Text: Y.A. Cengel, Introduction to thermodynamics andheat transfer, Irwin/McGraw-Hill, 1977
• This course follows ASEN 2002 and covers the SecondLaw of Thermodynamics, Entropy, Power/Energy Cyclesand Heat Transfer (conduction, convection and radiation).
• The emphasis will be on understanding the basic physicalprinciples associated with these topics and developing thestudent’s ability to solve numerical problems associated withthem.
• Experiments will be carried out to help the student gainexperience with the systems representing these principles.
Course Objectives
Given regular class attendance, reading of assigned textmaterial in preparation for quizzes, careful and comprehensivecompletion of all assignments, students should be able to:
(1) understand the general concepts of thermodynamics andheat transfer in order to develop an intuitive grasp of thesubject matter;
(2) develop an ability to apply these basic concepts toengineering design problems.
Course Structure
• The textbook will be followed closely but additional materialwill be introduced to broaden a particular subject.
• Students are expected to read the assigned textbook section intime to prepare for both in class discussion and for quizzesgiven approximately every other week.
• Homework assignments will be bi-weekly and will be due onTuesday of each following week.
• There will be 3 hour-long exams (the lowest score will bedropped in computing the final grade) and a final exam. All examswill be in-class and cover the material between it and the last exam.Exams may require tables and calculation so please bring yourbooks and calculators to class.
• All quizzes and exams will be open book and notes (but not openneighbor). Exams can be made up for valid and provenemergencies (illness, etc.).
• After the quizzes and exams are graded and returned we willgo over them to resolve any issues that were particularlyproblematical to the class.
• If you have any particular difficulty with a question or topicplease write it down and submit in written form (hardcopy oremail) so that we can go over it in class. You can also bring itup in class. In this way the whole class can benefit from thediscussion of problem topics.
• If you have complaints about the class please print it out andsubmit it anonymously by slipping it under my door when I amout (door is closed). I would prefer to improve the classexperience rather than finding out later when I can’t make anychanges.
Class Participation
• Class participation is strongly encouraged to both discuss thetext material and to respond to quiz and exam questions.Students are encouraged to ask constructive questions and tocontribute appropriate comments.
• We are all working together to learn this material and yourviewpoint of how you learned the material is very important tothe class. (I realize that this is NOT your favorite class so Ihope we can work together to make it more interesting for allof us.)
Grading
Hour Exams (3-1=2) 20%Final Exam 10%Quizzes 10%Homework 30%Experiments 30% (includes, test set-up,measurements, data reduction, report writing andpresentation)
* A large percentage is assigned to the homework and labwork.
Office Hours
• You are strongly encouraged to make good use of the officehours set aside for this class and of the TAs. These times areallocated for your benefit.
• If you are unable to come during office hours specialarrangements can be made by making an appointment with eitherinstructor or the TAs. It should be remembered that theseinstructors are busy with other classes and research projects.
• Please use email communications for both instructors and theTAs.
Other Course Policies
• It is the student’s responsibility to read assigned text chaptersto prepare for class discussions and unit quizzes. Students areexpected to do their own work during quizzes and exams andno communications between students will be allowed.
• We are all responsible for creating a respectful classroomwhere we can all learn the material at hand. If you do not wishto learn the material you are encouraged to drop the class earlyin the semester.
Syllabus for ASEN 3113: Thermodynamics of andHeat Transfer
I. Second Law of Thermodynamics (Chapter 5)
II. Entropy (Chapter 6), Phase and chemical equilibrium(handout), Psychrometrics (handout)
III. Power and refrigeration cycles (Chapter 7),
IV. Steady heat conduction (Chapter 8)
V. Transient heat conduction (Chapter 9)
VI. Forced convection (Chapter 10)
VII. Natural convection (Chapter 11)
VIII. Radiative heat transfer (Chapter 12)
ASEN 3113 Reading Schedule
Date to have read by Pages Subjects
Aug. 31 183-191 thermal res, heat engines, therm eff
Nov 30 Quiz rev; 625-650 thermal radiation, blackbody
Dec 5 651-670 view factor, black/gray surfaces
Dec 7 671-684 radiation shields, temperature
Dec.12 Quiz Heat transfer review
Dec. 14 Quiz and open review
Quick Review• Property Diagrams: We will plot three key variables P, T, and v.
• Each region of the diagram represents a phase or mixture of phases
Pv Diagram• Saturation curves defineboundaries of liquid-vapormixture region.
• Above the critical point,no amount of pressurecan condense the vaporto a liquid
Regions on a Pv Diagram
PT Diagram
• Three curves can be drawn on the PT diagram• Fusion curve (or melting curve)
• Vaporization curve
• Sublimation curve
• The curves bound three distinct regions, one for each phase
• Juncture of the three curves is the triple point where all three coexist
PT Diagram
Other PT Features
• An isobar at standard atmospheric pressureintersects the normal boiling and melting points
• The critical point is on the vaporization curve
• Gas above critical T is called “gas”, below it iscalled “vapor”
PvT Diagram for Water
• The quantity enthalpy, symbolized by H, also calledheat content, is the sum of the internal energy of athermodynamic system plus the energy associated withwork done by the system on the atmosphere which is theproduct of the pressure times the volume.
