Sections 1'11'5

1
Sections 1.1-1.5

• Engr 260 Thermodynamics

2
Early Thermodynamics

• What is Thermodynamics?
• therme (heat)
• dynamis (power)
• Classically thermodynamics was defined as the
  conversion of heat to power
• Early steam engines
• Built in late 1600s/early 1700s
• Very inefficient

3
Early Thermodynamics
4
Thermodynamics and Energy

• Today thermodynamics is more broadly interpreted
  to include all aspects of energy and energy
  transformations
• Power generation
• Refrigeration
• Heating Systems
• Air conditioning
• Solar Systems
• Hot water heaters

5
Thermodynamics and Energy Power Generation
6
Thermodynamics and Energy Refrigeration
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Thermodynamics and Energy Heating Systems
8
Thermodynamics and Energy Air Conditioning
Systems
9
Thermodynamics and Energy Solar Systems
10
Thermodynamics and Energy Hot Water Heaters
11
First Law of Thermodynamics

• Conservation of Energy during an interaction
  energy can change from one form to another, but
  the total amount energy remains the same
• Or energy can neither be created nor destroyed,
  it can only change forms.

12
First Law of Thermodynamics

• Examples of the conservation of energy
• electricity can be converted to heat
• heat will boil water and make steam
• steam will push a piston (mechanical energy) or
  rotate a turbine that makes electricity
• What are more examples?

13
Classical and Statistical Thermodyanics

• Classical Thermodynamics
• Macroscopic approach
• Does not require knowledge of behavior of
  individual molecules
• Statistical Thermodynamics
• Microscopic approach
• Looks at average behavior of large groups of
  molecules.

14
Second Law of Thermodynamics

• Energy has both quality and quantity.
• Heat flows from hot to cold.
• Energy spontaneously tends to flow only from
  being concentrated in one place to becoming
  diffused or dispersed and spread out

15
Second Law of Thermodynamics

•  All types of energy spread out like the energy
  in that coffee cup does (unless somehow they're
  hindered from doing so)
• electricity in a battery
• lightning, wind from a high pressure weather
  system
• air compressed in a tire
• water or boulders that are high up on a mountain
• your car's kinetic energy when you take your foot
  off the gas.
• What are more examples?

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Control Volumes and Systems

• System a quantity of matter of region or space
  chosen for study.

• Systems may be open or closed.

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Closed Systems

• Closed system or control mass mass is not
  allowed to cross the system boundary.
• Isolated system no energy crosses boundary

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Open Systems

• Open System or control volume both mass and
  energy are allowed to cross the system boundary

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Examples

• Closed Systems
• Pressure Cooker
• Ideal Gas Experiment
• Greenhouse

• Open Systems
• Radiator
• Hot Water Heater
• Steam Nozzle
• Steam Pressure Reducing Valve

20
Dimension and Units

• Metric System
• English System
• Primary Units Secondary Units
• Mass (m) - velocity (l/t)
• Length (l) - force (m.l/sec2)
• Time (t) - volume (l3)
• Temperature (T)

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Units of Measure
These units are related by Newtons Second Law
F ma newton and lbm are secondary units
22
Unity Conversion Factors

• Metric System
• English System

which is rewritten as
which is rewritten as
23
Weight of a particle

• SI or Metric
• g local gravitational constant
• g 9.807 m / sec2
• US Customary
• g 32.174 ft / sec2

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Weight of a Unit Mass at Sea Level
W mg
W mg
25
Weight of a Unit Mass at Sea Level
26
Dimensional Homogeneity

• Terms of a equation must have the same units
• If not, I know that I made a mistakeself-checking
  .
• Free Fall Equation

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Example

• A 2 m3 tank is filled with a liquid whose density
  is 850 kg/m3. Determine the mass of the liquid
  in the tank.

28

• I was watching cartoons on Saturday morning. I
  had just purchased a new "device" on eBay to
  measure the speed of cartoon characters as they
  ran by on the television screen in hope to answer
  an age old question
• "Who was faster Mighty Mouse, Speedy Gonzalez or
  Road Runner?"
• Road Runner 120 ft / sec
• Mighty Mouse 2000 m / min
• Speedy Gonzalez 80 miles / hour

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Properties of Systems

• Property a characteristic of a system
• Intensive Property Properties that are
  independent of the mass of the system
• (usually lower case)
• Extensive Property Properties that are
  dependent on the mass of the system
• (usually UPPER case)
• Specific Property Properties that are per unit
  volume of mass

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Property Examples

• Intensive
• Temperature, T
• Pressure, P
• Density, ?

• Extensive
• Volume, V
• Mass, m

• Specific
• Specific Volume, v
• (Volume/mass)
• Specific Energy, e
• (Energy/mass)

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Density and Specific Volume

• Density mass per unit volume
• Specific Volume volume per unit mass

32
Gas Density

• Density is proportional to pressure and inversely
  proportional temperature
• Ideal Gas Law

33
Liquid Density

• Most liquids are incompressible, so density
  varies little with pressure
• Most liquids do however vary in density with
  temperature
• Water density
• You can usually assume
• liquid density is constant
• without losing much accuracy.

34
Specific Gravity

• Specific gravity
• Ratio of density of a substance to a standard
  density
• Standard density is usually water at 4oC
• Dimensionless
• Density of water at 4oC is 1 g/cm3 1 kg/L
  1000 kg/m3
• Note that specific gravity of water (at 4oC) is 1