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Ministry of Higher Education

King Soud University

College of Engineering

Chemical Engineering Department

Research Title-:

Shell and Tube

Heat Exchanger

ame!" Moh#d Saad $almood

o%!" &'()*&++,

Dr%!" Male- .l .hmed

Sub/ect !" ChE 0)0 11 Heat Transfer 22

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3ntroduction"!

A shell and tube heat exchangeris a class of heat exchanger designs. It is the most

common type of heat exchanger in oil refineries and other large chemical processes,and is suited for higher-pressure and higher-temperature applications. As its name

implies, this type of heat exchanger consists of a shell (a large pressure vessel) ith a

!undle of tu!es inside it. "ne fluid runs through the tu!es, and another fluid flos

over the tu!es (through the shell) to transfer heat !eteen the to fluids. The set of

tu!es is called a tu!e !undle, and may !e composed !y several types of tu!es: plain,

longitudinally finned, etc.

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A heat exchanger is a device for transferring heat from one fluid to another, here a

solid all separates the fluids so that they never mix. They are idely used in

refrigeration, air conditioning, space heating, poer production, and chemical

processing. "ne common example of a heat exchanger is the radiator in a car, in

hich the hot radiator fluid is cooled !y the flo of air over the radiator

surface. (#)

Theory and Application:-

To fluids, of different starting temperatures, flo through the heat exchanger. "ne

flos through the tu!es (the tu!e side) and the other flos outside the tu!es !ut inside

the shell (the shell side). $eat is transferred from one fluid to the other through the

tu!e alls, either from tu!e side to shell side or vice versa. The fluids can !e either

li%uids or gases on either the shell or the tu!e side. In order to transfer heat efficiently,

a large heat transfer area should !e used, leading to the use of many tu!es. In this ay,aste heat can !e put to use. This is an efficient ay to conserve energy.

$eat exchangers ith only one phase (li%uid or gas) on each side can !e called one-

phase or single-phase heat exchangers. To-phase heat exchangers can !e used to

heat a li%uid to !oil it into a gas (vapor), sometimes called !oilers, or cool a vapor to

condense it into a li%uid (called condensers), ith the phase change usually occurring

on the shell side. &oilers in steam engine locomotives are typically large, usually

cylindrically-shaped shell-and-tu!e heat exchangers. In large poer plants ith

steam-driven tur!ines, shell-and-tu!e surface condensers are used to condense the

exhaust steam exiting the tur!ine into condensate ater hich is recycled !ac' to !e

turned into steam in the steam generator.

Shell and tube heat exchanger Types:-

There can !e many variations on the shell and tu!e design. Typically, the ends of each

tu!e are connected to plenums(sometimes called 4ater boxes) through holes in

tubesheets. The tu!es may !e straight or !ent in the shape of a , called -tu!es.

U"Tubes

The hell and Tu!e (u-tu!e) is the most common type of heat exchanger used in theprocess, petroleum, chemical and $*A+ industries, it contains a num!er of parallel u-

tu!es inside a shell. hell Tu!e heat exchangers are used hen a process re%uires

large amounts of fluid to !e heated or cooled. ue to their design, shell tu!e heat

exchangers offer a large heat transfer area and provide high heat transfer efficiency.

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In nuclear poer plants called pressuried ater reactors, large heat exchangers called

steam generators are to-phase, shell-and-tu!e heat exchangers hich typically have

-tu!es. They are used to !oil ater recycled from a surface condenser into steam to

drive the tur!ine to produce poer. ost shell-and-tu!e heat exchangers are either /,

#, or 0 pass designs on the tu!e side. This refers to the num!er of times the fluid in the

tu!es passes through the fluid in the shell. In a single pass heat exchanger, the fluid

goes in one end of each tu!e and out the other.

urface condensers in poer plants are often /-pass straight-tu!e heat exchangers.

To and four pass designs are common !ecause the fluid can enter and exit on the

same side. This ma'es construction much simpler.

Straight"Tube )"pass

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"ne pass means that the fluid enter on one side and exit on the other side of the heat

exchanger

There are often bafflesdirecting flo through the shell side so the fluid does not ta'e

a short cut through the shell side leaving ineffective lo flo volumes.

+ounter current heat exchangers are most efficient !ecause they allo the highest log

mean temperature difference !eteen the hot and cold streams. any companies

hoever do not use single pass heat exchangers !ecause they can !rea' easily in

addition to !eing more expensive to !uild. "ften multiple heat exchangers can !e used

to simulate the counter current flo of a single large exchanger.

Straight"Tube '"pass

To pass heat exchanger means that the fluid enters and exit on the same side of the

heat exchanger.

There are many different types or designs of shell and tu!e heat exchangers to meet

various process re%uirements. hell and Tu!e heat exchangers can provide steady heat

transfer !y utiliing multiple passes of one or !oth fluids. 1+ shell and tu!e heat

exchangers come in to (#) and four (0) pass models standard, and multi-pass custom

models.

hell and Tu!e heat exchangers use !affles on the shell-side fluid to accomplished

mixing or tur!ulence. 2ithout the use of !affles, the fluid can !ecome stagnant in

certain parts of the shell.

