I stumble on an interesting video, maybe someone find it useful on a new AMD build,
Paul's Hardware Can You PASSIVELY COOL a 12-Core Ryzen 9 3900X?
According to the review, it was able to handle it but it downclock on stress test, he doesn't recommend it, but recommends to go with 3700x for it. Remember its a special motherboard as the NoFan95C doesnt support AM4, his board has a special mount.
Passivly cooling a 3900X
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Re: Passivly cooling a 3900X
always fun to test passive cooling for science, and apparently there's enough of a market (or at least enough marketing value) to warrant noctua testing the waters with the behemoth they had at computex. as noted in that thread, though, it seems like you'd probably be better off with a d15 or equivalent and minimum rpm fan(s). it's hard to picture a use case where a truly fanless solution would be better than a.) low speed fans or b.) getting some longer cables and physically moving the computer.
Re: Passivly cooling a 3900X
I'm not even sure about the 3700X in stress test, unless there is a constant flow from a case fan next to it.
At my job I tried to passively cool something as low as an ASIC drawing 15W after 2 hours the radiator was at 50°C with the component at 60°C, and I ended up needing a fan to keep it under 50°C on 21°C ambiant, the fan is doing very very little pressure and flow, but that was necessary. Even the first recommend an i5-9600K + RTX 2070 max to run passively, and we are talking about a m-atx holding an itx with most of the space used as heat-spreader.
At my job I tried to passively cool something as low as an ASIC drawing 15W after 2 hours the radiator was at 50°C with the component at 60°C, and I ended up needing a fan to keep it under 50°C on 21°C ambiant, the fan is doing very very little pressure and flow, but that was necessary. Even the first recommend an i5-9600K + RTX 2070 max to run passively, and we are talking about a m-atx holding an itx with most of the space used as heat-spreader.