Analytic Combustion: With Thermodynamics, Chemical Kinetics and Mass Transfer

413 Pages·2020·6.184 MB·English

by  Anil Waman Date

Anil Waman Date
Analytic
Combustion
With Thermodynamics, Chemical
Kinetics and Mass Transfer
Second Edition
Analytic Combustion
Anil Waman Date
Analytic Combustion
With Thermodynamics, Chemical Kinetics
and Mass Transfer
Second Edition
123
Anil WamanDate
Department ofMechanical Engineering
Indian Institute of Technology Bombay
Mumbai,Maharashtra, India
ISBN978-981-15-1852-2 ISBN978-981-15-1853-9 (eBook)
https://doi.org/10.1007/978-981-15-1853-9
©SpringerNatureSingaporePteLtd.2020
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Preface to Second Edition
Itisalmost9yearssincethefirsteditionofAnalyticCombustionwaspublishedby
the Cambridge University Press, New York. However, my postretirement reap-
pointmentin2017asAdjunctProfessorbytheDirector,IITBombay(Prof.Devang
Khakhar) gave me the opportunity to undertake a fresh review of the book. The
review revealed typographic errors in my LaTex files as well as printer’s devils in
the published copies of the book.
In this revised edition, while the overall structure and the emphasis of the book
havebeenretained,insomechaptersnewsectionsareaddedorthetextmaterialhas
been better cross-referenced. At this point, I must draw special attention of the
reader to the two case studies presented in Chap. 11. They pertain to modeling of
(i) an experimental wood-burning cookstove from CTARA1 and (ii) UNDP
approved design of the Vertical Shaft Brick Kiln (VSBK) originally from rural
China. Both are complex systems that require recall offundamentals as well as of
practical field observations in rural settings to guide modeling considerations.
I emphasize this because increasingly, the world over, researchers are seeking to
apply formal tools of combustion science to retrofit or to redesign such rural
technologies for meeting goals of sustainable development.
In this post-retirement period, I often had to call upon my faculty aswell as
non-faculty colleagues and students from Mechanical Engineering Department
andfromCTARAtohelpmeinmanyindirectwaystopreparetherevisedmanuscript.
Itistotheircreditthattheyungrudginglyofferedthishelpasandwhenrequired.
1CentreforTechnologyAlternativesforRuralareas,IITBombay.
v
vi PrefacetoSecondEdition
Finally, I would like to express my special gratitude to Ms. Swati Meherishi,
SeniorEditor-AppliedScienceandEngineering,Springerforherconsiderableadvice
andguidanceduringthepreparationofthemanuscriptforthissecondedition.Iwould
alsoliketothankMr.LokeshwaranandMr.ManiarasanGandhiforengagingwith
methroughseveralemailstotakethebookthroughitsproductionstages.
April–June 2019 Anil Waman Date
IIT Bombay, Bombay, India
Preface to First Edition
Itisfairtosaythataverysubstantialpart(over90percent)ofthetotalenergyused
today in transportation, power production, space heating, and domestic cooking is
producedbycombustion(burning)ofsolid,liquid,andgaseousfuels.Althoughthe
phenomenonofcombustionhasbeenknowntotheearliestman,andalthoughgreat
strideshavebeenmadethroughpainstakingexperimentalandtheoreticalresearchto
understand this phenomenon and to use this understanding in designs of practical
equipment(principally,burnersandcombustionschambersorfurnaces),anyclaim
to a perfect science of combustion remains as illusive as ever. Designers of com-
bustionequipmentthusrelygreatlyonexperimentaldataandempiricalcorrelations.
Combustionisaphenomenonthatinvolvesthechangeinthechemicalstateofa
substancefrom afuelstatetoaproductstateviaachemicalreactionaccompanied
by the release of heat energy. To the extent that a change of state is involved, the
lawsofThermodynamicsprovidethebackbonetothestudyofcombustion.Design
of practical combustion equipment, however, requires further information in the
form of the rate of change of state. This information is provided by the empirical
sciences of Heat and Mass Transfer coupled with Chemical Kinetics. In addition,
the rate of change is also governed by Fluid Mechanics.
Theheatreleasedbycombustionisprincipallyusedtoproducemechanicalwork
in engines and power plants, or is used directly in applications such as
space-heatingorcooking.Combustioncanalsoproduceadverseimpacts,however,
as in a fire or in causing pollution from the products of combustion. Thus,
understandingofcombustionisnecessaryforproducingusefuleffectsaswellasfor
fireextinctionandpollutionabatement.Inearliertimes,pollutionwasregardedasa
very local phenomenon (comprising smoke and particulates, for example).
However, recognition of the so-called greenhouse gases (which are essentially
productsofcombustion) andtheireffectonglobalclimate change hasgiven added
impetus to the study of combustion.
Theforegoingwillinformthereader thatthescope for thestudyofcombustion
is, indeed, very vast. A book that is primarily written for postgraduate students of
mechanical, aeronautical, and chemical engineering must, therefore, inevitably
make compromises in coverage and emphasis. Available books on combustion,
vii
viii PrefacetoFirstEdition
though reflecting these compromises, cannot be said to have arrived at an agree-
ment on a standard set of topics or on the manner of their presentation. Much
depends on the background and familiarity of the authors with this vast and
intriguing subject. Deciding on coverage for postgraduate teaching is also further
complicatedbythefactthatinatypicalundergraduateprogram,studentsoftenhave
inadequate, or no, exposure to three subjects; namely, mass transfer, chemical
kinetics, and thermodynamics of mixtures.
ItiswithgratitudethatIacknowledgethatthisbookdrawsextensivelyfromthe
writingsofProfessorD.B.Spalding(FRS,formerlyatImperialCollegeofScience
