Fundamentals Exam Review - Thermodynamics

7/18/2019 Fundamentals Exam Review - Thermodynamics

http://slidepdf.com/reader/full/fundamentals-exam-review-thermodynamics 1/84

+FEFE

ThermodynamicThermodynamicss

ReviewReview

Dr. Omar MezaDr. Omar Meza

Assistant ProfessorAssistant Professor

Department of MechanicalDepartment of MechanicalEngineeringEngineering



+Topics coveredTopics covered

Thermodynamics LawThermodynamics Law 11stst and 2and 2ndnd lawlaw

Energy , heat and workEnergy , heat and work

Availability and reversibilityAvailability and reversibility CyclesCycles

Ideal gasesIdeal gases

i!t"re o# gasesi!t"re o# gases

$hase change$hase change %eat Trans#er %eat Trans#er

$roperties o#&$roperties o#& enthalpyenthalpy entropyentropy



+Tips #or taking e!amTips #or taking e!am

'se the re#erence handbook'se the re#erence handbook (now what it contains(now what it contains (now what types o# problems yo" can "se it #or (now what types o# problems yo" can "se it #or (now how to "se it to solve problems(now how to "se it to solve problems

)e#er to it #re*"ently)e#er to it #re*"ently ork backwards when possibleork backwards when possible

E e!am is m"ltiple choice with single correct answer E e!am is m"ltiple choice with single correct answer $l"g answers into problem when it is convenient to do so$l"g answers into problem when it is convenient to do so Try to work backwards to con#irm yo"r sol"tion as o#ten asTry to work backwards to con#irm yo"r sol"tion as o#ten as

possiblepossible $rogress #rom easiest to hardest problem$rogress #rom easiest to hardest problem

-ame n"mber o# points per problem-ame n"mber o# points per problem Calc"lator tipsCalc"lator tips

Check the .CEE- website to con#irm yo"r model is allowedCheck the .CEE- website to con#irm yo"r model is allowed Avoid "sing it to save time/Avoid "sing it to save time/ any answers do not re*"ire a calc"lator 0#ractions vs decimalsany answers do not re*"ire a calc"lator 0#ractions vs decimals



+$roperties o# -ingle3Component$roperties o# -ingle3Component

-ystems-ystems

%andbook page&%andbook page&

or a simple s"bstance,or a simple s"bstance,

speci#ication o# anyspeci#ication o# any twotwointensive, independentintensive, independent

propertiesproperties is s"##icient tois s"##icient to

#i! all the rest#i! all the rest




-ystems-ystems


A s"bstance that has aA s"bstance that has a

#i!ed chemical#i!ed chemicalcomposition thro"gho"tcomposition thro"gho"t

is called ais called a p"re s"bstancep"re s"bstance




-ystems-ystemsA s"bstance whose properties are "ni#orm thro"gho"t isA s"bstance whose properties are "ni#orm thro"gho"t is

re#erred to asre#erred to as

AAA solidA solid

44An ideal s"bstanceAn ideal s"bstanceCCA p"re s"bstanceA p"re s"bstance

55A standard s"bstanceA standard s"bstance

A s"bstance whose properties are "ni#orm thro"gho"t isA s"bstance whose properties are "ni#orm thro"gho"t is

re#erred to asre#erred to asAAA solidA solid

44An ideal s"bstanceAn ideal s"bstance

CCA p"re s"bstanceA p"re s"bstance

55A standard s"bstanceA standard s"bstance




-ystems-ystems




-ystems-ystems 6iven&6iven& -team at 27 k$a is sat"rated at 189-team at 27 k$a is sat"rated at 189 ooC In whatC In what

state will the steam be at :7state will the steam be at :7 ooC i# the press"re is 27 k$a;C i# the press"re is 27 k$a;

Analysis&Analysis&

< $ = 27 k$a, T< $ = 27 k$a, Tsatsat = 189= 189ooCC

TTsatsat > T> T ?s"perheated vapor@?s"perheated vapor@

Tsat= 189Tsat= 189ooCC

T= :7T= :7ooCC




-ystems-ystems




-ystems-ystems ind the vol"me occ"pied by 27 kg o# steam at 7: $a,ind the vol"me occ"pied by 27 kg o# steam at 7: $a,

:77:77ooCC

At 7: $a the TAt 7: $a the Tsatsat=1:2=1:2ooC appro!imately It means that theC appro!imately It means that the

steam is in thesteam is in the s"perheated regions"perheated region




-ystems-ystems


)eal gases e!hibit ideal3)eal gases e!hibit ideal3

gas behavior at relativelygas behavior at relativelylow press"res and highlow press"res and high

temperat"restemperat"res




-ystems-ystemsAll real gases deviate somewhat #rom ideal gas behavior& $=All real gases deviate somewhat #rom ideal gas behavior& $=

m)T or which o# the #ollowing conditions is the deviationm)T or which o# the #ollowing conditions is the deviation

the smallest;the smallest;

