m from the f irs t (case 3 -1) , d 1 = 0 .10 m (case 3 -2) and d 1 = 0 .15 m (case 3 -3) . We

note the existence of two rec irculat ion zones downstream of the f ir st baff le . Also the

f irs t recircula t ion zone 'defined by baffles ' becomes increas ingly important , which

contr ibute to an increase in heat t ransfer in this area, as sho wn in Figure 12. Indeed,

when the baff les are c lose to each o ther 'd 1 small ' , the fluid i s blocked in the

chimney del imi ted by x = L 1 and x = L1 + d 1 . This reduces the f low speed at tha t

Numerical modell ing of heat transfer in a channel with…

16

loca tion and thus there wi l l be a decrease in the heat t ransfer in this a rea. Or when

d 1 increases, the f luid has suff ic ient space to move rap idly, hence hea t t ransfer

increases in this zone 'see figure15 ' .

(a)

(b)

(c)

Figure 12 : Iso therms

(a) : « cas 3 -1 » ; (b) : « cas 3 -2 » ; (c) « cas 3 -3 »

In the fol lo wing figures 13 and 14, we compare the profi le o f hor izonta l

ve loc ity and tempera ture dis tr ibution. Calculat ion i s done on t he y-axis at x = 0 .45

m from the channel inlet for three di fferent baff les spac ing. We find that more

spac ing i s impor tant more heat exchange i s impor tant in areas l imi ted by two

baff les.

Figure 13 :Prof i les o f the horizonta l ve loc ity a t x = 0.45 m « Influence of the

spac ing be tween two baff les »

Figure 14: Prof i les o f the total tempera ture at x = 0.45 m « Inf luence of the spacing

between two baffles »

Numerical modell ing of heat transfer in a channel with…

17

Figure 15 present the loca l Nusse lt number along the channel fo r three

considered spacing d 1 = 0 .05m, 0 .1m and 0 .15m.

Figure 15 :Local Nusse l t number along the channel « Influence of baff les number

and posit ion »

We dist ingue two areas :

The fir s t def ined by 0 <x <0.3m whi le the second by x> 0.3m. For the fir st

region, an increase in nu mber of baffles improves the hea t t ransfer ; whereas the

reverse is t rue for the second zone.

We chooses to show the inf luence of baff les number on hea t t ransfer along

the channel for three cases : Channel wi thout baff les, channel containing a s ingle

baff le and channel conta ining two baffles 'Figure 16 '.

I t should be noted tha t genera l ly, hea t t ransfer i s proport iona l to baff les

number. Indeed, the Nussel t number character izing hea t t ransfer wi thin the channel

increases wi th increasing baffles number.

Figure 16: Local Nusse lt number a long the channel

V. CONCLUSION The thermal behavior o f a stat ionary turbulent forced convection f low wi thin

a baff led channel was ana lyzed . The result s show the ab il i ty o f our code to predict

dynamic and thermal f ields in var iou s geometr ic si tuat ions. We stud ied mainly the

inf luence of baff les he ight and spac ing on heat t ransfer and f luid f low. One can

conclude tha t:

1 - Increase in the baffle he ight improves heat t ransfer between channel wall s

and fluid passing through i t ;

2 - Heat t ransfer becomes increasingly impor tant wi th adding baffles .

3 - The spacing d 1 be tween baff les has di fferent e ffec ts on loca l heat

t ransfer . Any t ime d 1 has no t a lo t of inf luence on the overal l hea t t ransfer in the

channel .

In perspec tive , we inten d deepen and c lar i fy our result s . Indeed, we wi l l adapt our

code to others geometr ic cases (non -rec tangular baffles or baffles inc lined) . Fina lly,

we wi l l a l so try to re fine more the turbulence model .

Numerical modell ing of heat transfer in a channel with…

18

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[2] . L.C.DEMARTNI, H.A.VIELMO and S.V.MOLLER, « Numerica l and

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[6] . F. Harlo w; J . Welsh ; « Staggered gr id », Numerical calcula t ion of t ime

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[7] . Patankar , S.V. (1980) , «Numer ica l Heat Transfer and Fluid Flow»,

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