asen 3113 thermodynamics and heat transfer t, th 12:30-1:45 pm (eccr 200) friday 8:00-9:50, 10-11:50...

ASEN 3113Thermodynamics and Heat Transfer

T, Th 12:30-1:45 pm (ECCR 200)Friday 8:00-9:50, 10-11:50 (ITLL and ECCR 200)

Instructors: William Emery Dax MatthewsECME 275 ECEN 218A (in the back)[email protected] [email protected]

303-492-8591 303-492-1308Office hours: T, Th 2-3 pm T, Th 2-3 pm

LabCoordinator: Trudy SchwartzOffice: ECASE 1B44303-735-2986

TA’s Kevin Higdon Andrew [email protected] [email protected]

ECAE 131 ECAE 131

Office hours: M, W, F 1-2 pm

CA Matthew Osborn

Text: Y.A. Cengel, Introduction to thermodynamics and heat transfer, Irwin/McGraw-Hill, 1977

• This course follows ASEN 2002 and covers the Second Law of Thermodynamics, Entropy, Power/Energy Cycles and Heat Transfer (conduction, convection and radiation).

• The emphasis will be on understanding the basic physical principles associated with these topics and developing the student’s ability to solve numerical problems associated with them.

• Experiments will be carried out to help the student gain experience with the systems representing these principles.

Course Objectives

Given regular class attendance, reading of assigned text material in preparation for quizzes, careful and comprehensive completion of all assignments, students should be able to:

(1) understand the general concepts of thermodynamics and heat transfer in order to develop an intuitive grasp of the subject matter;

(2) develop an ability to apply these basic concepts to engineering design problems.

Course Structure

• The textbook will be followed closely but additional material will be introduced to broaden a particular subject.

• Students are expected to read the assigned textbook section in time to prepare for both in class discussion and for quizzes given approximately every other week.

• Homework assignments will be bi-weekly and will be due on Tuesday of each following week.

• There will be 3 hour-long exams (the lowest score will be dropped in computing the final grade) and a final exam. All exams will be in-class and cover the material between it and the last exam. Exams may require tables and calculation so please bring your books and calculators to class.

• All quizzes and exams will be open book and notes (but not open neighbor). Exams can be made up for valid and proven emergencies (illness, etc.).

• After the quizzes and exams are graded and returned we will go over them to resolve any issues that were particularly problematical to the class.

• If you have any particular difficulty with a question or topic please write it down and submit in written form (hardcopy or email) so that we can go over it in class. You can also bring it up in class. In this way the whole class can benefit from the discussion of problem topics.

• If you have complaints about the class please print it out and submit it anonymously by slipping it under my door when I am out (door is closed). I would prefer to improve the class experience rather than finding out later when I can’t make any changes.

Class Participation

• Class participation is strongly encouraged to both discuss the text material and to respond to quiz and exam questions. Students are encouraged to ask constructive questions and to contribute appropriate comments.

• We are all working together to learn this material and your viewpoint of how you learned the material is very important to the class. (I realize that this is NOT your favorite class so I hope we can work together to make it more interesting for all of 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 and presentation)

* A large percentage is assigned to the homework and lab work.

Office Hours

• You are strongly encouraged to make good use of the office hours set aside for this class and of the TAs. These times are allocated for your benefit.

• If you are unable to come during office hours special arrangements can be made by making an appointment with either instructor or the TAs. It should be remembered that these instructors are busy with other classes and research projects.

• Please use email communications for both instructors and the TAs.

Other Course Policies

• It is the student’s responsibility to read assigned text chapters to prepare for class discussions and unit quizzes. Students are expected to do their own work during quizzes and exams and no communications between students will be allowed.

• We are all responsible for creating a respectful classroom where we can all learn the material at hand. If you do not wish to learn the material you are encouraged to drop the class early in the semester.

Syllabus for ASEN 3113: Thermodynamics of and Heat 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

Sep. 5 Quiz 192-198 2nd law Kelvin, heat pumps, 2nd law Clausius

Sep 7 Quiz and problem review, misc lecture

Sep 12 199-210 revers proc, non-equilib, Carnot cyc

Sep 14 210-221 thermo T scale, carnot ref and ht pump

Sep 19 Exam 1

Sep 21 237-248 entropy, ent increase, ent bal, ent gen

Sep 26 Quiz 249-267 ent, T-s diag, isentropic proc, revers proc

Sep 28 Quiz and problem review, misc lecture

Oct 3 283-296 power cycles, carnot cycle, otto cyc

Oct 5 297-310 diesel cycle, brayton cycle

Oct 10 Quiz 311-320 ideal jet, carnot vapor cyc, rankine cyc

Oct 12 Quiz rev; 321-346 Rankine, efficiency, refrig and ht pmp

Oct 17 Exam 2

Oct 19 375-392 steady ht condc, thermal conduc, insulation

Oct 24 Quiz 393-414 plane walls, thermal resistance, thermal

Oct 26 Quiz and problem review; misc lecture

Oct 31 414-435 radius of def, finned surfaces,

Nov 2 465-483 transient ht conduc, lumped sys

Nov 7 484-496 semi-inf solids, multi-dimen sys

Nov 9 Exam 3

Nov 14 513-533 forced conv, boundary layers

Nov 16 534-557 flow in tubes

Fall break and Turkey Day

Nov 28 Quiz 579-590 free convection, thermal conduc, finned surfaces, effective therm conduc

