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Originally Posted by HammerSandwich
Cathar, I once wrote that radiators are pretty efficient at low CFM so you can't gain much without more air. Do you agree? It fits with the PA160's design approach.
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Yes, I agree, but with an explanation/example. The main issue with radiators is that they restrict airflow. Can stick a 100CFM 12cm fan on some densely finned 12cm radiator, and get 30CFM flowing through it, albeit at 99% efficiency. Alternately, can properly design your 12cm radiator, stick a 40CFM fan on it and get 35CFM through it, although at 85% efficiency.
Both will perform about the same, but one uses a fan that's 100x quieter (roughly need 100x40cfm fans to be as noisy as a single 100cfm fan) than the other.
The design of the PA radiator series took the above illustrative example to the extreme, and attempts to balance free-flowing air-flow before falling off an arbitrarily placed "knee" on the efficiency curve. The PA120 line I heavily optimised for 0-60CFM rated fans, with 30-45cfm being the main optimised sweet-spot. The best of the competing 12cm radiators that I measured started to achieve performance parity with around 90cfm rated fans, but many others did not "catch up" until 100-130cfm fannage. At this stage though, it really is just better to have a 120x2 radiator, rather than keep on ramping up fan speeds on a single 120x1 rad.
Being able to achieve a radiator C/W of around bang on 0.05c/w with a single shrouded blowing 45cfm/~22dBA fan on a PA120.1 means that you don't have to live with high noise to have decent radiator performance. Alternately, can use a 120.2, use two of those fans at 7v (for around a combined ~14dBA at a guess), and still enjoy <0.04c/w performance. Run them both at 5v and still get ~0.05c/w cooling performance on a 120.2. If you can hear them (Yate-Loon) at 5v at more than 10cm distance in the middle of the night you're a better man than I, power supplies hum louder than the fans run at.
Disk drives whine at around 20-25dBA.
Combining a PA120.2 with some 7v Yate-Loon's, and an Eheim 1046, with a block that makes good use of it, and for <20dBA can get to within 2-4C of the same CPU temps as your loudest highest performing water-cooling setup.
Noise? Who needs noise?