Thermo, set 2

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Thermo, set 2
2010-03-13 09:45:12
Engineering Thermodynamics

Chemical Engineering
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  1. Simple system
    the effects of motion, viscosity, fluid shear, capillarity, anisotropic stress, and external force fiels are ABSENT
  2. homogeneous substance
    has uniform thermodynamic properties throughout is said to be homogeneous
  3. pure substance
    a homogeneous and invariable chemical composition and may exist in more than on phase. Include, water, mixture of liquid and water vapor, CO2, N2, mixture of gases, etc.
  4. liquids
    molecules are not fixed positions relative to each other, can rotate and translate freely. The intermolecular forces are weaker relative to solids.
  5. solids
    atoms or molecules arranged in three-dimensional patterns
  6. gases
    molecules are far apart from each other and molecular order is nonexistent
  7. compressed liquid
    (subcooled liquid) - not about to vaporize
  8. saturated liquid
    about to vaporize, at temperature when liquid beings to boil
  9. latent heat
    the amount of energy absorbed or released during phase-change process
  10. Superheated state
    Temperature is greater than the saturated temperature for the given pressure, and vapor is NOT about to condense
  11. vacuum cooling
    temperature of chamber is constant until saturation pressure is reached (3.17 kPa at 25 C), then saturation conditions are mainated at progressively lower pressures and correspond to lower temperatures, until desired temp is reached
  12. T-V phase diagram
    property diagram for phase-change process
  13. critical point
    when the saturated liquid and saturated vapor state are identical, phase change is indistinguishable. At temp/pressure above this point, the phase changes are no longer discrete
  14. triple point
    pressure and temperature of a substance exist in three phases of equilibrium
  15. sublimation
    at low pressure (below triple-point), solids evaporate before melting
  16. Work
    energy transfer of force acting through a distnace. Depends on path of process.
  17. Power
    Work over a unit of time (kJ/s, or kW)
  18. Moving Boundary work
    • W > 0: work done by the system (expansion)
    • W < 0: work done on the system (compression)

    • Wb = ∫ P dV
    • Area under PV curve is boundary work
  19. Cycle work
    • net work during a cycle, difference btwn work done by and on the system.
    • Depends on path and end states.
    • Point function: ∫ dP = P - P = 0
    • path functions: ∫dW = ∫ PdV ¹ 0
  20. Internal Energy
    • U total energy (kinetic and potential) in a system
    • Includes chemical bonds, intermolecular attractions, electrons, etc.
  21. heat capacity
    • amount of energy required to increase the temperature of a substance by 1o C (ext. prop)
    • Molar heat capcity; 1 mol by 1o C
    • Specific heat capacity; 1 g by 1o C