• The term enthalpy is composed of the prefix en-,meaning to "put into", plus the Greek suffix -thalpein,meaning "to heat".
Enthalpy
The function H was introduced by the Dutch physicistKamerlingh Onnes in late 19th century in the followingform: where E represents the energy of the system.•H is the enthalpy•U is the internal energy, (joule)•P is the pressure of the system, (pascal)•V is the volume, (cubic meter)
• Enthalpy is a quantifiable state function, and the total enthalpy of asystem cannot be measured directly; the enthalpy change of asystem is measured instead.• A possible interpretation of enthalpy is as follows. Imagine we are tocreate the system out of nothing, then, in addition to supplying theinternal energy U for the system, we need to do work to push theatmosphere away in order to make room for the system. Assumingthe environment is at some constant pressure P, this mechanicalwork required is just PV where V is the volume of the system.Therefore, colloquially, enthalpy is the total amount of energy oneneeds to provide to create the system and then place it in theatmosphere. Conversely, if the system is annihilated, the energyextracted is not just U, but also the work done by the atmosphere asit collapses to fill the space previously occupied by the system, whichis PV.
• Enthalpy is a thermodynamic potential, and is usefulparticularly for nearly-constant pressure processes, whereany energy input to the system must go into internal energyor the mechanical work of expanding the system.• For systems at constant pressure, the change in enthalpyis the heat received by the system plus the non-mechanicalwork that has been done. In other words, when consideringchange in enthalpy, one can ignore thecompression/expansion mechanical work. Therefore, for asimple system, with a constant number of particles, thedifference in enthalpy is the maximum amount ofthermal energy derivable from a thermodynamicprocess in which the pressure is held constant.
First Law of Thermodynamics
• The first law of thermodynamics is the application of the conservation ofenergy principle to heat and thermodynamic processes:
• Energy can’t be created or destroyed; it canonly change form.
Internal Energy• Internal energy is defined as the energy associated with therandom, disordered motion of molecules. It is separated inscale from the macroscopic ordered energy associated withmoving objects; it refers to the invisible microscopic energyon the atomic and molecular scale.• For example, a room temperature glass of water sitting on atable has no apparent energy, either potential or kinetic. Buton the microscopic scale it is a seething mass of high speedmolecules traveling at hundreds of meters per second.
Joule, James (1818-1889)
English physicist who was initially interested in theefficiency of electric motors. He discovered the heatdissipated by a resistor is given by Q = I2Rt, a resultnow known as Joule’s law. Motivated by theologicalbeliefs, Joule began attempting to demonstrate theunity of forces in nature. He determined themechanical equivalent of heat by measuringchange in temperature produced by the frictionof a paddlewheel attached to a falling weightin the 1840s. He made a series of measurementsand found that, on average, a weight of 772pounds falling through a distance of one footwould raise the temperature of one pound ofwater by 1° F. This corresponds to (772 ftlbs)(1.356 J/ft lb) = 59 453.6 Calories, or 1 cal =4.15 Joules, in close agreement with the currentaccepted value of 1 cal = 4.184 J. Joule was not thefirst person to establish the mechanical equivalenceof heat, but it was his demonstration that eventuallycame to be accepted. He did not claim, however, tohave formulated a general Law of Conservation ofEnergy. Nevertheless, his experiments werecertainly fundamental in bringing that formulationabout. In addition, Joule's experiments showedthat heat is produced by motion, contradictingthe caloric theory.
German physicist who presented anumerical value for the mechanicalequivalent of heat in 1842, based on ahorse stirring paper pulp in a cauldron.Although his result was published fiveyears before Joules, it was Joule whoclaimed that Mayer's value was nothingbut an unsupported hypothesis, whoreceived credit. Mayer attempted suicide,and was confined for a while to a mentalinstitution. Eventually, Tyndall lecturedon Mayer's work and tried to obtain therecognition he deserved. Mayer claimedthat the "vital chemical process" (nowcalled oxidation) was the ultimate sourceof energy for a living organism.
Mayer, JuliusRobert von (1814-1878)
Heat• Heat may be defined as energy in transit from a high temperature object to alower temperature object.• An object does not possess "heat"; the appropriate term for the microscopicenergy in an object is internal energy.• The internal energy may be increased by transferring energy to the objectfrom a higher temperature (hotter) object - this is properly called heating.
Heat and Work; a closed system
• Interchangeability of heat and work as agents for addingenergy to a system
What if we consider the Earth and itsocean/atmosphere as a closed system?
• What are the heat and work energy exchanges?
• What is the ultimate source of energy for allprocesses on the Earth?
What is an adiabatic process? (No heat exchange.)
