Thermal design PPT document
这是我认为最经典的散热设计的文件,不下你会后悔的.
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thermal-design.pdf
Thermal Solution Design
Prepared by C. P. Cheng
Notebook Thermal Design Challenges
Seeking for “Desktop” equivalent processor frequency and features.
Shrinking form factor ( < 35mm is the common design goal).
35 Watts Northwood in a 17.2 mm internal height.
24.5 watts Banias in a 13 mm internal height.
12 watts Banias LV in a 10.2 mm internal height.
Ergonomics(small,low noise,cool to touch).
More effective design cycles.
To achieve long life and more reliable .
How the CPU Heat Dissipation Takes Place
Conduction─Exchange of kinetic energy between molecules.
Radiation ─Heat is simply radiated away form the object through
electromagnetic waves.
Convection ─Heat transfer is driven by movement of a heated or
cooled substance.
Forced Convection
Free Convection
Dimensionless Numbers in Heat Transfer
Reynolds Number = inertia forces / viscous forces
Nusselt Number = convection / conduction
High value of this no. means the heat transfer is enhanced by
convection.
Prandtl Number = momentum diffusivity/ thermal diffusivity
if Pr > 1 means thermal profile develops more rapidly than velocity
profile. For air Pr=0.72 at moderate temperatures.
Grashof Number = buoyancy forces / viscous forces
In free convection the Grashof number plays the same role as
the Reynolds number in force convection.
Rayleigh number = Grashof number * Prandtl number
Nu = C *( Ra )**n
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