thermo chapter 3.pptx
-
Upload
mohd-azizi -
Category
Documents
-
view
224 -
download
0
Transcript of thermo chapter 3.pptx
-
8/17/2019 thermo chapter 3.pptx
1/27
Chapter 3:ENERGY, ENERGY
TRANSFER AND GENERALENERGY ANALYSIS
CHE 433 THERMODYNAMICS
-
8/17/2019 thermo chapter 3.pptx
2/27
FORMS OF ENERGY
Energy can exist in numerous forms suc as terma!"mecanica!" #inetic" $otentia!" e!ectric" magnetic" cemica!"an% nuc!ear" an% teir sum constitutes te total energy, E of a system&
Termo%ynamics %ea!s on!y 'it te change of te tota!energy&
Macrocop!c forms of energy( Tose re!ate% to motion an%te in)uence of some externa! e*ects suc as gra+ity"magnetism" e!ectricity an% surface tension& E&g& #inetic an%$otentia! energies&
M!crocop!c forms of energy( Tose re!ate% to te
mo!ecu!ar structure of a system an% te %egree of temo!ecu!ar acti+ity& Internal energy, U( Te sum of a!! te microsco$ic forms
of energy&
, Te macrosco$ic energy of ano-.ect canges 'it +e!ocity an%
-
8/17/2019 thermo chapter 3.pptx
3/27
"!net!c energy, "E( Te energy tat a system$ossesses as a resu!t of its motion re!ati+e tosome reference frame&
#otent!al energy, #E: Te energy tat a system$ossesses as a resu!t of its e!e+ation in agra+itationa! /e!%&
3
0inetic energy $er unitmass
0inetic energy
1otentia! energy $er unitmass
1otentia!energy
-
8/17/2019 thermo chapter 3.pptx
4/27
4
Tota! energyof a system
Energy of a
system $er unitmass
Tota! energy$er unit mass
Mass )o'rate
Energy )o' rate
Cloe$ yte% remain stationary%uring a $rocess an% tus no cangein 1E an% 0E 2tat!onary yte%&
∆E ∆5Control &ol'%e in+o!+e )ui% )o' for!ong $erio%s of time& It is con+enientto ex$ress te energy )o' in te rate
form -y incor$orating te mass )o'rate (the amount of mass owing
agnetic" e!ectric an% surface tension e*ects are usua!!y ignore%&
-
8/17/2019 thermo chapter 3.pptx
5/27
ENERGY TRANSFER (Y )EAT
6
Energy can cross te-oun%aries of a c!ose%system in te form ofheat an% *or+ &
Tem$erature %i*erence is te%ri+ing force for eat transfer& Te!arger te tem$erature %i*erence"te iger is te rate of eattransfer&
)eat( Energy tat istransferre% -et'een t'o
systems 2or a system an% itssurroun%ings -ecause of a
-
8/17/2019 thermo chapter 3.pptx
6/27
7
During an a%ia-atic $rocess" asystem excanges no eat 'it itssurroun%ings&
Amount of eat transfer'en eat transfer ratecanges 'it time
Amount of eat transfer'en eat transfer rate is
constant
Heat transfer $er unitmass
Tere are t'o 'ays a $rocess can -ea%ia-atic(8 Te system is 'e!! insu!ate% so taton!y a neg!igi-!e amount of eat can
$ass troug te -oun%ary8 9ot system an% surroun%ings are atte same tem$erature 2no %ri+ing forcefor eat transfer&
-
8/17/2019 thermo chapter 3.pptx
7/27
ENERGY TRANSFER (Y OR"
or+ ( Te energy transfer associate% 'it a force acting troug a%istance& A r!!ng p!ton, a rotat!ng ha-t, an% an electr!c *!re
cro!ng the yte% .o'n$ar!e are a!! associate% 'it 'or#interactions
For%al !gn con&ent!on( Heat transfer to a system and work doneby a system are positive; heat transfer from a system and work doneon a system are negative&
A!ternati+e to sign con+ention is to use te su-scri$ts in an% out toin%icate %irection&
:S$ecifying te%irections of eat an%
;or# %one$er unitmass
1o'er is te'or# %one$er unit time
-
8/17/2019 thermo chapter 3.pptx
8/27<
)eat &/ or+ 9ot are recogni=e% at te
-oun%aries of a system as teycross te -oun%aries& Tat is" -ot
eat an% 'or# are boundary$enomena& Systems $ossess energy" -ut not
eat or 'or#& 9ot are associate% 'it a
process, not a state& 5n!i#e$ro$erties" eat or 'or# as no
meaning at a state& 9ot are path functions 2i&e&" teir
magnitu%es %e$en% on te $atfo!!o'e% %uring a $rocess as 'e!!as te en% states&
1ro$erties are $oint functions>-ut eat an% 'or# are $atfunctions 2teir magnitu%es%e$en% on te $at fo!!o'e%&
1ro$erties are $oint functions a+eexact %i*erentia!s 2d &
1at functions a+e inexact%i*erentia!s 2δ
-
8/17/2019 thermo chapter 3.pptx
9/27
MEC)ANICAL FORMS OF OR"
Tere are t'o re?uirements for a 'or# interaction-et'een a system an% its surroun%ings to exist( tere must -e a force acting on te -oun%ary& te -oun%ary must move.
