“STUDY OF HELICAL HELICA L COIL HEAT EXCHANGER AND COMPARE IT WITH STRAIGHT TUBE HEAT EXCHANGER”
A project !"#$tte% to
B&$'($ I)t$t!te O* Tec&)o'o+,- D!r+ C.G. For t&e p(rt$(' *!'*$''#e)t o* t&e (/(r% o* %e+ree o*
BACHELOR OF ENGINEERING I)
MECHANICAL ENGINEERING 0No1e#"er2Dece#"er 0No1e#"er2Dece#"er 34567
Project G!$%e% B,8
S!"#$tte% B,8
Mr.Yo+e& 9!#(r
A"&$jeet De/()+()
0A$t()t Pro*eor7
Aj(, S$)+& R(&!' Y(%(1 R(1$)%r( 9!#(r
DECLARATION BY THE CANDIDATE
I the undersigned solemnly declare that the report the project work entitled “St!%, O* He'$ He '$c( c('' Co$' Co$' He He(t (t E:c& E:c&() ()+e +err ()% ()% co#p co#p(r (ree $t /$t /$t& Str( Str($+ $+&t &t T!"e He He(t (t E:c&()+er” $s based on our work carried out during the course of our study under the
supervision of Mr. Yo+e& 9!#(r.(Assistant professor) I assert that the statements made and conclusions drawn are an outcome of our research work. We further declare that to the best of our knowledge and belief the report does not contain any part of work which has been submitted for the award of B.. degree in !.".#.$. %.
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DECLARATION BY THE CANDIDATE
I the undersigned solemnly declare that the report the project work entitled “St!%, O* He'$ He '$c( c('' Co$' Co$' He He(t (t E:c& E:c&() ()+e +err ()% ()% co#p co#p(r (ree $t /$t /$t& Str( Str($+ $+&t &t T!"e He He(t (t E:c&()+er” $s based on our work carried out during the course of our study under the
supervision of Mr. Yo+e& 9!#(r.(Assistant professor) I assert that the statements made and conclusions drawn are an outcome of our research work. We further declare that to the best of our knowledge and belief the report does not contain any part of work which has been submitted for the award of B.. degree in !.".#.$. %.
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CERTFICATE OF THE SUPER
$his is to certify that the work incorporated in the project “St!%, O* He'$c(' Co$' He(t E:c&()+er ()% Co#p(re $t /$t& Str($+&t T!"e He(t E:c&()+er” is a record
of research work carried out by&&&&&&&&&&&&&&&&&of mechanical branch under my guidance guidance and supervision supervision for the award of 'egree of Bachelor of ngineering ngineering in the faculty of Mr.Y !hhattisg isgarh arh "wami "wami #iveka ivekanan nand d $echni echnical cal Mr.Yo o+e& 9!#(r of !hhatt %niversity Bhilai (!..) India. $o the best of my knowledge and belief the thesis i) ii) iii) iii)
mbodies th the wo work of th the ca candidate hi himself *as dully been completed +ulfi +ulfill llss the the re,ui re,uirem rement entss of the the ord ordin inan ance ce rela relatin ting g to the the B B degr degree ee of of the the
iv) iv)
%niversity and Is up up to the the desir desired ed sta stand ndard ard both both in in resp respect ect of con conten tents ts and and lan langu guag agee for for being referred to the e-aminers.
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"ignature
"ignature
roject uide
rof. 'r "./. A0%12
3r 2ogesh 2ogesh /umar "ahu
*ead of 'epartment
(Assistant rofessor )
3echanical ngineering
CERTIFICATE BY THE EXAMINER
“St!%, %, o* He He'$ '$c( c('' Co$' Co$' He He(t (t $his $his is to certi certify fy that that the the proj projec ectt work work entit entitled led“St! E:c&()+e E:c&()+err ()% Co#p(re Co#p(re $t /$t& Str($+&t Str($+&t T!"e T!"e He(t e:c&()+er” e:c&()+er” "ubmitted by
&&&&&&&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&&&&&&&&& && has been e-amined by the undersigned as a part of the e-am e-amin inati ation on for for the the award award of Bach Bachel elor or of ngi ngine neeri ering ng degr degree ee in 3ech 3echan anica icall ngineering in the Bhilai Institute of $echnology $echnology'urg. 'urg.
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"ignature
"ignature
Internal -aminer
-ternal -aminer
'ate4
'ate4
AC9NOWLEDGEMENT
Working on this project has been a great learning e-perience for us. $here were moments of an-iety when we could not solve for several days and there were moments when we could solve a problem after struggling for several days. But we have enjoyed every bit of process and are thankful to all people associated with us during this period.We also owe our gratitude to respected principal Dr. Ar!) Aror( who blessed us with this e-tra ordinary knowledge and e-perience regarding our project. *e also provided us all the necessary facilities to complete our project. We would like to e-press deep gratitude to respected Pro*. Dr S.9.G()+!', ( *.5.' of 3echanical ngineering 'epartment) for his helpful solutions and comments enriched by e-perience which improved our ideas for betterment of project. We owe a great debit of our gratitude for his constant advice cooperation and encouragement throughout the project. $he progress of our project STUDY OF HELICAL COIL HEAT EXCHANGER AND COMPARE IT WITH STRAIGHT TUBE HEAT EXCHANGER could not
have been achieved without the kind support of our project guide Mr Yo+e& 9!#(r S(&!(Assistant professor of 3echanical ngineering 'epartment).
