PM3125 Lectures 6to9 Heat Transfer

7/25/2019 PM3125 Lectures 6to9 Heat Transfer

1/88

Prof. R. Shanthi 1

PM3125: Lectures 6 to 9

Content of Lectures 6 to 12:

Heat transfer:

-Source of heat

- Heat transfer- Stea an! e"ectricit# as heatin$ e!ia

- %eterination of reuireent of aount of

stea'e"ectrica" ener$#

- Stea (ressure- Matheatica" (ro)"es on heat transfer


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Prof. R. Shanthi 2

*hat is Heat+


3/88

Prof. R. Shanthi 3

*hat is Heat+

Heat is ener$# in transit.


4/88

Prof. R. Shanthi ,

nits of Heat /he S unit is theou"e 4

hich is eua" to 7eton-etre 74.

Historica""# heat as easure! in ters of the a)i"it#

to raise the te(erature of ater.

/he ca"orie ca"4: aount of heat nee!e! to raise the

te(erature of 1 $rae of ater )# 1 C0fro

1,.50C to 15.50C4

n in!ustr# the 8ritish thera" unit 8tu4is sti"" use!:aount of heat nee!e! to raise the te(erature of 1 ")

of ater )# 1 0fro 630 to 6,04


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Prof. R. Shanthi 5

Conersion )eteen !ifferent

units of heat:

1 ; 0.23


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Prof. R. Shanthi 6

Sensi)"e Heat

*hat is ?sensi)"e heat@+

Sensi)"e heat is associate!ith a te(erature chan$e


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Prof. R. Shanthi A

S(ecific Heat Ca(acit#

/o raise the te(erature )# 1 B !ifferentsu)stances nee! !ifferent aount of ener$# )ecause

su)stances hae !ifferent o"ecu"ar confi$urations

an! )on!in$ e$: co((er ater oo!4

/he aount of ener$# nee!e! to raise the

te(erature of 1 >$ of a su)stance )# 1 B is >non

as the s(ecific heat ca(acit#

S(ecific heat ca(acit# is !enote! )# c


8/88

Prof. R. Shanthi e!

e=a("es )# R. Shanthini

(u)"ishe! )# Science !ucation nit acu"t# of Science

niersit# of Pera!eni#a4

a"so u("oa!e! at htt(:''.rshanthini.co'PM3125.ht4


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Prof. R. Shanthi 23

*arin$ cure for ater*hat is the aount of heat reuire! to chan$e 2 >$ of ice

at -20o

C to stea at 150o

C at 2 )ar (ressure+

-20oC ice


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Prof. R. Shanthi 2,


at -20o

C to stea at 150o


-20oC ice

0oC e"tin$ (oint of ice


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Prof. R. Shanthi 25


at -20o

C to stea at 150o


-20oC ice


120.2oC )oi"in$ (oint of ater at 2 )ar

8oi"in$ (oint of ater at 1 at (ressure is

100oC.

8oi"in$ (oint of ater at 2 )ar is 120.2oC.

IRefer the Stea /a)"e.J


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Prof. R. Shanthi 26


at -20o

C to stea at 150o


-20oC ice


120.2oC )oi"in$ (oint of ater at 2 )ar

150oC su(erheate! stea

S(ecific heat

S(ecific heat

S(ecific heat

Latent heat

Latent heat


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Prof. R. Shanthi 2A


at -20o

C to stea at 150o


S(ecific heat reuire! to raise the te(erature of ice fro -20oCto 0oC

; 2 >$4 2.06 >'>$ oC4 I0 - -204JoC ;

Latent heat reuire! to turn ice into ater at 0oC

; 2 >$4 33, >'>$4 ; 66< >

S(ecific heat reuire! to raise the te(erature of ater fro 0o

C to120.2oC

; 2 >$4 ,.1< >'>$ oC4 I120.2 - 04JoC ; 100,.9 >


28/88

Prof. R. Shanthi 2$ of ice

at -20o

C to stea at 150o


Latent heat reuire! to turn ater into stea at 120.2oC an! at 2 )ar

; 2 >$4 2202 >'>$4 ; ,,0, >

ILatent heat of a(ouriEation at 2 )ar is 2202 >'>$ as cou"! )ereferre! to fro the Stea /a)"eJ

S(ecific heat reuire! to raise the te(erature of stea fro 120.2oC

to 150oC

; 2 >$4 2AA0 K 2A0A4 >'>$ ; 126 >

Intha"(# at 120.2oC an! 2 )ar is the saturate! stea entha"(# of

2A0A >'>$ an! the entha"(# at 150oC an! 2 )ar is 2AA0 >'>$ as

cou"! )e referre! to fro the Stea /a)"eJ


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Prof. R. Shanthi 29


at -20o

C to stea at 150o


/ota" aount of heat reuire!