@ Te 'or# %one is $ro$ortiona! to teforce a$$!ie% 2F an% te %istance
;or# orce × Distance
;en force is notconstant
If tere is nomo+ement" no 'or# is%one&
-
8/17/2019 thermo chapter 3.pptx
10/27B
Sha-tor+
Energy transmission troug rotating
safts is common!y encountere% in$ractice&
Saft 'or# is $ro$ortiona! tote tor?ue a$$!ie% an% tenum-er of re+o!utions of te
A force F actingtroug a momentarm r generates a
tor?ue T Tis force acts troug a %istance
s
Te $o'er transmitte% troug te
saft is te saft 'or# %one $erunit time
Saft'or#
-
8/17/2019 thermo chapter 3.pptx
11/27
E0a%ple 1
Determine te $o'er transmitte% troug tesaft of a car 'en te tor?ue a$$!ie% is , N&man% te saft rotates at a rate of 4
re+o!utions $er minute 2r$m&
BB
( ) ( )4000 1min 1
2 2 200min 60 1000
83.8
sh
kJ W nT N m
s N m
kW
π π = = × ÷ ÷ ÷×
=
-
8/17/2019 thermo chapter 3.pptx
12/27B,
pr ngor+
E!ongationof a s$ringun%er tein)uence
of a force&
;en a force is a$$!ie% on a s$ring"te !engt of te s$ring canges&
or !inear e!astic s$rings" te%is$!acement x is $ro$ortiona! to te
force a$$!ie% k s$ring constant2#Nm
Su-stituting an% integratingyie!%
x B an% x ,( te initia! an% te
/na! %is$!acements
Te %is$!acement of a!inear s$ring %ou-!es'en te force is
;en te !engt of te s$ringcanges -y
a %i*erentia! amount dx un%er tein)uence of a force F " te 'or# %oneis
-
8/17/2019 thermo chapter 3.pptx
13/27
E0a%ple 2
Determine 'or# re?uire% 2in #F to com$ress as$ring 'ose s$ring constant is 3 #Nm a%istance of 3 cm from its un!oa%e% !engt&
B3
( )
( )
2 2 2 2 2
2 1
1 1 1
2 2
2 2
3000.03 0
20.135
10.135 0.135
1
x xW Fds kxdx k xdx k
kN mm
kN m
kJ kN m kJ
kN m
= = = = − ÷
= − = ×
= × = ÷×
∫ ∫ ∫
+ D
-
8/17/2019 thermo chapter 3.pptx
14/27B4
or+ Done onElat!c Sol!$(ar
So!i% -ars-ea+e ass$ringsun%er tein)uence of
a force& Stretcing a !i?ui% /!m 'it amo+a-!e 'ire&
A cross sectiona! areaσ norma! stress 2as $ressureunits
orAoc!ate$ *!ththe Stretch!ng
o- a L!'!$ F!l%
2
2
surface tension force per unit length
s
s
dA b dx
F bσ
σ
==
=
+ D t R ! t
-
8/17/2019 thermo chapter 3.pptx
15/27B6
or+ Done to Ra!e or toAccelerate a (o$yB& Te 'or# transfer nee%e%
to raise a -o%y is e?ua! tote cange in te$otentia! energy of te-o%y&
,& Te 'or# transfer nee%e%
to acce!erate a -o%y ise?ua! to te cange in te#inetic energy of te -o%y&
Te energy
transferre% to a-o%y 'i!e -eingraise% is e?ua! tote cange in its$otentia! energy&
-
8/17/2019 thermo chapter 3.pptx
16/27
E0a%ple 3
Determine te energy re?uire% to acce!erate an
-
8/17/2019 thermo chapter 3.pptx
17/27
E0a%ple 4
A %amage% B, #g car is -eing to'e% -y atruc#& Neg!ecting te friction" air %rag" an% ro!!ingresistance" %etermine te extra $o'er re?uire%
2a for constant +e!ocity on a !e+e! roa%2- for constant +e!ocity of 6 #m on a 3o 2from ori=onta! u$i!! roa%2c to acce!erate on a !e+e! roa% from sto$ to @#m in B, s&
B:
-
8/17/2019 thermo chapter 3.pptx
18/27
B<
( )
( ) ( )
2 1
2
2 2
Power require is the sum of the rates of changes in potential an !inetic energies
" #
" # 0
sin30
50000 11200 9.81
3600 1000
total a g
a
o
total g
W W W
a zero
b W z
W W mg z z t mg mgV t
m kJ kg kg m s
s m s
= +
=∆
= = − ∆ = =∆
= ÷
( )
( ) ( ) ( )2
2 2
2 1 2 2
0.5 81.$
" # 0
1 1 90000 11200 0 12 31.3
2 2 3600 1000
g
total a
kW
c W
m kJ kg W W m V V t kg s kW
s m s
=÷
= = = − ∆ = − = ÷ ÷ ÷ ÷
-
8/17/2019 thermo chapter 3.pptx
19/27
Non5%echan!cal For%o- or+
Electr!cal *or+ ( Te genera!i=e% force is tevo!tage 2te e!ectrica! $otentia! an% tegenera!i=e% %is$!acement is te e!ectrica! charge.