It will be our pleasure to acknowledge utmost co6operation and valuable suggestions from time to time given by staff of 3echanical ngineering 'epartment to whom we owe our entire computer knowledge and also we would like to thank all those persons who have directly or indirectly helped us by providing books and the computer peripherals and other necessary amenities which helped in the development of this project which would otherwise not been possible. At last we would like to progress our sincere thanks to all authors for joining insight into the working of complete description of the project. We would like to also thank all those persons who directly or indirectly helped us by sharing their knowledge and e-perience as it might become an impossible task to complete our project without their help and guidance.
TABLE OF CONTENT
i) ii) iii) iv)
v)
AB"$7A!$8888888888888888(i) 1I"$ 5+ +I%78888888888888...(ii) 1I"$ 5+ ABB7#A$I50 A0' "23B51888.(iii) !*A$7 9) I0$75'%!$I508888888888888969: ;) 1I$7$%7 7#IW88888888889<69= :) 75B13 I'0$I+I!A$I508888888.9>6;? <) 3$*5'5152888888888888..;96;@ ) !$' 7"%1$" C 'I"!%""I50888..;=6;> D) !50!1%"I50 C "!5 5+ +%$%7 W57/...:?6:9 BIB1I57A*288888888888888
ABSTRACT
*eat e-change is an important unit operation that contributes to efficiency and safety of many processes. All the heat e-changers can be operated in both parallel6 and counter6flow configurations. $he heat e-change is performed between hot and cold water. *eat e-changer is important appliance in field of thermal heat mass fluid flow as in nuclear reactor steam power plant (in super heater)fertiliEers factoryetc. In this project basic heat e-changers types have been studied and basic operations and phenomena it works upon "pecial emphasis has been laid upon study of helical coil heat e-changer designing the assembly of helical coil heat e-changer . !omparing it straight tube heat e-changer numerically and theoretically with its advantage over straight tube heat e-changer its advantage is proved by secondary flow phenomena 13$'( logarithmic mean temperature difference) using nusselt and prandtl number considering fouling and other parameters.
0$7 LIST OF FIGURE
+ig. 9.9
arallel flow 88888888888888888888
+ig. 9.;
!ounter flow88888888888888888888..
+ig. 9.:
*eat transfer C $emperature distribution in counter concurrent and concurrent flow888888888..
+ig. 9.<
!ross flow888888888888888888888.
+ig. 9.
"hell and tube heat e-changer 8888888888888..
+ig. 9.D
3ultiple shell and tube heat e-changer8888888888..
+ig. 9.@
*elical *eat -changer 888888888888888...
+ig. 9.=
helical coil888888888888888888888...
+ig. 9.>
"econdary flow in helical coil88888888888888.
+ig. 9.9? $he fouling resistance as a function of time for all runs8888. +ig. .9 5verall *eat 7esistance8888888888888888.. +ig. .; "ection view of *eat -changer8888888888888.
0$$7 LIST OF ABBRE
F
fluid density kgGm
:
μ
fluid viscousity at mean bulk temperature kgGmh
μ w
fluid viscousity at pipe wall temperature kgGmh
x
thickness of coil wall m
#f
volume available for flow in annulus area m
#c
volume occupied by 0 turns of coil m
#a
volume occupied by annulus m
U
5verall heat transfer coefficient kcalGhm ;H!
u
fluid viscousity mGh
:
:
:
∆t im
1og6mean temperature difference H!
∆t c
corrected log6mean temperature difference H!
Rt
$ube side fouling factor hm ;H!Gkcal
Ra
"hell side fouling factor hm ;H!Gkcal
r
Average radius of helical coil taken from the centre line to the centre line coilm
q
#olumetric flowerate of fluid m :Gh
Q
*eat load kcalGh
Re
7eynold number 'u G μ or 'G μ dimensionless
Pr
randtl number , c p µ/k dimensionless
n
Actual number ot turns of coil needed for a given process heat duty( N rounded
N
theoretical number of turns of coil
mc
mass flow rate of cold fluid kgGh
mh
mass flow rate of hot fluid kgGh
L
1ength of the coil needed to form N turns m
k c
$hermal conductivity of coil wall kcalGhm ;H!
k
$hermal conductivity of fluid kcalGhm ;H!
j*
!olbourn factor for heat transfer ( h D/k )( Pr )69G: ( µ/µw)6?.9< dimensionless i
ho
*eat transfer coefficient outside coil kcalGhm;H!
hio
*eat transfer coefficient inside coiled tube based on outside diameter of coil kcalGhm ;
hic
*eat transfer coefficient inside coiled tube ( hi corrected for coil) based on inside diameter of coil kcalGhm ;H!
hi
*eat transfer coefficient inside straight tube tube based on inside diameter ;
kcalGhm H!
