To establish the efficiency of a commercially available 80mm to 120mm fan adaptor.
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>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.
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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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
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
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.