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120mm to 80mm Fan Adaptor Study.

Last response: in Overclocking
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<b>AIM:</b>
To establish the efficiency of a commercially available 80mm to 120mm fan adaptor.

<b>METHOD:</b>
a. Measure fan hub and fan blade diameter, and calculate area that the fan blades cover. (in square feet)
b. Measure average fan airflow (in feet per minute) by holding the aerometer to face of fan.
c. Multiply area by airflow to get CFM.
d. Attach 80mm to 120mm adaptor.
e. Measure average airflow again and multiply by the area of the adaptor hole.
f. calculate adaptor efficiency.

<b>MATERIALS:</b>
1 x 80mm to 120mm fan adaptor, <A HREF="http://www.pccasegear.com/category72_1.htm" target="_new">Link, 3rd Pic Down.</A>
1 x Panaflo low speed 120mm fan ~1700rpm<A HREF="http://www.pccasegear.com/prod18.htm" target="_new">Link.</A>
1 x Evercool medium speed 120mm fan ~2200rpm<A HREF="http://www.pccasegear.com/prod564.htm" target="_new">Link.</A>
1 x DickSmith Electronics Air Speed Temp Meter Q1301. <A HREF="http://shop.store.yahoo.com/dse-au/q1301.html" target="_new">Link.</A>

<b>RESULTS:</b>
<b>A. Panaflo</b>
Free flow = 65.5 CFM
Adaptor flow (outer edge) = 38.4 CFM
Adaptor flow (inner zone) = 10.5 CFM

<b>B. Evercool</b>
Free flow = 89.4 CFM
Adaptor flow (outer edge) = 43.2 CFM
Adaptor flow (inner zone) = 14.7 CFM

<b>CONCLUSION & DISCUSSION</b>
Even without doing the Percentage airflow loss one can see that this particular adaptor design is very Inefficient.
And most other adaptors are of similar design.
The shape of the adaptor is all wrong.
Its far too shallow, being only 1" high, undoubtedly cauzing great turbulence and loss of airflow.
Whats worse i found was that airflow accross the face of the adaptor was far from equal, as shown with the outer edge and inner zone airflow rates... the middle of the adaptor hole airlow dropped off remarkably, due to the design and proximity of the fan hub, making it impracticle to give an average % airflow loss.


One thing i did notice was that there was slightly less ariflow loss with the slower fan, possibly as the backpressures involved were less.

<b>THE END</b>

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More about : 120mm 80mm fan adaptor study

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Nice to see actual numbers on this, thanks!

I personally like to use fan grills to attach larger fans to smaller heatsinks, I have gotten good results from that in the past.

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that's a good idea

PooBaa - what were the RPMs of those fans when their CFM was significantly decreased?
i'm wondering if the fans were just slowed or if air was sort of coming out and going in the top, cycling around or something instead of going down through the hole

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Im not sure of the actual rpm with the adaptor fitted, cauz they were running off a molex connector, not a mobo one.

But the fans did change pitch considerably and there was significant air comming back up ... between the end of the fanblades and the fan rim.

At some point i will endevour to find and buy one of those IR/optical fan speed monitoring probes... as well as a cheap sound level meter dunno where to get them though. any ideas?

someday i hope to have a full fan testing kit :) 

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The aluminum 60/80 design, in the first link to the adapters, looks like a lot more efficient design, its ashame it doesn't come in any other sizes.

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indeed, sloped rather than curved. unfortunately heatsink height and case width has a part to play in all this too.

Ive thought about this, and ideally the most optimal 80mm to 120mm adaptor would be 4" or greater higher, gently curving from wide to narrow, with a aerodynamic cone over fan hub.

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yeah, but 4 inches (approx 10cm) is too much to ask for, which is why i think we haven't seen anything like that
2 inches is probably the max that people would buy
2 inches puts the vertical distance (5cm) and horizontal (4cm, from 120mm to 80mm) distance about the same, giving about a 45 degree angle, even a little better. that's probably the best you could hope for

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I was actually thinking of using a case fan attached to the side of the case with a paper funnel sending it directly onto the heatsink. That would likely give me 4 inches, and I've even already got a 120 mm precut hole in exactly the right position. Unfortunately I don't have an aerometer, so I can't do any scientific study like yours.

I've seen cheep decibel meters at Radio Shack, but I haven't been able to find a cheep one which will go below 20 dba.

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oops... just realised i did a fundamental mistake in quoting CFM figures for the inside and middle of the fan adaptor. as they are CFM figures they have been calculate das CFM for the entire hole, so for the edge and middle i should only state air velocities. Actual CFM will be some average of inside and outside multiplied by the hole area.

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