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INTRODUCTION:

Heat exchangers are devices that provide the flow of thermal energy between two or more

fluid streams at different temperatures. The fluids are separated by a solid wall so that they

never mix, or directly contacted. They have generally no external heat and work interactions.

Typical applications are heating or cooling of a fluid stream and evaporation or condensation

of a single or multicomponant fluid streams. Other applications are sterilization, pateurization,

distillation, cyristallization or controlling a process fluid. They are widely used in

refrigeration, air conditioning,space heating, electricity generationand chemical processing.

Heat Exchanger Classification :

The classification of heat exchangers is based on the basic operation, construction, heat

transfer, and flow arrangements, due to the large number of configurations of heat

exchangers. This classification as outlined by Kakac and iu !"##$% willbe discussed&

'ecuperators and regenerators

Transfer processes& direct contact or indirect contact

(eometry of construction& tubes, plates, and extended surfaces

Heat transfer mechanisms& single phase or two phase flow )low *rrangement& parallel flow, counter flow, or cross flow

+n this proect, + studied on the shell and tube heat exchangers.The shell and tube heat

exchanger is a class of heat exchanger designs. *s its name implies this type of heat

exchanger consists of a shell !a large tube% with a series of small tubes inside it. Two fluids

with different initial temperatures flow through the exchanger. One through the tubes and the

other through the shell. Heat is transferred from one fluid to the other.This is a great way forconservation of energy.

-hell and tube heat exchangers are employed when a process reuires large uantities of

fluid to be heated or cooled. /ue to their compact design, these heat exchangers contain a

large amount of heat transfer area and also provide a high degree of heat transfer efficiency.

They are commonly used as oil coolers, power condensers, preheaters and steam generators in

both fossil fuel and nuclear0based energy production applications, and also used in the air

conditioning and refrigeration industry.

"
http://en.wikipedia.org/wiki/Refrigerationhttp://en.wikipedia.org/wiki/Air_conditioninghttp://en.wikipedia.org/wiki/Space_heatinghttp://en.wikipedia.org/wiki/Electricity_generationhttp://en.wikipedia.org/wiki/Refrigerationhttp://en.wikipedia.org/wiki/Air_conditioninghttp://en.wikipedia.org/wiki/Space_heatinghttp://en.wikipedia.org/wiki/Electricity_generation


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There can be many variations on the shell and tube design. 1ost are either one, two or four

pass designs. This refers to the number of times the fluid in the tubes passes through the fluid

in the shell. +n a single pass heat exchanger, the fluid goes in one end and out the other. Two

and four pass designs are common because the fluid can enter and exit on the same side. This

makes construction much simpler.

*ccording to flow types of fluid through,they can be classified into two maor sections. +n

parallel0flow heat exchangers, the two fluids enter the exchanger at one end, and flow through

in the same direction and leave together at the other end while in counter0flow heat

exchangers the fluids enter the exchanger from opposite ends. The counter current design is

most efficient since they allow the highest log mean temperature difference between the hot

and cold streams. 1any companies however do not use them because they can break easily in

addition to being more expensive to build. Often multiple heat exchangers can be used to

simulate the counter current flow of a single large exchanger.

)igure.".shell and tube exchanger

2


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2. PARAMETER AND CA!CU!ATION

*ssumptions&

3egligible heat transfer from surroundings

3o heat generation within the system

4onstant properties

3o stored energy

3egligible kinetic and potential enery changes

3o phase change

Ta"le #. $i%en Para&eters

567 8thylene glycol 9ater1ass flow rate mh, mc !kg:s% 6,7;< calculated

Temperature in Ti, ti !K% 6=6,"; 2#$,";

Temperature out To, to !K% 6"6,"; 6"$,";

-pecific Heat, 4ph, 4pc !:kg K% 2#62 >"$7

/ynamic ?iscosity @ !3 s:m2% 7,777;=< 7,777#7=

Thermal 4onductivity k !9:m K% 7,>$< 7,>

4o!B:3 m% 7,7777777>>

-f 7,";

Kf !":year% 7,2

9u !kg:h% "26>=,7

Hy !hour:year% =777

Ta"le ). Design Para&eters

+nside diameter of the tube, +/ !m% 7,722

Outside diameter of the tube O/ !m% 7,72>

+nside shell diameter !+/shell % !m% 7,%G3t F7,726#>$6.7 2

ID

nLGfP ttt

= F 6,##6#>>6=6 Ca

The pressure drop of return losses, MCr&

22;." tr VnP =

?tFmc:!pG*c%F 7,2 m:s

22;." tr VnP = F "$7,,


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2.. Calc(lation of hell i*e Heat Transfer Coefficient+ ho:

*fter calculating tube side values, shell side calculations must be done. )irst step of this

calculation is euivalent diameter.