H
*eight of cylinder m
Gs
3ass velocity of fluid
D H&
5utside diameter of heli- m
D H)
& m/! " /#$% ' (& $'D H&&' D H)& $$* kgG m;h
5utside diameter of heli- m
D H
Average diameter of heli- m
De
"hell side e,uivalent diameter of coil m
Di
Inside diameter of coil m
Do
5utside diameter of coil m
c p
+luid heat capacity kcalGkg H!
(
5utside diameter of inner cylinder m
%
Inside diameter of inner cylinder m
+
& Area of cross6section of coil " /#$D m;
+a
& Area of fluid flow in annulus " /#$% ' (& $'D H&&' D H)& $$ m;
+
Area of heat transfer m ;
5. INTRODUCTION
5. INTRODUCTION
*eat e-changers are off6the6shelf e,uipment targeted to the efficient transfer of heat from a hot fluid flow to a cold fluid flow in most cases through an intermediate metallic wall and without moving parts. *eat e-changer is the process e,uipment designed for effective transfer of heat energy between two fluids a hot fluid and coolant .*eat e-changers serve a straightforward purpose 4controlling a systemJs or substanceJs temperature by adding or removing thermal energy. Although there are many different siEes levels of sophistication and types of heat e-changers they all use a thermally conducting elementKusually in the form of a tube or plateKto separate two fluids such that one can transfer thermal energy to the other. *eat losses or gains of a whole heat e-changer with the environment can be neglected in comparison with the heat flow between both fluid flows i.e. a heat e-changer can be assumed globally adiabatic. $hermal inertia of a heat e-changer is often negligible too (e-cept in special cases when a massive porous solid is used as intermediate medium) and steady state can be assumed reducing the generic energy balance to4 openings
openings ΔE =W + Q + ∑ h dm
- . mh) 0 m h& time
te
e
time t where the total enthalpy h t has been appro-imated by enthalpy (i.e. negligible mechanical energy against thermal energy) and means output minus input. C'($*$c(t$o) &e(t e:c&()+er to #eet 1(r,$)+ (pp'$c(t$o) . 57 O) t&e "($ o* oper(t$)+ pr$)c$p'e (7 D$rect co)t(ct &e(t e:c&()+er
$he energy transfer between hot and cold fluid is brought about by their complete physical mi-ing 4 there is simultaneous transfer of heat and mass. -4 water cooling tower. "7 Re+e)er(tor &e(t e:c&()+er
$he hot fluid is passed through certain medium called matri- .$he heat is transferred to the solid matri- and accumulates there. $he heat thus stored in heated matri-is subse,uently transferred to the cold fluid by allowing it to pass over aheated matri-.
c) Rec!per(tor In recuperator the fluid flow either side of a separating wall the heat transfer occur between the stream without mi-ing or physical contact between each other. 37 O) t&e "($ o* (rr()+e#e)t o* &e(t *'o/ (7T&e P(r(''e' F'o/ He(t E:c&()+er
A double pipe heat e-changer can be operated in parallel flow mode as shown in the diagram at the left. "imilarly a shell and tube heat e-changer can be operated in appro-imately parallel flow by having both fluids enter at one end and e-it at the other end. With parallel flow the temperature difference between the two fluids is large at the entrance end but it becomes small at the e-it end as the two fluid temperatures approach each other. $he overall measure of heat transfer driving force the log mean temperature difference is greater for counter flow so the heat e-changer surface area re,uirement will be larger than for a counter flow heat e-changer with the same inlet and outlet temperatures for the hot and the cold fluid.
F$+.5.5 P(r(''e' F'o/
F$+.5.3 Co!)ter F'o/
T&e Co!)ter*'o/ He(t E:c&()+er
A counterflow heat e-changer has the hot fluid entering at one end of the heat e-changer flow path and the cold fluid entering at the other end of the flow path. !ounter flow is the most common type of li,uid6li,uid heat e-changer because it is the most efficient. A double pipe heat e-changer is usually operated as a counter flow heat e-changer as shown in the diagram at the left. $he flow pattern in a shell and tube heat e-changer with a single tube pass will be appro-imately counterflow if it is long in comparison with its diameter. Because of the baffles and the need to distribute
the flow of the shell side fluid over the cross6section of the shell the flow is not as close to counterflow in a shell and tube heat e-changer as it is in a double pipe heat e-changer. $he bottom diagram on the left shows appro-imately counter flow in a straight tube one tube pass shell and tube heat e-changer.
He(t tr()*er = Te#per(t!re %$tr$"!t$o) $) co!)terco)c!rre)t ()% co)c!rre)t *'o/ F$+ 5.6
"7 Cro *'o/ &e(t e:c&()+er
In the cross flow arrangement the hot and cold fluid are directed at right angle to each other. $he hot fluid flow inside separate tube and itJs mi-.
