ENGR 260 Sections 3'1 3'3

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ENGR 260Sections 3.1 - 3.3
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Pure Substance

• A substance that has a fixed chemical composition
  throughout
• Water
• Air
• Oil and Water???
• Depending on energy level a pure substance can
  exist in different phases.

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Phases of a Pure Substance

• Solid molecules are arranged in a three
  dimensional pattern or lattice that is repeated
  throughout
• Liquid similar structure to solid phase, but
  molecules are allowed to rotate and translate
  freely
• Gas molecular order is non-existent, random
  movement of molecules

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Transition from Solid to Gas Phase
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Phase Change Processes of Pure Substance
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Phase Change Processes of Pure Substance
(continued)
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T-V Diagram Water at Constant Pressure
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Water Liquid Vapor Saturation Curve
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Temp(F) Pressure (psi)
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T-v diagram for Water
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T-v diagram for a pure substance
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P-v diagram for a pure substance
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New Vocabulary

• Sub-cooled liquid or compressed liquid
• Saturated liquid and saturated vapor
• Saturation temperature and pressure
• Latent heat of vaporization
• Superheated vapor
• Quality
• Critical Point
• Triple Point

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P-v for a substance that contracts on freezing
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P-v for a substance that expands on freezing
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The P-T diagram
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Triple Point
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Sublimation
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P-v-T for a substance that contracts on freezing.
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P-v-T for a substance that expands on freezing.
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From Heat and Thermodynamics, 4th Ed., Mark W
Zemansky, McGraw Hill, 1957
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Property Tables

• Enthalpy A combination property
• h u Pv (Internal Energy Flow work)
• Enthalpy of Vaporization hfg
• Specific Volume vf, vg, vfg

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Property Table Example 1

• A piston-cylinder device contains 3 ft3 of
  saturated water vapor at 114.7 psig.
• What is the mass and temperature of the system?

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Property Table Example 2

• A mass of 200g of saturated water is vaporized
  completely at constant pressure of 100 kPa.
• Determine the volume change of the system.
• Determine the amount of energy transferred to the
  water.

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Saturated Liquid-Vapor Mixture

• Quality ratio of the mass of the vapor to total
  mass of the mixture.

• Saturated Steam has a quality of 1 or 100

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Properties during Vaporization

• The properties of saturated liquid are the same
  whether it exists alone or in a mixture with
  saturated vapor
• A saturated mixture can be treated as two
  subsystems
• saturated liquid
• saturated vapor

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Two phase mixtures
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Steam Quality Example 1

• A 100 ft3 rigid tank contains 10 lb of a water
  liquid vapor mixture _at_ 250F.
• What is the mass fraction of the water in the
  vapor phase?

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Steam Quality Example 2

• Determine the enthalpy for a 50/50 liquid-vapor
  mixture at 100 psia.

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Superheated Vapor and Compressed Liquid

• Why does steam delivered from a boiler always
  contains a few degrees of superheat?
• Where do we see compressed liquids in
  engineering?

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Reference States and Values

• Reference State for Water
• Saturated Liquid at 0.01C
• Internal Energy and Entropy are assigned zero
  values at that state.