Why does a shroud work so well?
 

I'm curious - why exactly does a shroud work so well? The main reason i can think of is that it minimizes the dead spot of the fan, which is admittedly pretty big for a 120mm.

Does it also reduce noise? Are there any other reasons it helps? How much % temperature difference can one reasonably expect with a shroud?

Also, is a situation where a shroudless setup would work better than one with a shroud possible?

In addition, what is the point of diminishing returns with a shroud - how far away or how near can it keep the fan before it starts becoming a problem?

Thanks :cool:

I think you pretty much answered your own question. But to expand, it not only eliminates (well not totally) the dead spot in the middle of the fan, but it also makes use of more of the area on the rad other than the 120mm circle (or whatever size fan).

Noise decreses as the air is spread out over the entire rad as opposed to the same amount in a smaller area.

Temperature drops are very marginal. I havn't noticed anything over .5C drop with a shroud. I think it would make a larger difference on smaller radiators though.

I don't know about your last question. I just guess. I usually just go 1.5 times the width of the fan body. Not scientific, but seems to work. But then again if real numbers where crunched maybe my .5C would be greater? My water temps are pretty low so I really don't worry about it much.

Hmm, so hasn't anybody crunched some numbers yet?

This looks interesting. I might do it as a physics project for my own benefit. :D