F$+.5.> Cro *'o/
67 O) t&e "($ o* #ec&()$c(' %e$+) o* &e(t e:c&()+er
!oncentric tubes heat e-changer
different stream do not
$wo concentric pipes are used each carrying one of the fluids .$he direction of flow may correspond to counter flow or unidirectional arrangement
(. S&e'' ()% t!"e &e(t e:c&()+er
5ne of the fluid carried through a bundle of tubes enclosed by shell. $he other fluid is forced through the shell and flows over the outside surface of the tubes.$he direction of flow for either or both fluid may change during its passage through the heat e-changer.
F$+.5.? S&e'' ()% t!"e &e(t e:c&()+er
". M!'t$p'e &e'' ()% t!"e &e(t e:c&()+er
$he two fluid may flow through the e-changer only once one or both the fluid may traverse the e-changer more than once.
F$+.5.@ M!'t$p'e &e'' ()% t!"e &e(t e:c&()+er
*eat e-changer s are one of the most important process e,uipmentJs that are used in all industries such as petroleum gas petrochemical power plants food and etc. $he aim of using heat e-changers in processes is to reduce energy consumption. "hell and tube hea t e-changers are the commonest and most used ones. Although shell and tube heat e-changer have lower thermal efficiency than compact e-changers With the increase in cost of harnessing energy and limited sources of energy there is need for efficient utiliEation of waste energy so there is need for more efficient heat e-changer *elical heat e-changer are considered as modern technology which are designed and used to fulfil the shortcoming of common heat e-changer A helical heat e-changer consist of helical coil fabricated out of meatal pipe that is fitted in the annular portion of two concentric cylinder.
F$+.5. He'$c(' He(t E:c&()+er
In helical coils the radial velocity component generated from the centrifugal force results in secondary flow. A pair of generally symmetrical vortices in the vapour core affecting the main fluid stream is produced as depicted in figure 9.9 $he main differences in heat transfer and fluid flow characteristics between helical coils and straight tube are related to this secondary flow effect caused by centrifugal forces. $he li,uid droplets are pushed from the inner tube wall to the outer tube wall through the center of the tube then li,uid moves to the inner wall due to pressure difference between the outer and inner surfaces. $his phenomenon improves the heat transfer and retards the dry out and prevents stratification in helical coils compared to straight tubes as proved for large tube diameters
F$+.5. He'$c(' Co$'
F$+.5. Seco)%(r, *'o/ He'$c(' Co$'
When a fluid flows through a straight tube the fluid velocity is ma-imum at the tube center Eero at the tube wall C symmetrically distributed about the a-is. *owever when the fluid flows through a curved tube the primary velocity profile indicated above is distorted by the addition of secondary flow pattern. $he secondary flow is generated by centrifugal action and acts in a plane perpendicular to the primary flow. "ince the velocity is ma-imum at the center the fluid at the center is subjected to the ma-imum centrifugal action which pushes the fluid towards the outer wall. $he fluid at the outer wall moves in ward along the tube wall to replace the fluid ejected outwards. $his results in the formation of two vortices symmetrical about a horiEontal plane through the tube center.It has been found that the effect of coil curvature is to suppress turbulent fluctuations arising in the flowing fluid and smoothing the emergence of turbulence. $hus it increases the value of the 7eynolds number re,uired to attain a fully turbulent flow as compared to that of a stra ight pipe. $he above effect of turbulent fluctuations suppression enhances as the curvature ratio increases. Another important phenomena observed in helical tubes is the relamianriEation. $he fluid flow which was originally turbulent changes to laminar while flowing inside a helical pipe.
FOULING
+ouling is generally defined as the deposition and accumulation of unwanted materials such as scale algae suspended solids and insoluble salts on the internal or e-ternal surfaces of processing e,uipment including boilers and heat e-changers. *eat e-changers are process e,uipment in which heat is continuously or semi6continuously transferred from a hot to a cold fluid directly or indirectly through a heat transfer surface that separates the two fluids. *eat e-changers consist primarily of bundles of pipes tubes or plate coils +ouling on process e,uipment surfaces can have a significant negative impact on the operational efficiency of the unit. 5n most industries today a major economic drain may be caused by fouling. About 9L of the maintenance costs of a process plant can be attributed to heat e-changers and boilers and of this half is probably caused by fouling. +ouling in heat e-changers is not a
new problem. In fact fouling has been recognised for a long time and research on heat e-changer fouling was conducted as early as 9>9? and the first practical application of this research was implemented in the 9>;?Js.3ajor detrimental effects of fouling include loss of heat transfer as indicated by charge outlet temperature decrease and pressure drop increase. 5ther detrimental effects of fouling may also
include blocked process pipes under6deposit corrosion and pollution. Where the heat flu- is high as in steam generators fouling can lead to local hot spots resulting ultimately in mechanical failure of the heat transfer surface. "uch effects lead in most cases to production losses and increased maintenance costs. 1oss of heat transfer and subse,uent charge outlet temperature decrease is a result of the low thermal conductivity of the fouling layer or layers which is generally lower than the thermal conductivity of the fluids or conduction wall. As a result of this lower thermal conductivity the overall thermal resistance to heat transfer is increased and the effectiveness and thermal efficiency of heat e-changers are reduced. A simple way to monitor a heat transfer system is to plot the outlet temperature versus time. In one unit at an oil refinery fouling led to a feed temperature decrease from ;9?H! to 9@?H!. In order to bring the feed to the re,uired temperature the heat duty of the furnace may have to be increased with additional fuel re,uired and resulting increased fuel cost. Alternatively the heat e-changer surface area may have to be increased with conse,uent additional installation and maintenance costs. $he re,uired e-cess surface area may vary between 9?6?L with an average around :L and the additional e-tra costs involved may add up to a staggering ;. to :.? times the initial purchase price of the heat e-changers. With the onset of fouling and the conse,uent build up of fouling layer or layers the cross sectional area of tubes or flow channels is reduced. In addition increased surface roughness due to fouling will increase frictional resistance to flow. "uch effects inevitably lead to an increase in the pressure drop across the heat e-changer which is re,uired to maintain the flow rate through the e-changer and may even lead to flow blocks. +ouling is responsible for the emission of many millions of tonnes of carbon dio-ide as well as the use and disposal of haEardous cleaning chemicals. $he factors that govern fouling in heat e-changers are many and varied. 5f such factors some may be related to the feed properties such as its chemical nature density viscosity diffusivity pour and cloud points interfacial properties and colloidal stability factors. Based on the different physical and chemical processes involved it is convenient to classify the fouling main types as4 52 Prec$p$t(t$o) Fo!'$)+8 !rystalliEation of dissolved salts due to solubility changes
with temperature and subse,uent precipitation onto the heat transfer surface. "caling belongs also to this type of fouling M9=6;?N.