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 define boundaries of liquid-vapor mixture region.

• Above the critical point, no amount of pressure can condense the vapor to 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 pressure intersects the normal boiling and melting points

• The critical point is on the vaporization curve

• Gas above critical T is called “gas”, below it is called “vapor”

PvT Diagram for Water

• The quantity enthalpy, symbolized by H, also called heat content, is the sum of the internal energy of a thermodynamic system plus the energy associated with work done by the system on the atmosphere which is the product 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 physicist Kamerlingh Onnes in late 19th century in the following form: 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 a system cannot be measured directly; the enthalpy change of a system is measured instead.

• A possible interpretation of enthalpy is as follows. Imagine we are to create the system out of nothing, then, in addition to supplying the internal energy U for the system, we need to do work to push the atmosphere away in order to make room for the system. Assuming the environment is at some constant pressure P, this mechanical work required is just PV where V is the volume of the system. Therefore, colloquially, enthalpy is the total amount of energy one needs to provide to create the system and then place it in the atmosphere. Conversely, if the system is annihilated, the energy extracted is not just U, but also the work done by the atmosphere as it collapses to fill the space previously occupied by the system, which is PV.

• Enthalpy is a thermodynamic potential, and is useful particularly for nearly-constant pressure processes, where any energy input to the system must go into internal energy or the mechanical work of expanding the system.

• For systems at constant pressure, the change in enthalpy is the heat received by the system plus the non-mechanical work that has been done. In other words, when considering change in enthalpy, one can ignore the compression/expansion mechanical work. Therefore, for a simple system, with a constant number of particles, the difference in enthalpy is the maximum amount of thermal energy derivable from a thermodynamic process in which the pressure is held constant.

First Law of Thermodynamics

• The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:

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• Energy can’t be created or destroyed; it can only change form.

Internal Energy

• Internal energy is defined as the energy associated with the random, disordered motion of molecules. It is separated in scale from the macroscopic ordered energy associated with moving objects; it refers to the invisible microscopic energy on the atomic and molecular scale.

• For example, a room temperature glass of water sitting on a table has no apparent energy, either potential or kinetic. But on the microscopic scale it is a seething mass of high speed molecules traveling at hundreds of meters per second.





Joule, James (1818-1889)

English physicist who was initially interested in the efficiency of electric motors. He discovered the heat dissipated by a resistor is given by Q = I2Rt, a result now known as Joule’s law. Motivated by theological beliefs, Joule began attempting to demonstrate the unity of forces in nature. He determined the mechanical equivalent of heat by measuring change in temperature produced by the friction of a paddlewheel attached to a falling weight in the 1840s. He made a series of measurements and found that, on average, a weight of 772 pounds falling through a distance of one foot would raise the temperature of one pound of water by 1° F. This corresponds to (772 ft lbs)(1.356 J/ft lb) = 59 453.6 Calories, or 1 cal = 4.15 Joules, in close agreement with the current accepted value of 1 cal = 4.184 J. Joule was not the first person to establish the mechanical equivalence of heat, but it was his demonstration that eventually came to be accepted. He did not claim, however, to have formulated a general Law of Conservation of Energy. Nevertheless, his experiments were certainly fundamental in bringing that formulation about. In addition, Joule's experiments showed that heat is produced by motion, contradicting the caloric theory.



German physicist who presented a numerical value for the mechanical equivalent of heat in 1842, based on a horse stirring paper pulp in a cauldron. Although his result was published five years before Joules, it was Joule who claimed that Mayer's value was nothing but an unsupported hypothesis, who received credit. Mayer attempted suicide, and was confined for a while to a mental institution. Eventually, Tyndall lectured on Mayer's work and tried to obtain the recognition he deserved. Mayer claimed that the "vital chemical process" (now called oxidation) was the ultimate source of energy for a living organism.

Mayer, Julius Robert von (1814-1878)



Heat• Heat may be defined as energy in transit from a high temperature object to a lower temperature object.

• An object does not possess "heat"; the appropriate term for the microscopic energy in an object is internal energy.

