I'd guess that heatsink and a case with heatpipes would be sufficient for most, though perhaps not all, uses and silent, which for me is pretty important on a Raspberry Pi
That's what Apple used to do with their Macbooks. Heat pipes into the metal frame which conducts it over a larger surface area creating natural convections which carry the heat into the air.
The real downside is that mass plays a substantial role. Meaning thicker metal, larger cases, are better than thinner/smaller. Whereas a fan can accomplish similar results for less cost and space (but not passively).
If people don't think passive can work they need to check out Apple's recent Mac Pro that passively cools two Radeon Pro 580Xs. There's no limit, except cost.
Personally I still feel a combination of heat pipe, into heat sink, with a small progressive fan is the ultimate. If it is large enough the fan should stay off except under heavy load.
While there are not extra fans on the cards themselves, I'd hardly call anything in the Mac Pro "passively cooled" considering there are three giant fans on the chassis immediately in front of those heatsinks.
Apple has a pretty long history of passively cooled devices, including the G4 cube, which had a massive (for the time) CPU and GPU, if you wanted in it, was 8 inches cubed in volume, and cooled convectively.
This pretty much lines up with my findings. I popped the pre-installed heat-spreader off and applied a heatsink with noctua thermal paste... basically no difference- step-by-step chaos here: https://twitter.com/Gadgetoid/status/1151442153584910337
Just adding a small fan (trying to avoid blowing our own trumpet too much here) absolutely demolishes the cooling performance of any reasonably-sized heatsink. Presumably there's just not that much passive airflow over something an inch square, even with convection.
I still wonder what would happen if a full desktop-sized heatsink was coupled to the Pi 4's SOC.
I still wonder what would happen if a full desktop-sized heatsink was coupled to the Pi 4's SOC.
In all likelihood, you'd see diminishing returns as you get bigger, but that would be quite the sight to see.
I've been tempted for a while to build a big case with some sort of mounting standard (maybe a Peek array?) so that I can add whatever hardware I want to it (mostly electronics). This seems like a job for that.
I appreciate you actually trying. A "negative" result is still valuable.
What I don't like about the article is that small fan have to spin fast (= noise) to generate enough flow. I'd much rather use a 80 mm fan, slowed way down, but I suppose I'd had to roll my own case for that. Better still, wait for someone to start offering this (or maybe this: http://blog.flirc.tv/index.php/2019/06/24/new-pi-4-cases/)
I'm not the best judge, but these are really quiet fans. I can hear the ones in my laptop, but don't notice Fan SHIM at all. We've had a couple of customers who have, but a replacement fan has been quiet- guessing it's a tolerance issue with the plastics.
convection cooling needs a decent gap between the fins for it to really work. This is why something like Noctua's passive cooler ( https://www.anandtech.com/show/14486/noctua-shows-off-concep... ) looks totally different from their tower coolers with a fan.
Just slapping a normal CPU heatsink on the pi4 will probably work OK just do the thermal mass and exterior surface area of it, but you're probably not going to get much convection-cooling from it, either.
The problem is there are now a number of chips on the board—many of which are too small to pop a heatsink on them—which get crazy hot. If you have the Pi inside any kind of enclosed case, that heat just bakes everything else, even if you have heat sinks.
You could design a copper heat-spreader to pop over the heat-sensitive part(s) of the board, and then apply a heatsink to that. Maybe copper foil would do the job.
Another approach is to just run the Pi submersed in mineral oil, with liquid convection then taking the heat away from the board and shedding it to the surrounding environment. We usually don't run our electronics like this (even though the general approach is widely used for cooling needs of all sorts) because mineral oil is gross and might even impact the endurance of our hardware - but the Pi is tiny and cheap enough to make this a non-issue.