32 P(rt$c!'(te Fo!'$)+8 'eposition of suspended particles in the process stream onto
the heat transfer surfaces M9:69DN. $his process includes sedimentation where settling occurs under gravitational forces. 62 B$o'o+$c(' Fo!'$)+ "$o*o!'$)+8 $his type occurs in raw water due to the
attachment and growth of macroorganisms andGor their products on the heat transfer surfaces >2 C&e#$c(' Re(ct$o) Fo!'$)+8 Is a result of chemical reactions between reactants in
the flowing fluid in which the surface material itself is not a reactant (e.g. in petroleum refining. polymer production and food processing). ?2 Corro$o) Fo!'$)+8 'ue to chemical or electrochemical reaction between the heat
transfer surface itself and the fluid stream to produce corrosion products which in turn change the surface thermal characteristics and foul it. @2 So'$%$*$c(t$o) Fo!'$)+8 'ue to freeEing of a pure li,uid or a higher melting point
components of a multi6component solution onto a cooler surface. Fo!'$)+ re$t()ce 8
$he fouling resistance 7 is determined by subtracting the fouling resistance when the test section is clean (at time Eero) from that when fouled
__ Where, Uc and U are the overall heat transfer coecients for clean and fouling conditions respectively. These coecients are calculated from the general heat transfer equation ,
and,
is the logarithmic mean temperature dierence,
As mentioned before, the most common and widely practically eisting fouling type is the !asymptotic! mode. This type of fouling can be described by an eponential equation as,
Where, "#f is the asymptotic fouling resistance. $m%&'W( tc is the time constant, hr
The percentage reduction in U due to fouling is given by,
%ombining with equation $)( yields,
The change in asymptotic fouling resistance determined .
can be also
F$+. 5.54. T&e *o!'$)+ re$t()ce ( ( *!)ct$o) o* t$#e *or ('' r!).
Fo!'$)+ #$t$+(t$o)- co)tro' ()% re#o1('
In order to prevent or mitigate the impact of fouling problems various steps can be taken during plant design and construction and also during plant operation and maintenance. +ouling mitigation and control re,uire scientific considerations in design and construction. In general high turbulence absence of stagnant areas uniform fluid flow and smooth surfaces reduce fouling and the need for fre,uent cleaning. In addition designers of heat e-changers must consider the effects of fouling upon heat e-changer performance during the desired operational lifetime of the heat e-changers. $he factors that need to be considered in the designs include the e-tra surface re,uired to ensure that the heat e-changers will meet process specifications up to shutdown for cleaning the additional pressure drop e-pected due to fouling and the choice of appropriate construction materials. fouling is e-pected on the tube side some engineers recommend using larger diameter tubes (a minimum of ; mm 5') M;DN. $he use of corrugated tubes has been shown to be beneficial in minimising the effects of at least two of the common types of fouling. !orrosion6type fouling can also be minimised by the choice of a construction material which does not readily corrode or produce voluminous deposits of corrosion products. 3ounting the heat e-changer vertically can minimise the effect of deposition fouling as gravity would tend to pull the particles out of the heat e-changer away from the heat transfer surface even at low velocity levels.
He'$c('', co$'e% e:c&()+er o**er cert($) (%1()t(+e.
9) !ompact siEe provides a distinct benefit. *igher film coefficientsKthe rate at which heat is transferred through a wall from one fluid to another and more effective use of available pressure drop result in efficient and less6e-pensive designs. ;) $rue counter6current flow fully utiliEes available 13$' (logarithmic mean temperature difference). *elical geometry permits handling of high temperatures and e-treme temperature differentials without high induced stresses or costly e-pansion joints. :) *igh6pressure capability and the ability to fully clean the service6fluid flow area add to the e-changerJs advantages. <)
!oils give better heat transfer performance since they have lower wall resistance
C higher process side coefficient. )
A coil can provide a large surface area in a relatively small reactor volume.
