Heatsink with additional forced cooling

[kekon]

Is there a way to calculate thermal resistance of a heatsink with a fan assembled on it ? (provided we have power dissipated in the heatsink, its geometry and thermal resistance, fan m3/h, ambient temperature etc.).
I thought of carrying out some experiments by try and error method but it doesn't seem to be accurate.

 

[chuckey]

Because of the difficulties in determining where the airflow is actually going (30% more to front left hand , none to back right hand etc.), as you say its a difficult one. Constraining the air to flow through the heat sink would be the most effective. I have seen hi-power heat sinks like a square tube with fins pointing inwards and designed so a fan will fit straight onto its end. Of course it helps if the air has a clear exit too.
Frank

 

[dick_freebird]

Airflow & its distribution can't really be known without fancy setup,
but you should be able to get a temp rise for some level of thermal
power input and that ought to be good enough.

Calculating, I would not bother. The quality of data / quantity of
unknowns is too poor.

 

[keith1200rs]

You could get some idea of the effects of forced air cooling here.

www.nxp.com/documents/application_note/APPCHP7.pdf

Keith

 

[kekon]

Thank you; it's a very useful article. It seems it will be very helpful.