Natural convection from heatsink
 

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?

forgot to mention that my deltaT is around 40 degrees at the most, So Ra=laminar.