PA160 with 2x92mm and custom shroud?
 

Hi,

In my endless speculations of the perfect radiator for my case I now ask how it would be to mount 2x92mm fans on a Thermochill PA160 by a custom shroud?

I know PA160 is "made" to perform with a 120mm fan, but 1x120mm lownoise against 2x92mm lownoise the 92's will move more air through the radiator. 2x92mm will also fit my case better (since they fit between a 3,5" wich I have to partly move/modify to fit the PA160. Can't remove it entirely since it will make the case construction unstable).

My only fear is that because of PA160 is a single pass radiator uncooled water will pass. The radiator is 165mm wide and the fans only 92mm - 36mm "uncovered" fins to each side of the fans and it would proberly take "a lot" under pressure in the shroud to make it suck decently in the wide placed fins.
Anyone have a opinion on this?
A PA160 is priced 120$ without shroud so I'm not just gonna buy it and try.

I attached a picture of how I had in mind to place the fans (the fan size fits the ratio)

Re: PA160 with 2x92mm and custom shroud?
 

The pressure rating of the fan (ie. how many CFM's at what pressure) not the fan size, determines how much air it will push in any given system. It is very po9ssible that the 120 mm fan will push more air through than will 2x92's. You have to look at the fan's specs to know.

If you are going to use the 2x92's why not make a shroud that covers the whole face of the rad?

Re: PA160 with 2x92mm and custom shroud?
 

Ahh, I had in mind to make a shroud that covers the whole radiator except for the barbs (fans sucking) and with a air-sealing between the shroud and radiator. I just didn't draw the shroud on the picture - only the size of the 92mm fans. I see now that I made the picture "confusing".

The fans are 92mm Enermax UC-9FAB - rated 1500-2500RPM and 28-47CFM. I found out that 1800-1900RPM are at the level of noise I can tolerate so calculating the airflow at 1800RPM it will be blowing 33,84CFM - a total of 67,68CFM with 2 of them. That's more than one 120mm @ 1300RPM can blow (~44CFM).
Enermax have a speciel RPM regulation (patented?) method that regulates the fans inner resistance so it's allways 12v. It should give a variable fan that allways have the best terms of overcoming air-resistance.

But my biggest concern is that the airflow through the radiator won't be balanced with 2x92mm fans since the radiator is so much wider than the fans. I think it will suck most air through the center of the radiator meaning that water passing through in the outer channels won't be cooled good enough.

Could a custom shroud with same design guideline as the original 120mm shroud (40% of the fan size from the radiator core) make the airflow about even through all of the fins?

Re: PA160 with 2x92mm and custom shroud?
 

That's figures in open air, not against a backpressure. The rad will create a static pressure that makes the flow drop. The pressure/flow relation is not linear, so without at least mfger data about the fans you're about to use, you won't get any idea. Also you'll certainly have a drop in performance/noise ratio, as 92mm fans make quite more noise to push as much air as a 120mm.
If you want a powerful & quiet 120mm try the Delta WFB1212M, i've been impressed by this one, it's up there with the best of them if you want quietness, and it flows 72 CFM at 2100rpm...
Overcoming "air resistance" is more a factor of the blades geometry, and total surface. Most (if not all) fan motors have quite enough power to rotate at their full rated speed whatever the conditions are.

With proper ducting (large enough shroud) this is not really an issue.
Keep the 120mm shroud, ans slap a 120mm fan on it.

Re: PA160 with 2x92mm and custom shroud?
 

How do I find this data? isn't this specification only public with industry targeted fans like Delta, Papst and Panaflo?

The fan is Enermax UC-9FAB.

120mm @ 2100RPM is definately not quiet in my ears. A Papst 120mm running 1600RPM (55CFM) is driving me insane. I have the Papst 120mm fans and the two Enermax 92mm and the two Enermax 92mm running at 1800RPM is tolerable and moves more air than my Papst 120mm - even with the Papst full speed.

I don't know the proper word in English to describe what I mean. If you have a Papst 120mm at 12v and stop the fan with a finger, then when you remove it the fan will immidiately spin to full speed. Having the Papst on 5v og 7v it can barely start again after this action. In my experience it looses power that affects the performance when mounted on a radiator - don't know why, but I guess it's because of lowered (back?)pressure wich results in worse heattransfer from copper to air.
At that point the Enermax have "full throttle" at all RPM speeds in the variable area.

Any idea of how big? 92 x 40% = ~36,8mm from the radiator core?

Re: PA160 with 2x92mm and custom shroud?
 

It's because the motor of the PAPST doesn't have enough torque to overcome the polar magnets when it's run much below 7v. Nothing to do with backpressure etc, just not enough power for the motor to overcome magnetic force. Bigger blade requires more torque to move it from pole to pole. Better to find the correct 120mm fan.... which the PAPST obviously isn't for your purposes.

Re: PA160 with 2x92mm and custom shroud?
 

For those 3 the data is on their site (in the PDF specs). They make excellent fans IMHO so no need to look further. The problem is, how much backpressure a given rad/shroud combo creates ? It's being solved here in these forums...

It's an average fan: produces average flow, average noise, at least according to data i've seen until now. There are certainly 120mm fans that produce the same flow for less noise, or more flow for the same noise. Think car engine: there's no replacement for displacement :P

Did you try this particular fan ? The blades shape incur different noises, each mfger choose different approaches. The tip vortex is responsible for most of the noise in some cases, and in other cases it's the engine itself. Try this Delta fan, i've got an ADDA reference as well that's very good (the ones sold with Lian Li V-Series cases)

Which model is it. The Papst 4412 N/2GL i have is one of the most silent i know at 12V. It doesnt support undervolting though, the engine starts to hum.

For the next point Marci answered it very well. It's a problem of engine torque, not air backpressure. There are *real* variofans made by Papst but unfortunately they're not the most quiet.


I believe someone published a rule of thumb here on these forums at one point, i can't remember the exact figure though. IIRC it's closer to 33% (1/3) but what i recall as well is it's better to have too large a shroud than too narrow.

Re: PA160 with 2x92mm and custom shroud?
 

Incorrct! As others have been pointing out you need data like the attached (for the Papst 4300N series from their website). As to where to get this data, what I do is if the data isn't readily available at the seller's or Mfgr's website, it's good by! You can't intelligently choose a fan without it. The data for rads is much harder to find and sometimes interpolation is reguired...but still, W/O data how can one choose?

Re: PA160 with 2x92mm and custom shroud?
 

The other 120mm fan i was surprised by is the ADDA ref. AD1212LB-A71GL. It's a ball bearing and though it's just as quiet (subjectively) as a sleeve bearing. I am not sure it moves as much air as the Delta though (i didn't check the figures)