• The internal energy may be increased by transferring energy to the object from a higher temperature (hotter) object - this is properly called heating.



Heat and Work; a closed system

• Interchangeability of heat and work as agents for adding energy to a system

What if we consider the Earth and its ocean/atmosphere as a closed system?

• What are the heat and work energy exchanges?

• What is the ultimate source of energy for all processes 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 had discovered the explanation of combustion in terms of oxygen in the 1770s.

• Lavoisier argued that phlogiston theory was inconsistent with his experimental results, and proposed a 'subtle fluid' called caloric as the substance of heat. According to this theory, the quantity of this substance is constant throughout the universe, and it flows from warmer to colder bodies.

• Since heat was a material substance in caloric theory, and therefore could neither be created nor destroyed, conservation of heat was a central assumption.

• Besides the caloric theory, another theory existed in the late eighteenth century that could explain the phenomena of heat: the kinetic theory. The two theories were considered to be equivalent at the time, but caloric theory was the more modern one, as it used a few ideas from atomic theory and could explain both combustion and calorimetry.

Caloric Theory



American-British physicist and scoundrel who, while drilling out cannons in the Munich munitions works, noticed that the canon became hot as long as the friction of boring continued. Furthermore, Rumford observed, the amount of heat released would be sufficient to completely melt the canon if it could be returned to the metal. Since more heat was being released than could have been originally contained in the metal, these observations were an outright contradiction to the caloric theory. Rumford was therefore led to conclude that it was the mechanical process of boring which was producing the heat. Rumford even calculated a value of the mechanical equivalent of heat which, however, was not nearly as accurate as the one reported later by Joule. Nonetheless, despite the solidity of his results, physicists of his day ignored his work as unconvincing, clinging instead to the caloric theory of heat as a fluid. It is rather surprising, given the great interest in the unity of Nature, that the first quantitative verification of the convertibility of two apparently different physical entities was completely ignored by the entire community. Some degree of hesitancy to abandon the conventional caloric theory would be understandable, but disregarding such cogent and basic results as those produced by Rumford's investigations is difficult to understand. It was only a matter of time, however, until Rumford's experiments were repeated and improved by others, eventually leading to the acceptance of the equivalence of heat and work.

Rumford, Benjamin Thompson (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 to build a “heat engine” to convert heat into useful work. Problem is that efficiencies are not perfect and we lose both heat 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 of heat/energy without a change in temperature

• Examples: The ocean, the atmosphere, large lakes, etc.

• In practice an example is an industrial furnace. Due to high temperatures is can gain and supply heat energy without a change in temperature.

• With such a “source” we can build a “heat engine.”

• A heat engine performs the conversion of heat energy to mechanical work by exploiting the temperature gradient between a hot “source" and a cold “sink".

• Heat is transferred to the sink from the source, and in this process some of the heat is converted into work by exploiting the properties of a working substance (usually a gas or liquid).

• The larger the difference in temperature between the hot source and the cold sink, the larger is the potential efficiency of the cycle. On Earth, the cold side of any heat engine is limited to close to the ambient temperature of the environment, or not much lower than 300 Kelvin, so most efforts to improve the thermodynamic efficiencies of various heat engines focus on increasing the temperature of the source.

The efficiency of various heat engines proposed or used today ranges from 3 % (97 % waste heat) for the OTEC ocean power through 25 % for most automotive 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 the temperature drop across them.

• OTEC uses the temperature difference of ocean water on the surface and ocean water from the depths, a small difference of perhaps 25 ° C, and so the efficiency must be low.

• The combined cycle gas turbines use natural-gas fired burners to heat air to near 1530 °C, a difference of a large 1500 °, and so the efficiency can be large when the steam-cooling cycle is added in.



• A heat engine typically uses energy provided in the form of heat to do work and then exhausts the heat which cannot be used to do work. Thermodynamics is the study of the relationships between heat and work.

• The first and second laws of thermodynamics constrain the operation of a heat engine. The first law is the application of conservation of energy to the system, and the second sets limits on the possible efficiency of the machine and determines the direction of energy flow.

Heat engines such as auto engines operate in a cyclic manner, adding energy in the form of heat in one part of the cycle and using that energy to do useful work in another 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 rotating shaft)

3. Reject the remaining waste heat to low temperature sink (atmosphere, ocean, etc)

4. Operate on a cycle

5. Employ a working fluid

boiler

condenser

pump turbine

Qin

Qout

Compress toboiler pressure Wout

Wnet = Wout - Win = Qin - Qout

asen 3113 thermodynamics and heat transfer t, th 12:30-1:45 pm (eccr 200) friday 8:00-9:50, 10-11:50...

Documents

class experience

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regular class attendance

hourlong exams

heat transfer t

heat transfer conduction

assigned text material

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