Solving Problems in Thermal Engineering: A Toolbox for Engineers

213 Pages·2020·6.719 MB·English

by  Viktor Józsa, Róbert Kovács

Power Systems
Viktor Józsa
Róbert Kovács
Solving
Problems
in Thermal
Engineering
A Toolbox for Engineers
Power Systems
Electrical power has been the technological foundation of industrial societies for
many years. Although thesystems designed to provide and apply electrical energy
have reached a high degree of maturity, unforeseen problems are constantly
encountered, necessitating the design of more efficient and reliable systems based
on novel technologies. The book series Power Systems is aimed at providing
detailed,accurateandsoundtechnicalinformationaboutthesenewdevelopmentsin
electrical power engineering. It includes topics on power generation, storage and
transmission as well as electrical machines. The monographs and advanced
textbooks in this series address researchers, lecturers, industrial engineers and
senior students in electrical engineering.
** Power Systems is indexed in Scopus**
More information about this series at http://www.springer.com/series/4622
ó ó á
Viktor J zsa R bert Kov cs
(cid:129)
Solving Problems in Thermal
Engineering
A Toolbox for Engineers
123
Viktor Józsa Róbert Kovács
Department ofEnergy Engineering Department ofEnergy Engineering
Faculty of MechanicalEngineering Faculty of MechanicalEngineering
BudapestUniversity of Technology BudapestUniversity of Technology
andEconomics andEconomics
Budapest, Hungary Budapest, Hungary
ISSN 1612-1287 ISSN 1860-4676 (electronic)
Power Systems
ISBN978-3-030-33474-1 ISBN978-3-030-33475-8 (eBook)
https://doi.org/10.1007/978-3-030-33475-8
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to the memory of our young colleague,
Gergely Novotni
and
to my wife, Ági, and our daughter, Julianna
Viktor Józsa
to my beloved parents
Róbert Kovács
Preface
Thermal analysis is often omitted in practical research and industrial applications
due to its secondary importance, hoping that heat will find its way in or out while
theequipmentisfullyfunctional.Themarketpulliscruel,therearestrictdeadlines
which usually does not allow a few extra days and engineer hours to spend.
Therefore,thermalengineersarerarelyemployedinsmallcompanieswhoactually
have serious thermal problems, leading to significant losses. In most cases, this
viewpoint is initially viable and safe. The reliable operation will be guaranteed if
enough tests were performed with the equipment. Nevertheless, malfunctions,
crashes, and other events are often originated from thermal problems, and they
comeupafterweeks,months,oryearsofuse.Theprincipalaimofthepresentbook
is providing practical tools for solving thermal problems at all levels from the
beginner to the researcher. It is always better to have a rough estimate in a paper
(yes, even today, papers help a lot in solving complex problems to have a good
overview from a distance of our eyes) than entirely omitting thermal evaluations
since one does not have the background or confidence in using the state-of-the-art
calculation tools.
Solving thermal problems require abstract thinking since a small temperature
difference does not hurt during testing, does not have color, odor, direction, and
others.Furthermore,thetimescaleofthermalproblemsisusuallyexceededthatof
chemical, fluid dynamical, and mechanical problems of the same physical size by
ordersofmagnitude.Therefore,oldchurchesandcastleswiththickwallsvarytheir
inside temperature marginally over the year while a tree trunk floating on a river
maytravelkilometersinanhour.Insteadofdiggingdeepintothemodernmethods
whichmightbeobsoleteinfewyearsoradecade,themainfocusofthisbookison
discussing the necessary viewpoint to solve thermal problems, emphasizing the
state-of-the-art challenges what should be solved for reliable operation or estima-
tion, and modernly, ensure smart energy use. This latter criterion became standard
since the beginning of the century; however, most of our current buildings,
machines were designed earlier when these requirements were secondary, calling
for a different design philosophy.
vii
viii Preface
Thisbookisdividedintosixchapterswhicharelooselyconnectedbutrepresent
different tools for solving thermal problems. Chapter 1 is focusing on the general
approach of thermal problems, which is recommended to start with for beginners
andindustrialengineers.Itdiscussesthefundamentalconceptsofathermalsystem,
