Any thermal impact after the coating?!
In water, thr cooling factor goes way up. Liquids are much better at absorbing heat than gasses are.
Allowing for the fact that you can cool down the water, and circulate it, means you can overclock the device a lot, without heat becoming a factor.
I don't know thd specifics of the coating, but its -unlikely- that it would change the thermal properties to any degree, and any difference would be dwarfed by the benefit of immersing in a liquid.
- 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
The ones on the plugs/connectors were the usual ones, the one I put on the SBC was thick as I couldn’t find a thin big one, and I was afraid to damage the SBC while applying the heat, so maybe it was the double layer type? But I don’t know.
>how big was the waterproof enclosure?
It was big enough to house the SBC (jetson Nano) and some other components needed for the UUV, not exact size but probably ~20x15cm.
> 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
That’s actually a really smart idea, thanks!! I did have a heatsink (those small ones fit the cpu size) but it was under that heat shrink tube so probably made things worse.
> Assuming you’re not going to crazy depths
We didn’t exceed 50m depth, still I was concerned the pressure might leak some water into the enclosure and this I used the heat shrink.
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.)
You're very likely to destroy it over time, if not immediately.
If the goal is to keep the processor nicely chilled, you’d probably be better off running liquid water over/through the block of ice and then keeping the coated board chilled in the ice water bath. If you’re trying to get below 0C, you should probably keep using a liquid with a lower freezing point instead of having the board frozen in a block.
My kids playing on the Mega VR headset and complaining about it getting hot is one example of my line of thought. Let’s say you have to absorb the heat generated by a given amount of electricity but want to do it in the most weight efficient way possible.
It turns out that regular old water has basically the highest latent heat of fusion at room temperature and pressure, which means a block of ice can absorb more heat by melting than pretty much anything else gram for gram.
What if the VR headset could just freeze itself overnight and then no fans or reliance on dissipating heat into the external environment but instead into the ice.
It’s probably stupid but I do know water is the best know molecule in terms of latent heat of fusion per gram at room temperature and pressure.