andTechnology,London)onthesubjectsofcombustion,heat,andmasstransfer.In
particular, I have drawn inspiration from Spalding’s Combustion and Mass
Transfer.Thebook,inmyreckoning,providesanappropriatemixoftheessentials
of the theory of combustion and their use in understanding the principles guiding
the design of practical equipment involving combustion.
Thetopicsinthisbookhavebeenarrivedatiterativelyfollowingtheexperience
of teaching an Advanced Thermodynamics and Combustion course to dual-degree
(BTech + MTech) and MTech students in the Thermal and Fluids Engineering
stream in the Mechanical Engineering Department of IIT Bombay. The book is
divided into 11 chapters.
Chapter1establishesthelinksbetweencombustionanditsfourneighborsmen-
tioned above. Chapter 2 deals with the thermodynamics of a pure substance; thus
servingtorefreshmaterialfamiliartoanundergraduatestudent.Chapter3dealswith
thethermodynamicsofinert(non-reacting)andreactinggaseousmixtures.Learning
toevaluatepropertiesofmixturesfromthoseofindividualspeciesthatcomprisethem
isanimportantpreliminary.InChapter3,thisaspecthasbeenemphasized.
StoichiometryandChemicalEquilibriumareidealizationsthatareimportantfor
defining the product states resulting from a chemical reaction. The product states
are evaluated by invoking implications of the law of conservation of mass and the
Second law of thermodynamics. These topics are discussed in Chapter 4.
Productstatesresultingfromrealcombustionreactionsinrealequipmentdonot,
in general, conform to those discussed in Chapter 4. This is because the real
reactions proceed at finite rate. As mentioned previously, this rate is governed by
chemical kinetics, diffusion/convection mass transfer, and fluid mechanics (turbu-
lence,inparticular).Chapter5makesthefirstforayintotheworldofrealchemical
reactions by introducing chemical kinetics. Construction of a global reaction from
postulatedelementalreactionsisdiscussedinthischapter;besideslistingtheglobal
rate constants for hydrocarbon fuels.
Inpracticalequipment,thestatesofareactingmixturearestronglyinfluencedby
the transport processes of heat, mass, and momentum in flowing mixtures. These
transport processes, in turn, are governed by fundamental equations of mass,
momentum (the Navier–Stokes equations), and energy transfer. Therefore, these
three-dimensional equations are derived in Chapter 6 along with simplifications
(such as the boundary layer flow model, Stefan tube model, and Reynolds flow
model) that are commonly used in a preliminary analysis of combustion
PrefacetoFirstEdition ix
phenomena. It is important to recognize that chemical kinetics, heat, and mass
transfer, and fluid mechanics are rigorous independent subjects in their own right.
ThematerialinChapters4,5,and6,inprinciple,canbeappliedtotheanalysisof
combustion in practical equipment. However, to yield useful quantitative informa-
tion, the use of computers with elaborate programs becomes necessary. An intro-
ductory analysis can nonetheless be performed by making idealizations and
introducingassumptions.Incombustionengineering,theseidealizationsofpractical
equipment are called Thermo-Chemical Reactors. Chapter 7 thus presents the
analysis of three types of reactors, namely: Plug-flow reactor, Well-stirred reactor,
andConstant-massreactor.Mathematicalmodelsofsuchreactorscanbeappliedto
severalcombustiondevicessuchasgas-turbinecombustionchambers,fluidized-bed
combustion, fixed bed combustion, biomass gasifiers, and combustion in internal
combustion engines.
When fuels burn, they do so with a visible-to-the-eye zone called a flame.
Acloserexaminationofcombustioninpracticalequipment,ofcourse,requiresthe
studyofpropertiesofflames.Chapter8thusdealswithpremixedflamesbecausein
many combustion devices, gaseous fuel is premixed with air before entering the
combustion space through a burner. Phenomena such as flame ignition, propaga-
tion, stabilization, and quenching can be studied by applying simplified equations
governing premixed flames.
Gaseousfuelsarealsoburnedwithoutpremixingwithair.Inthesesituations,the
air required for combustion is drawn from surroundings by processes of diffusion
and entrainment. Flames formed in this manner are called diffusion flames.
Mathematical treatment of such flames requires the solution of multidimensional
equations. Diffusion flames are discussed in Chapter 9.
Burning of solid particles (pulverized coal combustion, for example) or liquid
droplets(or,sprays)canbeviewedasinter-phasemasstransferphenomenabecause
the change in state is accompanied by a change in phase; from solid (or liquid) to
gaseousphase.Typically,insolidscombustion,thisphasechangeisaccompaniedby
heterogeneouscombustionreactionsattheinterface.Theproductsofthesereactions
(alongwithvolatiles)thenburninthegaseousphasethroughhomogeneousreactions.
Involatileliquidfuelburning,thereisnoheterogeneousreactionbutphasechange
takesplace(withoutachangeinthechemicalcompositionofthefuel)owingtolatent
heattransferfromthegaseousphase.Treatmentofboththesetypesofphenomenacan
be generalized through simplified models introduced in Chapter 6. Chapter 10 is
devotedtotheestimationofburningratesofsolidandliquidfuels.
Finally,inChapter11,examplesofpredictionofcombustioninpracticaldevices
are presented. The purpose of this chapter is to introduce the reader to the type of
predictions obtained by integrating various modeling techniques.
x PrefacetoFirstEdition
In each chapter, several solved problems are presented. In addition, there are
severalexerciseproblemsattheendofeachchapter.Althoughsomeproblemscan
besolvedusingapocketcalculator,otherswillrequirewritingcomputercodes.The
reader is strongly advised to solve these problems to assimilate the text material.
June 2010 Anil Waman Date
IIT Bombay, Bombay, India