D$(%1()t(+e o* &e'$c(' co$'e% &e(t e:c&()+er 9) 'ensely packed coils can create unmi-ed regions by interfering with fluid flow.
;) !leaning of vessels with coils becomes much difficult. APPLICATIONS Ue o* &e'$c(' co$' *or &e(t tr()*er (pp'$c(t$o)8
9)*elical coils are used for transferring heat in chemical reactors and agitated vessels because heat transfer coefficients are higher in helical coils. $his is especially important when chemical reactions have high heats of reaction are carried out and the heat generated (or consumed)has to be transferred rapidly to maintain the temperature of thereaction. Also because helical coils have a compact configuration more heat transfer surface can be provided per unit of space than by the use of straight tubes. ;) Because of the compact configuration of helical coils they can be readily used in heat transfer application with space limitations for e-ample in steam generations in marine and industrial applications. :) $he e-istence of self induce radial acceleration field in helical coils makes helical coils most desirable for heat transfer and fluid flow applications in the absence of gravity field such as for space ships in outer space .<) *elical coiled tubes have been and are used e-tensively in cryogenic industry for the li,uefaction of gases.
3.LITERATURE RE
3.LITERATURE RE
A heat e-changer is a straightforward device which is utiliEed to move heat from one place to another using an evaporation6condensation cycle. *eat pipes are referred to as the OsuperconductorsO of heat due to their ,uick transfer capability with minimal heat loss .$he whole entire process only makes use of : major components which are the container the working fluid inside the pipe and the thermosyphon effect also called the capillary structure. But before studying the specific information of just how the heat pipe works it is best to know the history of heat pipe technology to get a solid OfeelO of its mechanism and how it differs from other comparable devices. Pr$)c$p(' %$**ere)ce "et/ee) &e(t tr()*er $) '(#$)(r *'o/ ()% t&(t $) t!r"!'e)t *'o/8
$he principal difference between laminar and turbulent flow as far as heat transfer is concerned is that an additional mechanism of heat transfer in the radial and aEimuthal directions becomes available in turbulent flow. $his is commonly termed Peddy transportQ and is intense providing much better transfer of energy across the flow at a given a-ial position than in laminar flow wherein conduction is typically the only mechanism that operates in the transverse directions (an e-ception occurs when there are secondary flows in the transverse direction such as in coiled tubes). Another difference worthwhile noting is the e-tent of the Pthermal entrance regionQ in which the transverse temperature distribution becomes Pfully developed.Q $his region is relatively short in turbulent flow (precisely because of the intense turbulent transverse transport of energy) whereas it tends to be long in laminar flow. *eat transfer correlations based on e-perimental results are typically divided into those applicable in the thermal entrance region and those that apply in the Pfully developedQ region. In the case of laminar flow it is important to be aware of this distinction and normally a laminar flow heat e-changer is designed to be short to take advantage of relatively high heat transfer rates that are achievable in the thermal entrance region. In the case of turbulent flow the thermal entrance region is short as noted earlier and typically heat transfer occurs mostly in the Pfully developedQ region. $herefore turbulent heat transfer correlations are commonly provided for the latter region
T&e *o''o/$)+ ree(rc& /or &( "ee) %o)e 2 T$#ot&, . Re))$e- <$j(,( G.S. R(+&(1() 5 *ave done An e-perimental study of a double6pipe helical heat e-changer. $wo heat e-changer siEes and both parallel flow and counter flow configurations were tested. +low rates in the inner tube and in the annulus were varied and temperature data recorded. 5verall heat transfer coefficients were calculated and heat transfer coefficients in the inner tube and the annulus were determined using Wilson plots. 0usselt numbers were calculated for the inner tube and the annulus. $he inner 0usselt number was compared to the literature values. $hough the boundary conditions were different a reasonable comparison was found. $he 0usselt number in the annulus was compared to the numerical data. D. G. Pr("&()j()- G. S. <. R(+"(1() ()% T. . 9e))$c 3 H(1e %o)e e:per$#e)t(' t!%, to determine the relative advantage of using a helically coiled heat e-changer versus a straight tube heat e-changer for heating li,uids. $he particular difference in this study compared to other similar studies was the boundary conditions for the helical coil. 3ost studies focus on constant wall temperature or constant heat flu- whereas in this study it was a fluid6to6fluid heat e-changer. All tests were performed in the transitional and turbulent regimes. H. S&oo!