Servers are in 4U rack mounted enclosures with (relatively) low height heatsinks and huge amounts of airflow. Intake in front, exhaust in rear. Most clients will have beefy air conditioning to keep the ambient intake temp and humidity low.
I think 4U servers are quite rare these days, except for models designed to accommodate large numbers of either GPUs or 3.5" hard drives. Most 2-socket servers with up to a few dozen SSDs are 2U designs.
Agreed. My last company we used a 1RU with 2 blades (servers) in that space. Front to back cooling, quite loud. No need to worry about the noise in the DC. Power density in a rack vs computer density is all that matters.
