Der8auer on YouTube has experimented with passively cooling an Intel i9-9900K with the ARCTIC Alpine 12; a passive CPU cooler. The ARCTIC Alpine 12 is only rated to handle 47 watts so Der8auer wasn't expecting much out of the unit. Although the passive cooler showed that it was more capable than its rating, it couldn't keep the Intel i9-9900K properly cooled at stock settings. The Intel chip was throttling, so Der8auer ended up with a stable 3.6 GHz clock speed across all cores which was more than capable of playing games on the system. I think we could go even higher to 3.8 GHz @0.975 V. Yes, you can actually passively cool a 9900K with some kind of adjustments. You have to undervolt your CPU a little bit; underclock your CPU a little bit.