8uivalent diameter, /e, for a suare pitch&

OD

ODPD Te

.

%>:!> 22

= F 7,726=>$6 m

4learance between the tubes, 4&

4FCt0O/F 7,77


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MT"F Ti0to

MT2F To0ti

TiF 6=6,"; K ToF 6"6,"; K tiF 2#$,"; K toF 6"$,"; K

NTlmF 67,=$"76 m K:9

!oGO/%F 62,


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3umber of passes 2

3umber of tubes 2";"


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+n this study number of tubes is main design parameter. *ccording to )igure.2 hi decreases

when number of tubes increases. hi depends on 'eynolds number and 'eynolds and it

changes with different tube numbers. Therefore, changing number of tubes affects the hi value

inversely proportional.

ho vs Nt

0

500

1000

1500

2000

2500

60 61 62 63 64 65 66

Nt

ho ho (W/m 2K)

)igure.6.ho versus 3t graph

This graph shows that ho value is constant with increasing number of tubes because the

parameters that affect the ho value does not depend on tube number.

Uo vs Nt

1352

1354

1356

1358

1360

1362

1364

1366

1368

1370

1372

60 61 62 63 64 65 66

Nt

Uo Uo

)igure.>.o versus 3t graph

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)igure > indicates the relation between o and 3t. o decreases while 3t increases

according to this plot. o is directly related on hi and ho values. Decause of the fact that hi

decreases and ho remains constant with increasing 3t, an increase in o value is observed.

P vs Nt

170

175

180

185

190

195

200

60 61 62 63 64 65 66

Nt

P P (Pa)

)igure.;. MC versus 3t graph

Total pressure drop euals to summation of pressure drop of return losses and tube side

pressure drop. Cressure drop of return losses is related with the velocity of tube side and tube

side pressure drop depends on tube side 'eynold number and length. /uring the optimization

tube side velocity remains constant whereas 'eynold number and length decrease with

increasing tube number. *s a result, total pressure drop inversely proportional with tube

number as it is seen in )igure ;.

""


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Ao(m 2)

18,5

18,55

18,6

18,65

18,7

18,75

60 61 62 63 64 65 66

Nt

Ao Ao(m 2)

)igure.>7,>7

B:year when the the tube number is


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of cost, 8o and *o are the most significant parameters. /uring optimization *o value arises

as in )igure < and 8o decreases as in the calculations. p to the optimum 3t value, decreasing

in the 8o is much more effective than increasing in the *o.However, after this optimum point,

opposite situation is valid. Therefore, cost is decrasing upto optimum tube number value and

after this value an increase is observed for cost.

,.CONC!UION

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)or this heat exchanger design, carbon steel is selected due to its low cost and higher

thermal conductivity. 8xcept from carbon steel, the other materials can be used for the desired

stainless properties. +n addition, " shell 2 tube pass heat exchanger type and suare pitch are

assumed.

+n calculations, the tube number range between


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http&::www.the0engineering0page.com

http&::www.cheresources.com:designexzz.html

http&::en.wikipedia.org:wiki:-hellandtubeheatexchanger

).C. +ncropera, /.C. /ewitt, T.. Dergman, *.-. avine, )undamentals of Heat and

1ass Transfer.

4. 4aputo, C. 1. Celagagge, C. -alini, Heat exchanger design based on economic

optimisation, *pplied Thermal 8ngineering. 277=

";
http://www.the-engineering-page.com/http://www.cheresources.com/designexzz.htmlhttp://en.wikipedia.org/wiki/Shell_and_tube_heat_exchangerhttp://www.the-engineering-page.com/http://www.cheresources.com/designexzz.htmlhttp://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger

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