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Radiator Airflow vs Static Pressure

4K views 2 replies 3 participants last post by  CrazyElf 
#1 ·
Previously I measured the performance of various fans. I published the results in OCN's Air Cooling forum, here. Unfortunately, I cannot measure the static pressure directly, so I did not cover that aspect of these fans. However, some of the manufacturers stated the static pressure of their fans.

I decided to look at the performance of the fans pushing air through my 30 fpi (fins per inch) Hardware Labs Black Ice GT Stealth radiator vs the nominal static pressure specified by the manufacturer:



Now, the two sets of numbers from the 38mm San Aces and the 25mm "Silent" San Aces seem to form a continuum, so I graphed the results:



Yup. Not only do the two sets of San Aces form a continuum, but the Gentle Typhoons closely overly the San Ace traces.

What is the take-away here? If you trust the static pressure specs of a manufacturer, you can get a relative notion of how well a fan will do on your rad.

Note that I am not including specs from brand sellers or OEM's here. The accuracies of those specs have to be ascertained on a practical model-by model measurement.
 
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#2 ·
Hmmmm.
I took the liberty of "massaging" your data a little bit.
I graphed air flows vs percentage of airflow lost when going through a rad.



Note thatr the lower CFM fans tend to loose a much higher percentage of their nominal air flow when going through a rad.
I wonder if this disproportionate loss is because of basic RPM, Blade Design, Fan design, or something else?
It would be interesting, and perhaps helpful to those under-volting their fans to run your tests again, but at 7 volts.
That may also shed some light on the above question.
 
#3 ·
The really interesting question is their location on the PQ curve.

One method that I have tried is to try to estimate the real world position on the PQ curve and then to take the location then use that.

Quote:
Originally Posted by billbartuska View Post

Hmmmm.
I took the liberty of "massaging" your data a little bit.
I graphed air flows vs percentage of airflow lost when going through a rad.



Note thatr the lower CFM fans tend to loose a much higher percentage of their nominal air flow when going through a rad.
I wonder if this disproportionate loss is because of basic RPM, Blade Design, Fan design, or something else?
It would be interesting, and perhaps helpful to those under-volting their fans to run your tests again, but at 7 volts.
That may also shed some light on the above question.
The reason is because static pressure is the square of the fan rpm. So if I double my fan rpm, then I will have 2^2 or quadruple the static pressure.

Remember fan's laws:

- CFM is proportional to the RPM, so a 2x increase in RPM with lead to a 2x increase in CFM
- Static pressure is to the 2nd degree of RPM, so 2x RPM would mean that you get 2^2 or 4x the static pressure
- Power consumption is a 3rd degree function. A 2x increase in RPM needs 2^3 or an 8x increase in power consumption.

Power consumption goes higher than 2x if you were to have a fan approaching the sound barrier, but that's not relevant for our purposes.

Which fan do you want to see undervolted? I can calculate the approximate values.
 
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