What is an isothermal process? (No change in temperature)
What was the caloric theory?
• The caloric theory was introduced by Antoine Lavoisier who haddiscovered the explanation of combustion in terms of oxygen in the 1770s.• Lavoisier argued that phlogiston theory was inconsistent with hisexperimental results, and proposed a 'subtle fluid' called caloric as thesubstance of heat. According to this theory, the quantity of this substance isconstant throughout the universe, and it flows from warmer to colder bodies.• Since heat was a material substance in caloric theory, and therefore couldneither be created nor destroyed, conservation of heat was a centralassumption.• Besides the caloric theory, another theory existed in the late eighteenthcentury that could explain the phenomena of heat: the kinetic theory. Thetwo theories were considered to be equivalent at the time, but caloric theorywas the more modern one, as it used a few ideas from atomic theory andcould explain both combustion and calorimetry.
Caloric Theory
American-British physicist and scoundrel who, while drillingout cannons in the Munich munitions works, noticed that thecanon became hot as long as the friction of boring continued.Furthermore, Rumford observed, the amount of heat releasedwould be sufficient to completely melt the canon if it could bereturned to the metal. Since more heat was being releasedthan could have been originally contained in the metal, theseobservations were an outright contradiction to the calorictheory. Rumford was therefore led to conclude that it was themechanical process of boring which was producing the heat.Rumford even calculated a value of the mechanicalequivalent of heat which, however, was not nearly asaccurate as the one reported later by Joule. Nonetheless,despite the solidity of his results, physicists of his dayignored his work as unconvincing, clinging instead to thecaloric theory of heat as a fluid. It is rather surprising, giventhe great interest in the unity of Nature, that the firstquantitative verification of the convertibility of twoapparently different physical entities was completely ignoredby the entire community. Some degree of hesitancy toabandon the conventional caloric theory would beunderstandable, but disregarding such cogent and basicresults as those produced by Rumford's investigations isdifficult to understand. It was only a matter of time,however, until Rumford's experiments were repeated andimproved by others, eventually leading to the acceptance ofthe equivalence of heat and work.
Rumford, BenjaminThompson (1753-1814)
What are the modes of heat transfer?
• Conduction
• Convection (both free and forced)
• Radiation
We know that work can be converted into heat (ie friction)but what about converting heat into work? We need tobuild a “heat engine” to convert heat into useful work.Problem is that efficiencies are not perfect and we lose bothheat and work in these conversion processes.
Thermal and Energy Reservoirs
• Body with large thermal capacity (can store energy).
• Must be able to store (or supply) finite amounts ofheat/energy without a change in temperature
• Examples: The ocean, the atmosphere, large lakes, etc.
• In practice an example is an industrial furnace. Due tohigh temperatures is can gain and supply heat energywithout a change in temperature.
• With such a “source” we can build a “heat engine.”
• A heat engine performs the conversion of heat energy tomechanical work by exploiting the temperature gradientbetween a hot “source" and a cold “sink".• Heat is transferred to the sink from the source, and in thisprocess some of the heat is converted into work by exploitingthe properties of a working substance (usually a gas or liquid).• The larger the difference in temperature between the hotsource and the cold sink, the larger is the potential efficiency ofthe cycle. On Earth, the cold side of any heat engine is limitedto close to the ambient temperature of the environment, or notmuch lower than 300 Kelvin, so most efforts to improve thethermodynamic efficiencies of various heat engines focus onincreasing the temperature of the source.
The efficiency of various heat engines proposed or used today ranges from3 % (97 % waste heat) for the OTEC ocean power through 25 % for mostautomotive engines, to 35 % for a supercritical coal plant, to about 60 %for a steam-cooled combined-cycle gas turbine.• All of these processes gain their efficiency (or lack thereof) due to thetemperature drop across them.• OTEC uses the temperature difference of ocean water on the surface andocean water from the depths, a small difference of perhaps 25 ° C, and sothe efficiency must be low.• The combined cycle gas turbines use natural-gas fired burners to heat airto near 1530 °C, a difference of a large 1500 °, and so the efficiency canbe large when the steam-cooling cycle is added in.
• A heat engine typically uses energy provided in the form of heat to dowork and then exhausts the heat which cannot be used to do work.Thermodynamics is the study of the relationships between heat andwork.• The first and second laws of thermodynamics constrain the operationof a heat engine. The first law is the application of conservation ofenergy to the system, and the second sets limits on the possibleefficiency of the machine and determines the direction of energy flow.
Heat engines such as autoengines operate in a cyclicmanner, adding energy inthe form of heat in one partof the cycle and using thatenergy to do useful work inanother part of the cycle.
Heat Engine Cycle
Heat Engine Operates between High and Low Temp Res.
Heat Engines all:
1. Receive heat from high temp source (solar, furnace, etc)
2. Convert part of this heat to work (usually as a rotatingshaft)
3. Reject the remaining waste heat to low temperaturesink (atmosphere, ocean, etc)
