Liquid cooling baseline testing

George H.

Another design challenge is where I'm going to find a miniature "No Fishing" sign with the right geometry to fit thru the fill port opening of the coolant reservoir...

Why thermal epoxy and not solder?

seems unlikely that it would unlikely to outperform metal.

I've hand-soldered a couple small brass parts together with 60/40 to make some custom plumbing fittings for this project (regular electronics solder and a ~50 watt iron works great for small brass pieces.)

I've brazed some copper pipe before but...basically I don't have any experience soldering (welding?) large parts of dissimilar metals like that together. The enclosure itself is small, a bit delicate and awkward to fit a clamp or clamps into.

Essentially I feel it will probably be a pain in the ass for me to do it well on the first try as compared to the epoxy, most likely result is a moderately costly screwup. :(

This box is kind of a "labor of love" at this point anyway I'm not turning a big profit on it as is sometimes the case when you have clients who work in "the arts."

Those copper heatsinks are kinda expensive - copper is expensive!

soldering aluminium is not quite impossible but close nough

Huh, well I'm no expert either, but it's mostly a matter of getting everything to the right temperature. For your type of things it looks like a hot plate would be a great help. Tin both sides, heat and squish together, scrap off excess solder that runs out the edges, and let cool.

As far as screwing up, you've got to get some other pieces to practice with first. A hot plate and propane blow torch. If one side breaks it's easier to take apart than epoxy. George H.

led

With the right flux it's easy...

George H.

If it matters the chassis is anodized and brushed finished, the interior of it as well, it's a very slick surface

led

cs

rd

it

Yes. if you wanted to try solder and Al ya gotta sand off the anodization. Otherwise some thermal grease and squeeze hard. I've never used thermal epoxy.

George H.

It'll turn into a pretzel due to differential thermal expansion as it cools.

It doesn't, except from a dimensional stability and residual stress point of view.

Cheers

Phil Hobbs

Arctic Silver epoxy is pretty good. Several W/m/K.

Cheers

Phil Hobbs

Hmm a relatively thick layer of the 'right' TCE alloy. I have no idea if such solders exist.

George H.

If you want best heat transfer, the water/copper/epoxy/aluminum is no improvement over water/aluminum. Corrosion might be an issue (not all Al alloys are good when wet, and Cu with Al is a corrosion issue).

Aluminum castings with embedded pipes are not unknown (Cray-1 used those).

I'd consider putting a soft copper tube into an aluminum channel, then pulling a ball bearing through the bore to swage it into good contact. Brute force is cheaper than fancy adhesives.

if you want to improve it you need to now the temps at each point in the heat transfer path. Otherwise you're just guessing where the main resistance is.

NT

It's a counsel of perfection. If you do know the temperature between each of the elements separated by your various thermal resistances, then you can work out what each one of them is, if you know the heat flows precisely enough.

In reality, you can estimate thermal resistances fairly accurately, which is to say guess, accurately enough.

It is a good idea to know how hot your heat-sink gets, but drilling thermistor wells all over the place is rarely worth the trouble.

I was curious as to how well something like propylene glycol compared to water as a coolant fluid but couldn't immediately find any data...

Antifreeze is usually diluted using water. water has a higher thermal capacity also it flows much more freely. glycol is viscous.

Appaently noone considers using pure glycol as a coolant.