&#()%- M.R. S('$#po!r- M.A. A&(1()2Be&("(%$ 6 *ave done an e-perimental investigation of the shell and helically coiled tube heat e-changers. $hree heat e-changers with different coil pitches and curvature ratios were tested for both parallel6flow and counter6flow configurations. All the re,uired parameters like inlet and outlet temperatures of tube6 side and shell6side fluids flow rate of fluids etc. were measured using appropriate instruments. 5verall heat transfer coefficients of the heat e-changers were calculated using Wilson plots. $he inner 0usselt numbers were compared to the values e-isted in open literature. N(er G&or"()$- He(# T(&er$()- Mo*$% Gorj$- He(# M$r+o'"("(e$ >- *ave done an e-perimental investigation of the mi-ed convection heat transfer in a coil6in6shell heat e-changer is reported for various 7eynolds and 7ayleigh numbers various tube6to6coil diameter ratios and dimensionless coil pitch. $he purpose of this article is to check the influence of the tube diameter coil pitch shell6side and tube6side mass flow rate over the performance coefficient and modified effectiveness of vertical helical coiled tube heat e-changers. $he calculations have been performed for the steady6state and the e-periments were conducted for both laminar and turbulent flow inside coil. It was found that the mass flow rate of tube6 side to shell6side ratio was effective on the a-ial temperature profiles of heat e-changer 6N$() C&e)- $2T$() H()- T$e)2C&$e) e)- L$ S&(o - We)2/e) C&e) ? *ave done an e-perimental investigation on condensation heat transfer of 769:
condensation heat transfer coefficients of the helical section are
and outermost diameters of the spiral6coil are ;@?.?? and - -perimental data and !+' simulations using fluent D.:.;D are used to developed improved heat transfer coefficient correlation for the flue gas side of heat e-changer. 3athematical model is developed to analyEe the data obtained from !+' and e-perimental results to account for the effects of different functional dependent variables tube diameter and coil diameter which effect the heat transfer. 5ptimiEation is done using numerical techni,ues. P($(r) N(p&o) 5?- has studied the thermal performance and pressure drop of the helical6coil heat e-changer with and without helical crimped fins. $he heat e-changer consists of a shell and helically coiled tube unit with two different coil diameters. ach coil is fabricated by bending a >.? mm diameter straight copper tube into a helical6coil tube of thirteen turns. !old and hot water are used as working fluids in shell side and tube side respectively. $he e-periment done at the cold and hot water mass flow rates ranging between ?.9? and ?.;; kgGs and between ?.?; and ?.9; kgGs respectively. $he inlet temperatures of cold and hot water are between 9 and ; H! and between : and < H! respectively. $he effects of the inlet conditions of both working fluids flowing through the test section on theheat transfer characteristics discussed
6.PROBLEM IDENTIFICATION
6.PROBLEM IDENTIFICATION
*eat e-changer is the process e,uipment designed for effective transfer of heat energy between two fluids a hot fluid and coolant .*eat e-changers serve a straightforward purpose 4controlling a systemJs or substanceJs temperature by adding or removing thermal energy. $he main objective of this research is to determine the heat transfer characteristics of a helical heat e-changer both numerically and e-perimentally and to determine the effects of heat e-changer geometry and fluid properties on the heat transfer characteristics. $o accomplish this goal the following problems were encountered4 9. #arious parameters changing due to coil shape temperature gradient and various thermodynamic properties. ;. roblems in determining overall heat transfer coefficient due to fouling and other parameters. :. 'esign and construction of a physical model of the heat e-changer. <. $esting of the physical model under different flow rates and flow configurations (parallel flow and counter flow). . !omparison of the results from both theoretical and e-perimental work.
>.METHODOLOGY
>.METHODOLOGY *eat -changer is a very efficient device in which e-change of heat between two fluids takes place one fluid is hot while another is cold. *eat e-changers are widely used in various industries such as power plants automobiles cryogenic industries chemical reactors etc. *elical coil heat e-changers also got vary vast applications in modern industries as compare to straight tube heat e-changers .*ere we are going to discuss about the heat transfer coefficient of *elical coil heat e-changers 1etting the cold and hot fluid flow through heat e-changer coil then by virtue of temperature difference hot fluid will transfer heat to cold fluid therefore this rate of heat transfer can be calculated by below e,uation
Where
U U overall heat transfer coefficient + U heat e-changer area V
1 m U average temperature difference between the fluids
B($c t!%, o* ter#$)o'o+$e re'(te% to ("o1e eK!(t$o) O1er('' He(t Tr()*er Coe**$c$e)t
$he overall heat transfer coefficient represents the total resistance to heat transfer from one fluid to another. $he functional form of
U or the product U+ may be
derived for any particular geometry by performing a standard conduction analysis on the system of interest. $o illustrate this consider first a planar wall of thickness 1 subject to convection on both sides.
