Best thermally conductive paste for galvanized steel heat sink?

[shane21]

Using some snap on radiators around galvanized tubes, as seen here...

Those radiators are also galvanized steel, same as the tubes, though
in that photo the tube looks to already be painted.

I need to maximize the thermal conductivity between the two surfaces.

Radiators don't easily move when snapped down, so not looking so much
for an adhesive here, as whatever will best conduct heat between them.

If a consideration, the Delta T at the maximum will be 70F as the temp
inside and outside pipe ranges from 35F to 105F.

Some radiators will also have water flowing by them at < 100 PSIG and
under 15 gpm, if that plays into thermal paste selection to minimize
risk of having it eroding away.

Appreciate any suggestions, thanks!

 

[IRstuff]

What do you mean by "best?"

Your flow and pressure requirements imply a "glue" and not a "paste." What is service life?

Seems to me the go-to answer is a copper-filled or silver-filled epoxy:

http://conductivex.com/Flexible-Cop...ectrically-Conductive-Adhesive-Room-Temp-Cure

However, since water can erode pretty much anything, your service life may be limited. Your best bet might be to form a metal dam around the epoxy joint.

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[shane21]

By "best" I mean, for this application, ideal for maximum galvanized to galvanized thermal conductivity where water passage may be an erosion issue.

I'd qualify it further to add that it needs to be readily commercially available and not exorbitant where only NASA can afford.

I'd assumed that some conductive coatings are better suited for some particular types of metals and environments than are others.

 

[Compositepro]

If this is a "radiator" a galvanized surface is a poor choice, as "shiny silver" means reflective, which is the opposite of a good radiator. These could be worse than doing nothing. And steel is not usually used for heat transfer except at much higher temperatures than you mention.

This type of heat transfer assemble would normally be soldered or brazed to get acceptable heat transfer.

 

[shane21]

Compositepro, 'radiator' may have been poor word choice, it was used here in
the sense of a car radiator, conducting heat exchange between air and water.

It's not a radiator in the sense of radiant heat, reflectance or emissivty.

I'm only interested here in enhancing the conductive heat exchange.

 

[IRstuff]

Short of welding, the epoxy type I cited is the best your'e going to get.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[shane21]

Thanks, IRstuff, been reading up on it...

 

[btrueblood]

Soldering might make a better joint than epoxy.

 

[shane21]

Decided to give this a shot...

http://www.epoxies.com/_resources/common/userfiles/file/70-3812NC.pdf

Thermal Conductivity, W/m-°K 4.5
$100 for a quart w/ hardener

 

[MintJulep]

Braze with a high-silver filler on bare steel parts.

Galvanize the assembly afterwards.

 

[shane21]

btrueblood and MintJulep, I would solder or braze if I could, I know that's better,
but for cost restriction issues and a dozen other moving parts needing attention in
this project, I've had to compromise here and settle for less than best efficiencies.