; 66< > 100,.9 > ,,0, > 126 >

; 62


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Prof. R. Shanthi 30

(("ication: Heat =chan$ert is an in!ustria" eui(ent in hich heat is transferre! fro a hot

f"ui! a "iui! or a $as4 to a co"! f"ui! another "iui! or $as4 ithout

the to f"ui!s hain$ to i= to$ether or coe into !irect contact.

Hot f"ui!

at /Hin Hot f"ui!

at /Hout

Co"! f"ui!

at /Cout

Co"! f"ui!

at /Cin

Heat "ost )# the hot f"ui!

; Heat $aine! )# the co"! f"ui!


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Prof. R. Shanthi 31

(("ication: Heat =chan$er


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Prof. R. Shanthi 32

Heat =chan$er

hotchot/HinK /Hout4 ; co"!cco"! /CoutK /Cin4. .

Heat "ost )# the hot f"ui! ; Heat $aine! )# the co"! f"ui!

ass f"o rate

of hot f"ui!

S(ecific heatof hot f"ui!

ass f"o rate

of co"! f"ui!

S(ecific heatof co"! f"ui!

/e(erature

!ecrease in the

hot f"ui!

/e(erature

increase in the

co"! f"ui!


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Prof. R. Shanthi 33

Heat =chan$er

hotchot/HinK /Hout4 ; co"!cco"! /CoutK /Cin4. .

Heat "ost )# the hot f"ui! ; Heat $aine! )# the co"! f"ui!

/he a)oe is true on"# un!er the fo""oin$ con!itions:

14 Heat e=chan$er is e"" insu"ate! so that no heat is "ost to the

enironent

24 /here are no (hase chan$es occurrin$ ithin the heate=chan$er.


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Prof. R. Shanthi 3,

Heat =chan$er

Heat "ost )# the hot f"ui! ; Heat $aine! )# the co"! f"ui! Heat "ost to the enironent

f the heat e=chan$er is 7D/ e"" insu"ate! then

* > ! " 1 i H h


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Prof. R. Shanthi 35

Hi$h (ressure "iui! ater at 10 MPa 100 )ar4 an!

30oC enters a series of heatin$ tu)es. Su(erheate!stea at 1.5 MPa 15 )ar4 an! 200oC is s(ra#e! oer

the tu)es an! a""oe! to con!ense. /he con!ense!

stea turns into saturate! ater hich "eaes the

heat e=chan$er. /he hi$h (ressure ater is to )e

heate! u( to 1A0oC. *hat is the ass of stea

reuire! (er unit ass of incoin$ "iui! ater+

/he heat e=chan$er is assue! to )e e"" insu"ate!a!ia)atic4.

*or>e! =a("e 1 in Heat =chan$er

S " i > ! " 1 i h


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Prof. R. Shanthi 36

So"ution to *or>e! =a("e 1 in Heat =chan$er

S " i * > ! " 1 i H h !


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Prof. R. Shanthi 3A

Hi$h (ressure 100 )ar4 ater enters at 30oC an! "eaes at 19'>$ oC4 = 1A0-304oC

; 5'>$

INou cou"! ca"cu"ate the a)oe )# ta>in$ the !ifference in entha"(ies at

the 2 $ien states fro ta)"es aai"a)"e.J

So"ution to *or>e! =a("e 1 in Heat =chan$er cont!.

S " i * > ! " 1 i H h !


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Prof. R. Shanthi 3e! =a("e 1 in Heat =chan$er cont!.

S " ti t * > ! " 1 i H t h t!


