Fans, Shrouds, and Radiators OH MY!

[Stang_Man]

ok, i've been pondering about this for awhile, without even trying it, as i don't have anything setup currently.

when people use a shroud with a radiator, are they elevating their fan above the radiator so it doesn't physically touch? the advantages to this would be, less noise, and eliminating the dead spot from the fan motor.

if we let the fans sit directly on the radiator pulling air through the radiator and out the fan (sucking), you would be almost creating a vaccum type effect on it. disadvantages: louder, dead spot from fan motor is taking up space on the radiator fins, and what is the advantage?

i think, that since the fans sit directly on the radiator, more air would pull up through it and would be more turbulent, instead of using a shroud to try to get rid of that dead spot...

don't you think? it's logical, and i think would probably only pertain to sucking air through a radiator, and not pushing air through. when pushing air through, that is when a shroud could be most useful.

speculation: fans sitting directly on top of a radiator, sucking air through it, performs better than using a shroud in which the fans are elevated above.

[gkiing]

Interesting idea, but I have to doubt it because so many people use shrouds.. i'll give it a go on my bonneville core though, maybe post some temps with and without a shroud.

[BillA]

read some on the subject
suggest Fan Engineering by Buffalo Forge

1/2 the fan diameter is a good shroud depth

[DrMemory]

The main reason for using a shroud is to eliminate the dead spot. On a 120mm fan, about 15% of the actual fan area is the motor. Surprisingly, on some 80mm and 90mm fans the motor is not much smaller than the 120 mm fan and take up about 27% of the fan area!. This is a pretty significant dead spot. I've seen any between 1/2" and 1 1/2" suggested for the standoff between the fan and radiator (mine's at 1"). I'd like to see some real numbers on the differences between shrouded and unshrouded fans, as well as the difference between different standoff distances.

[Titan151]

[quote=Stang_Man]i think, that since the fans sit directly on the radiator, more air would pull up through it and would be more turbulent, instead of using a shroud to try to get rid of that dead spot...
QUOTE]

[Titan151]

I think the only thing about a shroud is it eliminates the dead zone. I would also say that there is no benifit to having the fan closer to the radiator vs. being further away. Either way the air it "sucks" will have to go through the radiator. Assuming the shroud is somehwat sealled. I could see that a fan closer to the rad may create more turbulance and or noise, but I doubt that it would make much of a difference.

Here is what you can do to take a look at the air flow. Get your rad and build yourself a plexglass shroud. Then smoke up a cigar and use the smoke to inspect the airflow using multiple configurations. Don't like cigars? Then try using something else.

[BillA]

Titan151
your thoughts are w/o much value, study some

Originally Posted by unregistered

read some on the subject
suggest Fan Engineering by Buffalo Forge

1/2 the fan diameter is a good shroud depth

[Titan151]

Originally Posted by Stang_Man

speculation: fans sitting directly on top of a radiator, sucking air through it, performs better than using a shroud in which the fans are elevated above.

So what I was trying to say is that a fan installed closer to the radiator will not provide any more airflow then one further away. (Installed in a shroud) By elevating the fan you eliminate the dead zone and pull the air through the radiator surface that was once covered by it. Different people have different opinions as to the proper elevation height.

As for smoke testing, this is something that can be benificial as I have used it for wind tunnel testing 1/10th scale model vehicles. But I am not in school any more and the information I obtained in aerodynamics 400 whatever is a little rusty.

Oh and thanks for the info Bill, it will make a great sig!!!

[BillA]

glad to be of help, your sig now is consistant with the post

[AntiBling]

[quote=Titan151]So what I was trying to say is that a fan installed closer to the radiator will not provide any more airflow then one further away. (Installed in a shroud)

Wrong. The farther away from the radiator the fan is, the more air it has to pull to move air through the rad. A fan installed closer to the radiator will pull more air, up to a point. ( 1/2 diameter maybe? LOL ) I dont know at what point that is. However the longer the duct, shroud, pipe, etc, the less the flow will be, assuming the fan doesnt change. You're just physically having to move more air, + frictional losses.