Heat-transfer across screw threads

I am likely to mount a 5W luxeon, running at 3W, on a 30mm diameter disc of aluminium 5mm thick and threaded around the edge to screw into a barrel.

I am unlikley to do this if I cannot get most of the heat out through the thread.

Does anyone know if there is a way to calculate temperature drop across a thread.

Has anyone tried anything similar?

Will filling the thread with zinc oxide paste help much?

Thanks to all

Steve

[ QUOTE ]
Bandgap said:
I am likely to mount a 5W luxeon, running at 3W, on a 30mm diameter disc of aluminium 5mm thick and threaded around the edge to screw into a barrel.

I am unlikley to do this if I cannot get most of the heat out through the thread.

Does anyone know if there is a way to calculate temperature drop across a thread.

Has anyone tried anything similar?

Will filling the thread with zinc oxide paste help much?

Thanks to all

Steve

[/ QUOTE ]
I have worked on this very problem before. Here is the short answer.
Without adding heat transfer compound, this type of joint can have high resistance to heat transfer. Adding a heat transfer compound can help a great amount. I would suggest a higher conductivity compound than zinc oxide paste. The other consideration is the size of the gap [thread clearance]being filled. The smaller the better.
Yes, you can calculate the temperature drop if you know the following: the total area of the joint, the average gap distance of the joint, the thermal conductivity of the joint compound, and the rate of heat flow.