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thermodynamics

By naveen4848 Sep 15, 2014 936 Words
UNIFIED ENGINEERING
Lecture Outlines

2000
Ian A. Waitz

THERMODYNAMICS:
COURSE INTRODUCTION
Course Learning Objectives:
To be able to use the First Law of Thermodynamics to estimate the potential for thermomechanical energy conversion in aerospace power and propulsion systems.

Measurable outcomes (assessment method):
1) To be able to state the First Law and to define heat, work, thermal efficiency and the difference between various forms of energy. (quiz, self-assessment, PRS) 2) To be able to identify and describe energy exchange processes (in terms of various forms of energy, heat and work) in aerospace systems. (quiz, homework, self-assessment, PRS)

3) To be able to explain at a level understandable by a high school senior or nontechnical person how various heat engines work (e.g. a refrigerator, an IC engine, a jet engine). (quiz, homework, self-assessment, PRS)

4) To be able to apply the steady-flow energy equation or the First Law of Thermodynamics to a system of thermodynamic components (heaters, coolers, pumps, turbines, pistons, etc.) to estimate required balances of heat, work and energy flow. (homework, quiz, self-assessment, PRS)

5) To be able to explain at a level understandable by a high school senior or nontechnical person the concepts of path dependence/independence and reversibility/irreversibility of various thermodynamic processes, to represent these in terms of changes in thermodynamic state, and to cite examples of how these would impact the performance of aerospace power and propulsion systems. (homework, quiz, self-assessment, PRS)

6) To be able to apply ideal cycle analysis to simple heat engine cycles to estimate thermal efficiency and work as a function of pressures and temperatures at various points in the cycle. (homework, self-assessment, PRS)

Teaching & Learning Methods
1) Detailed lecture notes are available on the web (for viewing and/or downloading). You should download a copy of these and bring them with you to lecture. 2) Preparation and participation will be important for learning the material. You will be responsible for studying the notes prior to each lecture. Several reading

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assignments will be given to help promote this activity (1/3 of participation grade).
3) Several active learning techniques will be applied on a regular basis (turn-to-yourpartner exercises, muddiest part of the lecture, and ungraded concept quizzes). We will make extensive use of the PRS system (2/3 of participation grade). 4) Homework problems will be assigned (approximately one hour of homework per lecture hour). The Unified Engineering collaboration rules apply.

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UNIFIED ENGINEERING
Lecture Outlines

2000
Ian A. Waitz

THERMODYNAMICS CONCEPTS
I.

Thermodynamics (VW, S & B: Chapter 1)
A. Describes processes that involve changes in temperature,
transformation of energy, relationships between heat and work. B. It is a science, and more importantly an engineering tool, that is necessary for describing the performance of propulsion systems, power generation systems, refrigerators, fluid flow, combustion, ....

C. Generalization of extensive empirical evidence (however most thermodynamic principles and can be derived from kinetic
theory)
D. Examples of heat engines
Combustion Heat 

Solar Heat



 Nuclear Heat



 Mechanical Work 
 Electrical Energy 



[ Heat Engine]

[Waste Heat ]
OR

 Mechanical Work 
 Electrical Energy 



[ Heat ]
Waste Heat

Fuel

Air
V1, T1

1. propulsion system

Air + fuel
V2, T2

Fuel
Air

Electricity

2. power generation

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Electricity

Heat

3. Refrigerator

E. Questions:
1. Describe the energy exchange processes in ___________ (fill in the blank, e.g. a nuclear power plant, a refrigerator, a jet engine).
2. Given that energy is conserved, where does the fuel+oxidizer energy that is used to power an airplane go?
3. Describe the energy exchange processes necessary to use electricity from a nuclear power plant to remove heat from the food in a refrigerator. 4. Describe the energy exchange processes necessary for natural gas to be used to provide electricity for the lights in the room you are in.

II.

Concept of a thermodynamic system (VW, S & B: 2.1)
A. A quantity of matter of fixed identity, boundaries may be fixed or movable, can transfer heat and work across boundary but not
mass
Force x distance (work)

System boundary

System boundary

Electrical energy
(work)

Heat (Q)

B. Identifiable volume with steady flow in and out, a control volume. Often more useful way to view devices such as engines
System boundary

m, p1,T1
complex
process

-4-

m, p2,T2

III. Thermodynamic state of a system
A. The thermodynamic state of a system is defined by specifying a set of measurable properties sufficient so that all remaining
properties are determined. Examples of properties: pressure, temperature, density, internal energy, enthalpy, and entropy. B. For engineering purposes we usually want gross, average,
macroscopic properties (not what is happening to individual
molecules and atoms) thus we consider substances as continua -the properties represent averages over small volumes. For example, there are 1016 molecules of air in 1 mm3 at standard temperature and pressure. (VW, S & B: 2.2)

. Intensive properties do not depend on mass (e.g. p, T, ρ, v=1/ρ, u and h); extensive properties depend on the total mass of the system (e.g. V, M, U and H). Uppercase letters are usually used for extensive properties. (VW, S & B: 2.3)

D. Equilibrium: States of a system are most conveniently described when the system is in equilibrium, i. e. it is in steady-state. Often we will consider processes that change “slowly” -- termed quasisteady. (VW, S & B: 2.3-2.4) thermally insulated

copper
boundary

Force

Gas 1
T1

Pressure

Gas 2
T2

Area

1. mechanical equilibrium
(force balances pressure times area)

-5-

Wait

Gas 1
T3

Gas 2
T3

2. thermal equilibrium
(same temperature)

E. Two properties are needed to define the state of any pure substance undergoing a steady or quasi-steady process. (This is an experimental fact!) (VW, S & B: 3.1, 3.3)
1. For example for a thermally perfect gas (this is a good engineering approximation for many situations, but not all (good for p

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