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Prof. R. Shanthi 39

Since there is no heat "oss fro the heater

Heat "ost )# stea ; Heat $aine! )# hi$h (ressure aterMass f"o rate of stea = 1951 >'>$

; Mass f"o rate of ater = 5'>$

Mass f"o rate of stea ' Mass f"o rate of ater

; 5$ of ater



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Prof. R. Shanthi ,0

Oie the !esi$n of a heat e=chan$erhich has the ost effectie heat

transfer (ro(erties.

ssi$nent

@earning obEecti#es"3& To be able to appreciate heat transfer applications in pharmaceutical

industry

1& To become familiar with the wor%ing principles of #arious heateFchangers

'& To get a mental picture of different heat eFchangers so that sol#ingheat transfer problems in class becomes more interesting

* > ! " 2 i H t h


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Prof. R. Shanthi ,1

Stea enters a heat e=chan$er at 10 )ar an! 200oC an!

"eaes it as saturate! ater at the sae (ressure. ee!-

ater enters the heat e=chan$er at 25 )ar an!


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Prof. R. Shanthi ,2

- Stea enters at 10 )ar an! 200oC an! "eaes it as saturate! ater at

the sae (ressure.- Saturation te(erature of ater at 10 )ar is 1A9.9oC.

- ee!-ater enters the heat e=chan$er at 25 )ar an! $

Mass f"o of stea ' Mass f"o of fee!-ater

; 333.9< ' 2066 ; 0.161A >$ strea ' >$ of ater

So"ution to *or>e! =a("e 2 in Heat =chan$er

S " ti t * > ! " 1 i H t h t!


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Prof. R. Shanthi ,3

f the fee!-ater "eain$ the heat e=chan$er is fe! !irect"# to a

)oi"er to )e conerte! to stea at 25 )ar an! 300o

C fin! the heatreuire! )# the )oi"er (er >$ of fee!-ater.

-/e(erature of fee!-ater "eain$ the heat e=chan$er is 159.9oC-8oi"in$ (oint of ater at 25 )ar is 221.$

; 2,33 >'>$ of fee!-ater



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Prof. R. Shanthi ,,

Heat Transfer

is the means by which

energy mo#es from

a hotter obEect to

a colder obEect


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Prof. R. Shanthi ,5

9echanisms of Heat Transfer

onductionis the flow of heat by direct contact between a warmer and acooler body.

on#ectionis the flow of heat carried by mo#ing gas or li!uid.$warm air rises, gi#es up heat, cools, then falls&

Gadiationis the flow of heat without need of an inter#ening medium.

$by infrared radiation, or light&


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Prof. R. Shanthi ,6

Latent heat Con!uction

Conection

Ra!iation



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Prof. R. Shanthi ,A

Con!uction

HOT

(lots of vibration)

COLD

(not much vibration)

Heat travels

along the rod


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Prof. R. Shanthi , hain$ > ; 1.0, *'.B. /his is coere! on

the outer surface ith 3 c "a#er of insu"atin$ ateria"

hain$ > ; 0.0A *'.B. /he innerost surface is at 1000oC

an! the outerost surface is at ,0oC. Ca"cu"ate the stea!#

state heat transfer (er area.

=a("e 1

/inK /out. T='>4insu"ationT='>4firec"a#

;

So"ution: *e start ith the euation

=a("e 1 continue!


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Prof. R. Shanthi 56

=a("e 1 continue!

1000K ,04 .

0.03'0.0A40.21'1.0,4;

; 1522.6 *'2.

=a("e 2


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Prof. R. Shanthi 5A

*e ant to re!uce the heat "oss in =a("e 1 to 960 *'2.

*hat shou"! )e the insu"ation thic>ness+

=a("e 2

/inK /out

.

T='>4insu"ationT='>4firec"a#;


1000K ,04

T=4insu"ation'0.0A40.21'1.0,4;

.

; 960 *'2

T=4insu"ation ; 5.6 c

Con!uction throu$h ho""o c#"in!er


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Prof. R. Shanthi 5L

;

ri

ro

/i

/o

Con!uction throu$h the co(osite


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Prof. R. Shanthi 59

Con!uction throu$h the co(osite

a"" in a ho""o-c#"in!er

/iK /o.

