Radiator Backpressure

[Discordia]

Hi everyone, I've been lurking on the forums for awhile, this is my first post - so please bear with me :p:

Background
I'm planning on pulling together a WC loop in the next 6 months or so. I've got a good idea what parts I want, except for fans for my PA120.3 rad.

The Question
What does the back-pressure (relating to airflow) vs airflow curve of a PA120.3 look like? I assume if I know that, I can see approx what CFM the fans will actually push (I'm going for a push config I think) by looking at their pressure vs airflow curve. Eg:

XinRulian RDH1225S
http://img73.imageshack.us/img73/1868/performancecurveegpw2.jpg (http://imageshack.us)


- Discordia

[creidiki]

why push?

just curious, pull's better, especially if you dont plan to run @ full volts.

[J-Mag]

why push?


Don't you think push is better if pull doesn't have a good seal on the rad?

[creidiki]

I'd think they be both just as bed if you havent got a good seal tbh.

Mind you, bad seal imo is not something you work around, but something you fix.

[septim]

you'll need a good seal/well fitting shroud to make push work, otherwise your air pressure just scatters, and i think that air flow does not reach a few centimeters of space between fans.

[Discordia]

Thanks for the replies so far!

I was guided by clokker's (http://xtremesystems.org/forums/showpost.php?p=1504804&postcount=3) Stacker (my case) with his fan's in (I think) a push config in the bottom of his case. If I wanted pull, in the bottom of a case, I'd either have to pull air out of the case (fans below rad) or mount the fans above (in that case how big should the holes in the bottom of my purty case be?). I was uncertain, so stuck with pushing cool air from below...

Any suggestions welcome! :D

But has anyone got the back pressure numbers?

- D

[creidiki]

pull with shroud is the way forward if you want top performance... I have 140mm Yates in pull + 120.3 in the front of my stacker...

[OCme]

pull the cool air from the outside of your case across the radiator FTW...

[septim]

depending on how much floor area you want to cut away...

i would assume about 2 10.5 to 11cm diameter holes...
then the outer 4 screw holes for your fan grill or mesh filter screen...

[Discordia]

I assume you base your support for a pull config on empirical knowledge. Is there also theoretical backing?

Is pull the best specifically for a PA120.3 or rads in general? I'd think direction of airflow isn't a factor (since a radiator core is symmetric). Performance must depend on the fans' characteristics (i.e a Yate Loon is best in pull because of it's unique airflow profile). Say you place a fan far enough away from a rad (with perfectly sealed shroud), would push or pull make any difference? Specifically, does a fan generate higher absolute pressure on one of its' sides? I'd think it's be symmetric.

- Discordia

[OCme]

I assume you base your support for a pull config on empirical knowledge. Is there also theoretical backing?

Is pull the best specifically for a PA120.3 or rads in general? I'd think direction of airflow isn't a factor (since a radiator core is symmetric). Performance must depend on the fans' characteristics (i.e a Yate Loon is best in pull because of it's unique airflow profile). Say you place a fan far enough away from a rad (with perfectly sealed shroud), would push or pull make any difference? Specifically, does a fan generate higher absolute pressure on one of its' sides? I'd think it's be symmetric.

- Discordia

Yes, pulling the cool air across the radiator is known as being the best method for all radiators, and not just the PA120.3. You can use a push/pull fan configuration with 6 fans, 3 on each side of the radiator, but the PA120.3 radiator is so efficient that their would be no gain in performance unless you were using pelts. Yate Loon fans are not any better than any other 12v fan. Yate Loon fans are however special in that they offer unmatched performance for the 27db that they produce & can be undervolted for dead scilent operation.

[creidiki]

I assume you base your support for a pull config on empirical knowledge. Is there also theoretical backing?

Is pull the best specifically for a PA120.3 or rads in general? I'd think direction of airflow isn't a factor (since a radiator core is symmetric). Performance must depend on the fans' characteristics (i.e a Yate Loon is best in pull because of it's unique airflow profile). Say you place a fan far enough away from a rad (with perfectly sealed shroud), would push or pull make any difference? Specifically, does a fan generate higher absolute pressure on one of its' sides? I'd think it's be symmetric.

- Discordia
I've got a few ideas as to why its happening, but none thats easily verifiable.

When Radical_53 started his tests we threw around a few ideas.

Heres a thing though: its not deadspot, because it happends even with shrouds. With YL D12SL-12s @ 4v, pull has like a 3k advantage over push on a PA120.3, when both are with shrouds.

It cant be pressure differentials because if you think about it, you have the same pressure differential across the fan in both configs.

The only thing I can think of that the chopped up air coming out of the fans doesent cool as well as a quasi-laminar stream.

This would go against what the majority of people think, but people make an error of applying the rules about water to air... the viscosity is very different. Unlike water, skin effect with air is very subtle effect.

[Discordia]

That makes sense. Thanks OCme & creidiki! Me want quasi-laminar stream!

Any idea where I can see Yate Loon pressure/air flow data?

[creidiki]

I think Petra has the curves. Or at least, he asked YL for them. Dunno if they ever actually sent them to him.