Magnet!c *or+ ( Te genera!i=e% force is temagnetic "e!d strength an% te genera!i=e%%is$!acement is te tota! magnetic dipo!emoment .
Electr!cal polar!6at!on *or+ ( Te genera!i=e%force is te e!ectric "e!d strength an% tegenera!i=e% %is$!acement is te po!ari#ation ofthe medium.
B@
-
8/17/2019 thermo chapter 3.pptx
20/27
,
Electr!cal or+
E!ectrica! $o'er in terms ofresistance $" current %" an%$otentia! %i*erence 7&
E!ectrica! 'or#
E!ectrica!
$o'er
;en $otentia! %i*erencean% current cange 'ittime
;en $otentia!%i*erence an% current
remain constant
N e!ectrica!carge )o'
-
8/17/2019 thermo chapter 3.pptx
21/27
T)E FIRST LA OFT)ERMODYNAMICS The rst law of thermodynamics 8the conservation of energy
principle9 $ro+i%es a -asic to stu%y te re!ationsi$s among +ariousforms of energy an% energy interactions&
Te /rst !a' states tat energy can be neither created nordestroyed during a process; it can only change forms.
The First Law or a!! a%ia-atic $rocesses -et'een t'o s$eci/e%
states of a c!ose% system" te net 'or# %one is te same regar%!essof te nature of te c!ose% system an% te %etai!s of te $rocess&
,B
Energycannot -ecreate% or%estroye%>it can on!ycangeforms&
Te increase in te energy of a$otato in an o+en is e?ua! to teamount of eat transferre% to it&
-
8/17/2019 thermo chapter 3.pptx
22/27
,,
In te a-sence of any'or# interactions" teenergy cange of asystem is e?ua! to tenet eat transfer&
Te 'or#2e!ectrica!%one on ana%ia-atic
system is e?ua!to te increasein te energyof te system&
Te 'or#2saft %oneon ana%ia-aticsystem ise?ua! to teincrease in teenergy of tesystem&
Te energy cange of asystem %uring a $rocess ise?ua! to te net 'or# an%eat transfer -et'een te
-
8/17/2019 thermo chapter 3.pptx
23/27
Energy (alance
&he net change (increase or decrease) in the tota! energy ofthe system during a process is e'ua! to the dierencebetween the tota! energy entering and the tota! energy!eaving the system during that process.
,3
-
8/17/2019 thermo chapter 3.pptx
24/27
Energy Change o- a Syte%,Eyte%
,4
Energy can exist in numerous
forms suc as interna!" #inetic"$otentia!" e!ectric" magnetican% te sum constitute tetota! energy of te system" E&In te a-sence of e!ectric an%
magnetic e*ects"
-
8/17/2019 thermo chapter 3.pptx
25/27
Mechan!% o- EnergyTran-er, E!n an$ Eo't
,6
Heat transfer"G
;or#transfer" ;
Mass )o'" m
or constant rates"
In te rate form"
Energy
-a!ance $erunit mass
-
8/17/2019 thermo chapter 3.pptx
26/27
,7
Te energy content of a
contro! +o!ume can -ecange% -y mass )o' as'e!! as eat an% 'or#interactions&
or a cyc!e * " tus + * &
A c!ose% system %oesnot in+o!+e any mass
)o'" on!y eat transferan% 'or#&
Energy -a!ance for a cyc!e 2c!ose%system
;net"out ;out 8 ;in Gnet"in Gin 8 Gout
-
8/17/2019 thermo chapter 3.pptx
27/27
1RE1ARED 9Y(NORASMAH MOHAMMED MANSHORAC5TY O CHEMICA ENJINEERINJ" 5iTM SHAH AAM&B@,37