I"nr2'r14J ' 2U>L;

r1

r2

/i

/o

r3

Materia"

I"nr3'r24J ' 2U>8L

Materia" 8

=a("e 3


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Prof. R. Shanthi 60

thic> a""e! tu)e of stain"ess stee" > ; 19 *'.B4 ith

2-c inner !iaeter an! ,-c outer !iaeter is coere!ith a 3-c "a#er of as)estos insu"ation > ; 0.2 *'.B4.

f the insi!e-a"" te(erature of the (i(e is aintaine! at

600oC an! the outsi!e of the insu"ation at 100oC ca"cu"ate

the heat "oss (er eter of "en$th.

=a("e 3

/iK /o.

I"nr2'r14J ' 2U>L;

I"nr3'r24J ' 2U>8L


=a("e 3 continue!


61/88

Prof. R. Shanthi 61

=a("e 3 continue!

2 U L 600 K 1004

.

I"n2'14J ' 19; I"n5'24J ' 0.2

.

L ; 6


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Prof. R. Shanthi 62


onductionis the flow of heat by direct contact between a warmer and a

cooler body.

on#ection

is the flow of heat carried by mo#ing gas or li!uid.$warm air rises, gi#es up heat, cools, then falls&

Gadiationis the flow of heat without need of an inter#ening medium.

$by infrared radiation, or light&

on#ection


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Prof. R. Shanthi 63

on#ectionConvectionis the (rocess in hich heatis carrie! fro

("ace to ("ace )# the )u"> oeent of a fluid $as or

"iui!4.

Conection currents are set u( hen

a (an of ater is heate!.

on#ection


64/88

Prof. R. Shanthi 6,

t e=("ains h# )reeEes coe fro the ocean in the !a#

an! fro the "an! at ni$ht

on#ection

on#ection" B t L @ f li


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Prof. R. Shanthi 65

on#ection" BewtonLs @aw of ooling

.

con. ; h /surfaceK /f"ui!4

rea e=(ose!

Heat transfer coefficientin *'2.B4

Heate! surface at /surface

"oin$ f"ui! at /f"ui!

on#ection" B t L @ f li


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Prof. R. Shanthi 66

.

con.

/surfaceK /f"ui!

Heate! surface at /surface

"oin$ f"ui! at /f"ui!

; 1'h4

Convective heat resistancein B'*4

on#ection" BewtonLs @aw of ooling

=a("e ,


67/88

Prof. R. Shanthi 6A

/he conection heat transfer coefficient )eteen a surface at 50oC an!

a)ient air at 30oC is 20 *'2.B. Ca"cu"ate the heat f"u= "eain$ the

surface )# conection.

=a("e ,

So"ution:

Heate! surface at /surface ; 50oC

"oin$ f"ui! at /f"ui! ; 30oC

h ; 20 *'2.B

.

con.; h /surfaceK /f"ui!4

; 20 *'2.B4 = = 50-304oC

. con.

; 20 = 20 ; ,00 *'2

Heat f"u= "eain$ the surface:

se 7etons La of coo"in$ :

=a("e 5


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Prof. R. Shanthi 64

C#erall Heat Transfer through a Mlane Wall


73/88

Prof. R. Shanthi A3

g

. /

K /1;

1'h4

/2

K /8;

1'h84

/1

K /2;

T='>4

. /K /8

;1'h4 1'h84 T='>4

/K /84;

1' ; 1'h 1'h8 T='>

here is the oera"" heat transfer coefficient $ien )#

.

Dera"" heat transfer throu$h ho""o-c#"in!er


74/88

Prof. R. Shanthi A,

$ #

ri

ro/i

/o

L

/K /84;

1' ; 1'hi4 1'h8o4

.

"ui! is insi!e the (i(e

"ui! 8 is outsi!e the (i(e

/X /8

"nro'ri4 ' 2U>L

here

=a("e 6


75/88

Prof. R. Shanthi A5

Stea at 120oC f"os in an insu"ate! (i(e. /he (i(e is

i"! stee" > ; ,5 *' B4 an! has an insi!e ra!ius of 5c an! an outsi!e ra!ius of 5.5 c. /he (i(e is coere!

ith a 2.5 c "a#er of ; 0.0A *' B4.

/he insi!e heat transfer coefficient hi4 is


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Prof. R. Shanthi A6

=a("e 6 continue!

1' ; 1'


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Prof. R. Shanthi AA

=a("e 6 continue!

.

120 K 354;

;


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Prof. R. Shanthi A

Documents

PM3125 Lectures 6to9 Heat Transfer