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Old   November 18, 2013, 09:12
Default Natural convection from heatsink
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Hello,

I'm currently simulation natural convection in 3-D from a plate-finned heatsink with multiple heatgenerators.

I use pressure-based solver, with gravity.

  • Energy equation
  • k-epsilon turbulence, with scalable wall fc and full bouancy effects.
  • P1, with emissivity:0,85 on most solids.
i use Simplec with discretizations:
  • standard pressure
  • Second order on the others
as materials there is only air and aluminium


Questions regarding air properties:

  1. How do i best define density for air here? I have used mostly boussinesq approx. Here i wonder what sould i define operating temerature as? (in operating conditions) Should it be my ambient air temperature, or should it be the same temperature as the boussinesq density is defined (in materials) I have also tried incompressible ideal gas with a defined density (in operating conditions) With this it seems to get alot hotter, about 10 degrees...
  2. An is it possible/meaningful to use piecewise polynomial to define thermal conductivity, Cp and viscosity and still get convergence? Or should i define them as constants?
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Old   November 18, 2013, 09:14
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forgot to mention that my deltaT is around 40 degrees at the most, So Ra=laminar.
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