F$+.?.5 O1er('' He(t Re$t()ce
Where % is the O1er('' He(t Tr()*er Coe**$c$e)t LMTD8$he 'o+ #e() te#per(t!re %$**ere)ce (also known by its initialism LMTD)
is used to determine the temperature driving force for heat transfer in flow systems most notably in heat e-changers. $he 13$' is a logarithmic average of the temperature difference between the hot and cold streams at each end of the e-changer .$he 13$' represents the effective average temperature difference between the two heat transfer fluids over the length of the heat e-changer and though derived here for parallel flow formula is also valid for counter flow heat e-changers. If we assume parallel flow the steady state heat transferred through a differential area
2+ is
88888888(?9)
Where the subscripts PhQ and PcQ denote the hot and cold fluids respectively. We have already seen that we can write the heat transfer across this differential area in terms of the 5verall *eat $ransfer !oefficient as
+rom ,uation ?9
8888888888(?;)
such that
"ubstitute for
from ,uation ?;
8..8.8(?:)
Assuming all terms on the right hand side of ,uation ?: are constant we can integrate from point (9) to point (;) along the length of the heat e-changer
888888.888.8(?<) We further take advantage of the fact
such that
"ubstituting into ,uation ?<
and rearranging gives
where
is called the 1og 3ean $emperature 'ifference (13$'). "imple procedure for designing helical heat e-changer are $o calculate &e(t tr()*er coe**$c$e)t in the coil parameter must be known 9.$he length of coil needed to make 0 turns 4
L. N 3 &"r )& 0p& $
(9)
;.$he volume occupied by coil
4 c ."/#$Do& L
(;)
:.$he volume of annulus
4 a ."/#$% &'(& $pN
(:)
<.$he volume available for the flow of fluid in annulus
4 . 4 a '4
(<)
$he shell side e,uivalent diameter 'eU <#f G'o; 1
()
and the annulus following
+ig6.; "chematic cutway of helical heat e-changer
D.$he heat transfer coefficient in the annulus h can be calculated using one of the following two e,uations for 7eynolds numbers Re in the range of ?69???? , (D) M:N is recommended
ho De /k U?.D Re?. Pr ?.:9
(D)
+or 7e over 9????,(@)M
ho De /k.-567Re-588 Pr )/6µ/µw $-5)# (@) $he heat transfer coefficient of fluid flowing inside the coil h io can be determined using conventional methods such as described in 7ef M
hio . hicD /D i o $
(=)
x.Do' D $/& ) i $he overall heat transfer coefficient%is given by
)/U.)/ ho 0)/ hio0x/ k c 0 Rt 0 Ra (>)
'etermine the re,uired area6$he area needed for heat transfer is given by
+.Q/∆t c
(9?)
$he log6mean6temperature6differenceYtlmmust be corrected to take into account the fact that the fluids are flowing perpendicular to each otherwhich is done by standard correction factor for perpendicular flowM
?.EXPECTED RESULT = DISCUSSION
?.EXPECTED RESULTS = DISCUSSION
+rom the e-periment we can determine that the *elical coil heat e-changer is found to be more effective as compare to straight tube heat e-changer. heat transfer coefficient of *elical !oil *eat -changer is comparatively greater than straight tube heat e-changer. $here is effect of curvature on the flow of fluids which causes a secondry flow due to centrifugal force so the heat transfer between two fluids takes place in the efficient manner thatJs why *elical coil heat e-changer has high effectiveness compare to straight tube heat e-changer
@.CONCLUSION = SCOPE OF FUTURE WOR9
@.CONCLUSION = SCOPE OF FUTURE WOR9
#arious research work has been carried out in the past regarding to effectiveness of helical coiled heat e-changer and also form this e-periment it is found that the helical coil heat e-changer may be a great option for effective heat transfer between two fluids in the modern industries where it may incorporated in the place of straight tube heat e-changer . In present "cenario there is need for more efficient and compact heat e-changer .helical coil heat e-changer may be a suitable solution for more efficient heat transfer .helical coil heat e-changer may also be incorporated with the fins which increases the heat transfer rate and also can improve the effectiveness of helical coiled heat e-changer
BIBLIOGRAPHY
BIBLIOGRAPHY
9. '."./umar
Heat an2 9a:: 1ran:er @ th revised edition pg6D=;6D=< "./. /ataria
C "ons ;. 7./. 7ajput
1herma;
:. 0A ./ Heat an2 9a:: 1ran:er :rd edition $ata 3cgraw6*ill publication < '.". /umar >;ui2 9echanic: an2 >;ui2 Power
Heat an2 9a:: 1ran:er
D. Z..*olman , Heat tran:er 3craw *ill Book !ompany @ Acharya 0. "en 3. and *. !. !hang. ;??9. Analysis of heat transfe enhancement in coiled6tube heat e-changers. ?nternationa; @ourna; o Heat an2 9a:: 1ran:er #ol. <<4 :9=>6:9>> =. Akiyama 3. and /. !. !heng. 9>@;. 1aminar forced convection heat transfer in curved pipes with uniform wall temperature. ?nternationa; @ourna; o Heat an2 9a:: 1ran:er #ol. 949<;D69<:9.. >. Berger ". A. $albot 1. and 1. ". 2ao. 9>=:. +low in curved pipes. +nn5 ReA5>;ui29ech5 #ol. 94@? p. 9<. 99. 0oble 3.A. /amlani Z.". and 3c/etta Z.Z. *eat $ransfer in "piral !oils Petro;eum ; p. @;:. 9<. P*eliflow !oolers and *eatersQ Bulletin *6=<6: raham 3anufacturing !o. Inc. 9. P*eliflow *eat -changersQ Bulletin **6:? raham 3anufacturing