AA

%igh temperat"re and low vol"me%igh temperat"re and low vol"me44%igh temperat"re and low press"res%igh temperat"re and low press"res

CC%igh press"res and low vol"mes%igh press"res and low vol"mes

55%igh press"re and low temperat"res%igh press"re and low temperat"res

hen the vol"me o# an ideal gas is do"bled while thehen the vol"me o# an ideal gas is do"bled while the

temperat"re is halved, what happens to the press"re;temperat"re is halved, what happens to the press"re;AA$ress"re is do"bled$ress"re is do"bled

44$ress"re is halved$ress"re is halved

CC$ress"re is *"artered$ress"re is *"artered

55$ress"re is *"adr"pled$ress"re is *"adr"pled

4

P

=X

T

Xv4=

)2/ T(

)v2(X=

T

Pv




-ystems-ystems





-ystems-ystems




-ystems-ystems



+irst Law o# Thermodynamicsirst Law o# Thermodynamics






( ) ( ) PEΔ+KEΔ+UΔ=Wout-Win+Qout-Qin

ormal sign convention: Heat transfer to asystem and work done by a system are

positive; heat transfer from a system and workdone on a system are negative.

W b is positive for expansion

W b is negative for compression







5"ring a process, B7 o# work are done by a closed5"ring a process, B7 o# work are done by a closed

stationary system on its s"rro"ndings The internal energystationary system on its s"rro"ndings The internal energy

o# the system decreases by :7 D hat is the heat trans#er;o# the system decreases by :7 D hat is the heat trans#er;

( ) ( ) PE KE U ∆+∆+∆=Wout-Win+Qout-Qin

U ∆=Wout-Qnet

WoutQnet +∆= U

J J J 103040Qnet −=+−=








Calc"late the work done by a piston contained within aCalc"late the work done by a piston contained within a

cylinder with air i# 2mcylinder with air i# 2mBB is tripled while the temperat"re isis tripled while the temperat"re is

maintained at a constant T = B7maintained at a constant T = B7ooC The initial press"re isC The initial press"re is

$$11=:77 k$a absol"te=:77 k$a absol"te




Polytropic process in a closed system






























A steam coil operating at steady state receives B7 kgmin o#A steam coil operating at steady state receives B7 kgmin o#

steam with an enthalpy o# 2F77 kkg i# the steam leavessteam with an enthalpy o# 2F77 kkg i# the steam leaves

with an enthalpy o# 1G77 kmin, what is the rate o# heatwith an enthalpy o# 1G77 kmin, what is the rate o# heat

trans#er #rom the coil;trans#er #rom the coil;









+4asic Cycles4asic Cycles


















































+




+






+




+



+Ideal 6as i!t"reIdeal 6as i!t"re


+






+




+



+$sychrometrics$sychrometrics


+





ollier 5iagramollier 5iagram

+




+




+




+




+




+




+




+




+




+



+Comb"stion $rocessesComb"stion $rocesses

+




+




+




+




+



+-econd Law o# Thermodynamics-econd Law o# Thermodynamics


+




Part of the heat received by a heat

engine is converted to work, while the

rest is rejected to a sink.

This is a law.1.It is always observed in real heat engines.

.!ne cannot derive it from first principles.

".#o exceptions are known.

It is not j$st that we haven%t looked hard

eno$gh and that f$t$re discoveries will makeit possible to convert heat completely to work.

+




+



-econd Law o# Thermodynamics-econd Law o# Thermodynamics

The efficiency of a refrigerator isexpressed in terms of the

coe##icient o# per#ormance &'!P(.

The objective of a refrigerator is to

remove heat &QL( from the

refrigerated space.

'an the val$e of '!P)

be greater than $nity*

+




The work

s$pplied to a

heat p$mp is

$sed to

extract energy

from the cold

o$tdoors and

carry it into

the warm

indoors.

for fixed val$es of QL and QH

+- d # Th d i




+( 1--/0

( 2--/0

'( 3--/0

4( 1--/0

+- d L # Th d i




+( 5es( #o

'( #ot clear

4( #+

+E t



EntropyEntropy

+E tE t



EntropyEntropy

+( .6 k789( 2.62 k789

'( 6.1- k789

4( 6.1- k789

+



Pregntas!Pregntas!"omentarios!"omentarios!

+



MchasMchas

#racias $#racias $

Documents

Fundamentals Exam Review - Thermodynamics