We saw a Pi running underwater at CES in Las Vegas

> What does ROV stand for?

My apologies for an acronym. It's Remote operated underwater vehicle: https://en.wikipedia.org/wiki/Remotely_operated_underwater_v... (a small submarine, usually, with a long thin tether)

I'm guessing remote operated vehicle - e.g., remote controlled submarines.

If you pull the plug, you break the seal. Water will be able to make contact with the connectors and create shorts between the signals.

I considered digressing into this in my post, but while completely true, I concluded its also irrelevant to the point being discussed. Even tap water has sufficient contaminants to make it an excellent conductor.

Outside of very clean, very lab, conditions, water conducts really well.

But your point is a nice aside, and I'm glad you brought it up.

Incidentally -drinking- pure distilled water tastes funny.

Once you have your ultra pure water, and are willing to commit to maintaining the apparatus that keeps it that way. There is a second problem, extremely pure water is surprisingly corrosive, A laymans explanation is that it would be happier with a few ions, and will gleefuly strip them off any exposed metal.

Which is a shame. It would be nice if water could be used directly in an immersion environment. Much better thermal properties than anything else, and no mess,

Electronic are dirty, your keyboard has a lot of junk, even salt from chips and pretzels, sugar from sticky fingers, etc. Spilling even distilled water on your keyboard dissolves all of that and makes the water conductive. Luckily some better laptops have channels (drip holes) for water to drain without affecting the board, but relying on bad conductivity of distilled wated in real-life scenarios is really not safe :)

Even ultrapure water conducts electricity. It says right here [1] that its resistivity is 1.82×10^9 Ohm * m.

This is a pet peeve of mine. We get told of conductors and insulators in school, but it doesn't work like that. Pretty much everything except a perfect vacuum conducts electricity. It's just that some materials conduct electricity so poorly that it can be rounded off to 0 in most circumstances, but there can still be measurable current flow.

[1] https://en.wikipedia.org/wiki/Electrical_resistivity_and_con...

Getting it that clean is hard. There's stuff like residual flux under the ball grid arrays and other surface mount components.

I’m curious about multiple things!

- what kind of heat shrink was it? There’s the usual thin plastic type and the gooey double-layer type. I’m actually not sure which one would be worse for heat… the gooey type seems like it’d be a thermal insulator but maybe with that much close contact it might be a decent thermal conductor. The regular thin plastic type would probably have been trapping a bunch of air around the heatsink (dramatically reducing the surface area for convection)

- how big was the waterproof enclosure? The stagnant air inside there seems like it would probably heat up pretty well. If the enclosure was plastic it would probably conduct that heat into the water quite poorly.

If you end up in a similar situation down the road, you’re probably way better off making an aluminum plate with a raised pad that you can mount the CPU to directly and use a gasket to allow the outside of the aluminum to conduct the heat directly into the water. Assuming you’re not going to crazy depths I’d expect that to be viable and you’ll probably get “better than forced air” performance out of it

I agree, numbers would be interesting.

My guess is that the effect in air is minimal, because the coating is so thin.

If the coating had impressive thermal properties (such a steep thermal gradient) , even at such tiny thickness, it would have other applications (where thermal insulation is desired.)

Yes. Freeze/thaw cycles are _remarkably_ destructive though. Water expands with insane pressure if it gets caught in any little cavities or grooves.

You're very likely to destroy it over time, if not immediately.