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post #9 of (permalink) Old 08-17-2013, 02:44 AM
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Originally Posted by Jakusonfire View Post

Warning: Spoiler! (Click to show)
Its much like pumps and loop restriction if you are familiar with that.

Any radiator ( or any air obstruction .. filter, fan grill) has a certain restriction to airflow. The denser the FPI and the thicker the inner tubes the higher it is (roughly)

This is equivalent to the pressure drop graphs you see for water blocks etc ... the higher the flow, the more resistance.

Fans have a PQ curve that will trace how much pressure they exert on the air from 0 flow rate all the way up to their maximum flow rate that is only seen with 0 restriction.

Fans marketed as "high static pressure" will usually have a curve that starts high on the left side, indicating high pressure at 0 flow and will dive down quite steeply to their max flow rate and 0 pressure.
Fans with very steep blades will start off relatively low on the pressure at 0 flow but the graph will decrease at a much more shallow rate to end up at a higher flow rate at 0 pressure.

This graph is from the Noiseblocker eloop datasheet.
The yellow curve is very roughly the same yellow curve from the graph above for the Black Ice rad in converted units
The Black dots are roughly the curve for the Scythe GT AP15 from above converted in to the units for this graph.
The straight red line is an imaginary High static pressure fan
The straigh blue line is an imaginary high air flow / low static pressure fan

We can see that the AP 15 and eloop B12-3 (green curve) cross the line of the rad curve at very close to the same point, even though the eloop is rated to some 20 cubic meters an hour higher flow. At full speed both fans would produce about 60 m3/h air flow rate.
The eloop B12-ps (dashed blue line) is rated to the same max flow rate as the AP15 but the higher static pressure of the AP15 means it crosses the rad curve at a much higher flow rate. 50 vs 65ish m3/h air flow.

The imaginary fan lines are just to show how it is possible for fans with very different manufacturer specs to end up being relatively close to the same flow rate through a radiator or grill.

A more restrictive rad will have a steeper restriction curve that will favour fans that stick to the high pressure parts of graphs. Lower restriction rads have a more gently sloping restriction curve and are a little more tolerant of different fan types as their curves will intersect at flow rates that are not too far apart.

Obviously this isn't meant to be a scientific comparison of different fans on rads ... just to outline the concept and how it works, so go easy.
The only reason these two fans were used is that they are both made by the very few companys that actually publish proper data.
The radiator air restriction graph is a very old one too so don't think that it applies exactly to modern rads

Jakusonfire always to the rescue with the extensive explanations complete with graphs and examples.*Golf clap*

Originally Posted by xconwing View Post

Hello fellows Oc,

I've look around for fans to best fit for radiator configuration and they all point to high "static pressure" fan. I don't agree with this but since it's me against a multi-billions dollar company, the doubt are in my part. From what i gathered:

high static pressure (SP): more blades, blades oriented slightly parallel to the fan face, "ideal for rads"
high air flow (AF): fewer blades, blades oriented slightly perpendicular to fan face, "ideal for case"
Warning: Spoiler! (Click to show)
base on the blades angle, the air blown would be illustrated as below:

please excuse my crude drawing
If the picture shown is correct, then air pressure at any point in an AF should be higher (allow air to go around obstruction, like a rad) then the SP fan. Therefore it would make sense that AF should be chosen for rads. Additionally, AF fans have less rpm (equates to less noise) than SP.
Warning: Spoiler! (Click to show)
Data I gathered:


Your assumption that airflow is better for radiators is correct. Simply put, higher airflow means the air doesn't have as much time to heat up, resulting in lower deltaTemperatures. On the other hand higher rated airflow fans will not always actually have more airflow than high SP fans once you introduce notable amounts of restriction. SP fans will usually end up having MORE airflow through radiators because they can handle the restriction better. For more detail on that, let us go back to Jakusonfire's post. biggrin.gif

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