Thermodynamics

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Thermodynamics

• ENTC 370

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Announcements

• Course Syllabus
• Class Webpage
• http//etidweb.tamu.edu/classes/entc370/
• Classnotes in Power Point
• Homework assignments and solutions
• Announcements
• E-learning
• Grades are regularly posted through E-learning
• Labs
• A lab manual will be available for this course
  early next week
• A PDF version will be available on line, just go
  to E-learning
• Lab exercises 50 Computational (EES) 50
  Hands On
• No labs this week

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What is Thermodynamics?

• Is the science of energy
• Deals with energy transformations, including heat
  and work, and the physical properties of
  substances involved in the transformation (Jones
  Hawkins, 1986)
• Conservation of Energy Principle Energy cannot
  be created or destroyed, only transformed
• Thermodynamics is used to describe and understand
  energy systems
• All energy systems are constrained by the laws of
  physics (1st and 2nd Laws of Thermodynamics)
• 1st law of Thermodynamics Expression of
  Conservation of Energy Principle
• 2nd Law of Thermodynamics Energy also has
  quality, energy processes occur in the direction
  of decreasing quality
• Heat flows from Hot to Cold

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Why is Thermodynamics Important?

• Energy affects the World Economy
• Energy is used everyday by everyone
• Depending on the source, it can be renewable or
  non-renewable
• Renewable Wind, Solar, Geothermal, Tidal
• Non-renewable Fossil Fuels (Oil, Coal, Tar,
  Wood), Nuclear Fuel

http//www.eia.doe.gov/oiaf/aeo/figure_2.html
http//www.eia.doe.gov/oiaf/ieo/figure_1.html
http//www.eia.doe.gov/oiaf/aeo/figure_83.html
http//www.eia.doe.gov/oiaf/aeo/figure_95.html
http//www.eia.doe.gov/pub/oil_gas/petroleum/featu
re_articles/2004/worldoilsupply/oilsupply04.html
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How is Energy Transformed, Used and Delivered? ?
Energy Systems
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Energy System Steam Power Plant
http//www.me.utexas.edu/kim/me320/pic/sb-spp.JPG

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Examples of Energy System Boilers
Water-tube boilers
Fire-tube boiler
http//science.howstuffworks.com/
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Example of Energy System Gas Turbine
http//science.howstuffworks.com/
http//www.rolls-royce.com/education/schools/defau
lt.jsp
http//en.wikipedia.org/wiki/Gas_turbine
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Energy System Example Car Engine
http//auto.howstuffworks.com/engine.htm
http//www.dailymotion.com/cluster/tech/video/xk95
2_3d-deutz-engine-animation?fromrss
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Car (Gasoline or Diesel) Engine

• http//auto.howstuffworks.com/engine3.htm
• http//auto.howstuffworks.com/diesel1.htm

Other Engines

• Thermoelectric Direct conversion of thermal
  energy to electricity (Seebeck effect)

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Energy System Example Refrigeration and Air
Conditioning
Refrigeration Units
Air Conditioning Unit
http//science.howstuffworks.com/
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Purpose and Objective

• Understand the key concepts in thermodynamics
  (i.e. laws of thermodynamics, etc.)
• Use of the 1st and 2nd law, system conditions and
  material properties to solve real problems
• Dont want to shoot in the dark
• Used to determine what is possible or impossible
• Learn how to logically and methodically solve
  thermodynamics problems
• Lifelong skills
• known methodology Solution (unknown)

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Thermodynamic SystemsOpen or Closed

• System is
• Quantity of matter or region of space chosen for
  study and analysis
• Surroundings are
• Region outside the system

Surroundings
System
Boundary
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Closed System

• Closed system
• Fixed mass and no mass can enter or leave system
• Energy can cross boundary and boundary can move
  (Example Piston-Cylinder device)

Closed System
No mass transfer
Heat transfer
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A closed system consists of a fixed amount of
mass and no mass may cross the system boundary.
The closed system boundary may move. Examples of
closed systems are sealed tanks and piston
cylinder devices (note the volume does not have
to be fixed). However, energy in the form of
heat and work may cross the boundaries of a
closed system.
Piston-Cylinder Device
Rigid Container
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Open System

• Open system or control volume
• Mass and energy can cross boundary
• Examples Compressors, turbines, and nozzles

Open System
Mass transfer
Heat transfer
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An open system, or control volume, has mass as
well as energy crossing the boundary, called a
control surface. Examples of open systems are
pumps, compressors, turbines, valves, and heat
exchangers.
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Properties

• Intensive properties
• Independent of the size of the system
• Temperature
• Density
• Pressure
• Extensive Properties
• Dependent on system size
• Mass
• Volume
• Total Energy

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Intensive properties are those that are
independent of size. Some Intensive Properties
a. temperature b. pressure c. age d.
color e. any mass independent property
Extensive properties per unit mass are intensive
properties. For example, the specific volume v,
defined as

• Specific Property

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View of Matter in Thermodynamics

• Continuum (Classical) vs. Discrete (Statistical)
• Continuous and homogeneous
• Continuum idealization ? ENTC 370
• No discontinuities in any direction (X, Y or Z)

Discrete
Continuum
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State and Equilibrium

• State
• Condition of a system as specified by the values
  of its properties (e.g.T5.0 C, P1 atm)
• If properties change, the system reaches a new
  state
• Equilibrium
• No unbalanced potential nor driving forces
  present within the system
• System is in equilibrium when experiences no
  changes

P
S2
S1
V
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Equilibrium

• Thermal Equilibrium
• No temperature gradient within the system
• Mechanical Equilibrium
• Pressure does not change at a particular point in
  the system

T2
T1 T2
T1
P2
P1 ? P2 P1 P2
P1
P1 ? f(Time) P2 ? f(Time)
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Thermal Equilibrium
Non-equilibrium ? Equilibrium
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Thermal equilibrium