ME 3304 - Ch. 1

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  1. Heat Transfer (Heat)
    Thermal energy in transit due to a SPATIAL temperature difference.
  2. Heat Flux
    The rate of heat transfer in the x direction per unit area PERPENDICULAR to the direction of transfer

    q'' = q / A
  3. variable: k
    Conduction Heat Transfer Coefficient


    Mechanism, Who?, Equation
    Diffusion of energy due to random molecular motion

    • Fourier's Law
    • Heat flux, q'' =

    Mechanism, Who?, Equation
    Same as conduction + energy transfer due to bulk motion

    Newton's Law of Cooling

    q'' = h ( Tsurface - Tfluid )
  6. variable: h
    Convection Heat Transfer Coefficient

    W/(m2 * K)

  7. Advection
    energy transfer due to bulk motion
  8. Convection heat transfer is_______ if transferred TO the surface
    --( Tsurface < Tfluid )
    NEGATIVE heat transfer TO the surface
  9. Convective heat transfer is________ if heat is transferred FROM the surface
    --( Tsurface > Tfluid )
    POSITIVE heat transfer FROM the surface
  10. Forced Convection
    Flow is caused by external means, such as by a fan, pump, or atmospheric winds.
  11. Free (natural) Convection
    Flow is induced by buoyancy forces, which are due to density differences caused by temperature variations in the fluid.
  12. Sensible energy
    Internal thermal energy of the fluid
  13. Latent heat exchange
    associated with a phase change between the liquid and vapor states of the fluid

    Mechanism, Equation

    **occurs most efficiently in a vacuum**
    Energy transfer by electromagnetic waves (or photons)

    • qrad'' = q / A =
    • qrad'' =
  15. variable:
    emissivity variable

  16. Ideal Radiator
    Blackbody: emits radiation at the maximum possible rate

    = 1
  17. variable: Eb
    Emissive Power
  18. Stefan-Boltzmann Law
    = 5.67 x 10-8 W/(m2K4)

    Eb =
  19. Incident Radiation
    may originate from a special source, such as the sun, or from other surfaces to which the surface of interest is exposed.
  20. variable: G


    Irradiation energy = (reflected + transmitted + absorbed) energy
  21. variable:
  22. Gray surface condition?
  23. variable: hr
    radiation heat transfer coefficient

  24. Thermal and Mechanical Energy Equation
  25. Internal energy consists of a:
    1. Sensible component
    2. Latent component
    3. Chemical component
    4. Nuclear component
    • 1. accounts for translational, rotational, and/or vibrational motion of the atoms composing the matter.
    • 2. relates intermolecular forces influencing phase change
    • 3. accounts for energy stored in the chemical bonds
    • 4. accounts for binding forces in the nucleus
  26. Simplify the TME Equation for STEADY STATE conditions.
    Edot stored = 0
  27. Simplified STEADY-FLOW thermal energy equation
    Qdot = q = mdot x Cp x ( Tout - Tin )

    • 1. ideal gas with KE, PE, W = 0
    • 2. incompressible liquid with KE, PE, W = 0
    • OR
    • ideal gas/incompressible fluid with negligible viscous dissipation
  28. Surface Energy Balance
    Edot in - Edot out = 0

    q''cond - q''conv - q''rad = 0

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ME 3304 - Ch. 1
2012-01-12 20:55:14

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