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Selection of tube material!"

To !e a!le to transfer heat ell, the tu!e material should have good thermal

conductivity. &ecause heat is transferred from a hot to a cold side through the tu!es,

there is a temperature difference through the idth of the tu!es. &ecause of the

tendency of the tu!e material to thermally expand differently at various temperatures,

thermal stresses occur during operation. This is in addition to any stress from highpressures from the fluids themselves. The tu!e material also should !e compati!le

ith !oth the shell and tu!e side fluids for long periods under the operating conditions

(temperatures, pressures, p$, etc.) to minimie deterioration such as corrosion. All of

these re%uirements call for careful selection of strong, thermally-conductive,

corrosion-resistant, high %uality tu!e materials, typically metals. 3oor choice of tu!e

material could result in a lea' through a tu!e !eteen the shell and tu!e sides causing

fluid cross-contamination and possi!ly loss of pressure. (/)

tandard heat exchangers particularly made for heavy duty ever ith medium

pressure ranges. The composition can !e made ith different choice of materials, all

sort of com!inations ma'e this type of exchangers versatile enough to solve any

pro!lem of fluids, flos, even ith high duty rating. (#)

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5affles:

3unched from steel plates, ith supporting lips for higher thermal efficiency and more

safety in case of vi!ration.

Shell 6 Tubesheets:

2elded car!on steel construction, to give most rugged exchanger, ade%uate thic'nessfor t trou!le free long life. hell side connections made also for customers

re%uirement, over the standard threaded connections e propose flanges

Ho4 To Ma-e a Shell and Tube Heat Exchanger 7 102

2hen preparing to design a heat exchanger, do

you ever onder here to start4

/.Is there a phase change involved in my

system4

A %uic' loo' at the !oiling points compared

ith the entrance and exit temperatures ill help

you anser this %uestion.

#. $o many 5ones5 are involved in my

system4

56ones5 can !est !e defined as regimes of

phase changes here the overall heat transfercoefficient (o) ill vary. sing T-7

(Temperature-$eat) diagrams are the !est ay to

pinpoint ones. The system is defined as co-

current or countercurrent and the diagram is

constructed. The diagram on the left illustrates

the use of T-7 diagrams. These diagrams should

accompany your !asic (input-output) diagram of

the heat exchanger. +hemical 8/ enters the shell

at #99 9+ as a superheated vapor. In 6one /, it

releases heat to the tu!eside chemical (+hemical

8#). 6one / ends ust a +hemical 8/ !egins tocondense. The tu!eside (+hemical 8#) enters as a

li%uid or gas and does not change phase

throughout the exchanger. +hemical 8/ leaves

6one / and enters 6one # at its !oiling

temperature, T!/. T; mar's the temperature of

+hemical 8# hen +hemical 8/ !egins to

condense. In 6one #, +hemical 8/ condenses to

completion hile +hemical 8# continues to

increase in temperature. The temperature of

+hemical 8# hen +hemical 8/ is fully

condensed is denoted at T;;.

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simply li!erating heat to +hemical 8# as it !ecomes a su!cooled li%uid and exits the

shell at /99 9+.

efining ones is one of the most important aspects of heat exchanger design. It is

also important to remem!er that if your process simulator does not support oned

analysis (such as +hemcad III), you should model each one ith a separate heat

exchanger. Thus, the previous illustration ould re%uire = heat exchangers in thesimulation. &T, do not dra = exchangers on your 3ve estimated the overall heat transfer coefficient, use

the e%uation 7FoADTlmto get your preliminary area estimate. Remem!er to use the

a!ove e%uation to get an area for each one, then add them together.

B. 2hat geometric configuration is right for my exchanger4

Go that you have an area estimate, it>s time to find a geometry that meets yourneeds. "nce you>ve selected a shell diameter, tu!esheet layout, !affle and tu!e

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spacing, etc., it>s time to chec' your velocity and pressure drop re%uirements to see if

they>re !eing met. 1xperienced designers ill usually com!ine these steps and

actually o!tain a tu!e sie that meets the velocity and pressure drop re%uirements and

then proceed. ome guidelines may !e as follos: =@0 in. and /.9 in. diameter tu!es

are the most popular and smaller sies should only !e used for exchangers needing

less than =9 m#of area. If your pressure drop re%uirements are lo, avoid using fouror more tu!e passes as this ill drastically increase your pressure drop. "nce you

have a geometry selected that meets all of your needs, it>s on to step 8H.

H. Go that I have a geometry in mind, hat is the actual overall heat transfer

coefficient4

This is here you>ll spend much of your time in designing a heat exchanger.

Although many text!oo's sho GuF9.9#C(GR1)9.B(G3R)

9.==as the 5fundamental

e%uation for tur!ulent flo heat transfer5, hat they sometimes fail to tell you is that

the exponents can vary idely for different situations.

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