including boundaries, and basic calculation methods for estimating the thermal
behavior.
Chapter 2 is the summary of the governing equations of heat conduction to
provide a framework of advanced modeling. It gives a brief overview of the
mathematical structure of particular models, including heat conduction, fluid
mechanics, diffusion and mechanics, situating them onto the same thermodynamic
ground. It mostly uses the approach of Classical Irreversible Thermodynamics but
also presents its possible extensions.
Chapter 3 is focusing on thermal problems in energy engineering through
several examples, concentrating on renewable technologies. To minimize our
ecologicalfootprint,weneedefficientmachinesforagiven purpose.However,the
losses are often realized as heat transfer or dissipation to the ambient. As our
presentmachineswhichweusetodaywilllikelyremaininservicefordecades,their
retrofit for efficient use of thermal energy is the problem of the present to solve.
Hence,besidessolarandwindapplications,combustionisalsodiscussedregardless
that is unpopular in the media.
The space industry has exploded since the introduction of private companies in
the past decade with viable plans to make commercial use of space resources.
Hence,Chap.4isdedicatedtodiscussingthethermalbalanceanditschallengesin
space. Nevertheless, most of the content can be directly applied to vacuum appli-
cations on Earth as well.
Chapter 5 focuses on the experimental proofs of non-Fourier thermal conduc-
tion.Thatis,itincludeslowandroomtemperaturemeasurementsinwhichvarious
phenomena are observed, such as second sound and ballistic propagation. It was
initially measured in cryogenic conditions, which is usually far from applications.
Nevertheless, the non-Fourier behavior was proven to be present even in room
temperature under unsteady conditions, requiring heterogeneous materials or
nano-sized objects. Typically, composites and layered structures from distinct
materials fall into this category. Since the appearance of the non-Fourier behavior
dependsontheparticularlengthandtimescales,oneshouldbeawareofthese,and
that advanced thermal conduction models exist which are likely to appear in
commercial simulation software codes in the near future.
NumericalmethodsarediscussedinChap.6,focusingontheimplementationof
boundary conditions both from numerical and analytical aspects. Furthermore, a
particular way of error estimation is demonstrated on a conservative system which
makes apparent how easy to obtain stable, but unphysical solutions. It affects all
software.Therelevanceofthischapteristhatsimulationmodulesareavailableina
rapidlyincreasingnumberofengineeringsoftware.Itisoftenafewclicksona3D
drawingtogetathermalanalysiswithaconvergentresult.However,theusermust
beawarethatthemodelalways remains anestimate oftherealprocess.Therefore,
careful validation and method analysis are required prior to making any decision
Preface ix
based on a colorful result to avoid spectacular mechanical, thermal, and financial
failures.
Theproblemswhichwefeelinourskinrangefromthesizeofourplanetdown
to the nano-size scale in the semiconductor industry where the continuum-based
physics is still applicable. Consequently, understanding the governing logic and
using the appropriate mathematical tools allow us to build a versatile knowledge
independent of the given application and available software in the market.
Wishing you joy and persistence in your life and career,
Budapest, Hungary Viktor Józsa
Róbert Kovács
Acknowledgements
TheauthorsthankTamásFülöp,PéterVán,MátáysSzücs,GregoryKowalski,and
the BME Combustion Research Group for their valuable ideas, and their support.
The work was supported by the grants National Research, Development and
InnovationOffice—NKFIH116197(116375),124366(124508),123815,KH130378,
FK124704, and FIEK-16-1-2016-0007, New National Excellence Program of the
Ministry of Human Capacities ÚNKP-19-4-BME-213, the János Bolyai Research
Scholarship of the Hungarian Academy of Sciences, and the NVIDIA Corporation
withthedonationoftheQuadroP6000whichwasusedforthecalculationspresented
inChap.4.TheresearchreportedinthispaperwassupportedbytheHigherEducation
Excellence Program of the Ministry of Human Capacities in the frame of
NanotechnologyresearchareaofBudapestUniversityofTechnologyandEconomics
(BMEFIKP-NANO).
We would like to thank the Elsevier, APS, and Taylor&Francis for the
permission to reuse the relevant figures.
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