Yesterday I took delivery of:
a) An Anemometer
b) A decent-quality sound-level meter
c) A digital tachometer
I also have a positive displacement nutating low-pressure-drop flow-rate sensor capable of measuring flow-rates to 0.01LPM accuracy (when coupled with the digital tachometer - 1RPM = 0.01LPM).
I also have a fanless 12v PSU, and with all of the above I intend to construct a fan noise & air-flow testing station.
I'm not so interested in free-air fan noise levels, because it means nothing. Fan noise does get lower when under load/pressure. I'll measure the free-air noise and flow levels, just for purposes of comparison/validation sake.
What I'm really interested in is air-flow for noise, when mounted on a radiator. Also will be measuring fan RPM where possible (using the digital tachometer again).
Will also compare shrouded, unshrouded, suck, and blow air-flows.
Was just messing with the equipment a bit last night, putting a Yate-Loon on a PA120.1 radiator with a shroud, in suck or blow arrangement. I was able to position the anemometer on the other side of the radiator to get an idea of the evenness of the air-flow through the radiator. Used the tachometer to measure the fan speeds, and the noise meter the fan noise levels. I haven't calibrated the fan noise levels yet to any base reference point, so I won't report the absolute values I got, just the relative values.
Free-air: +0dBA noise, 1480rpm speed
Shroud Suck: -2.7dBA noise (i.e. quieter), 1350rpm speed
Shroud Blow: -3.0dBA noise (i.e. quieter), 1460rpm speed
I found the noise level differences, and the fan speed differences to be quite intriguing. If the fan is spinning faster, it's pushing more air-flow in the blow-mode.
However, using the anemometer on the other side found that with the shroud, in blow mode, the air coming out the edges of the radiator had about an 80% higher velocity that the air coming out the dead-center. In suck mode, the overall air-velocity appeared lower (will need to measure properly later on full-testbed), but it was more even, with only about a 25% variation between the edges (higher) and the dead-center (lower).
So yeah - this throws a cloud over the general suck/blow debate. The fan appears to like to blow much better than to suck, but the air-flow is less even, even though it's of a higher velocity. The fan is also quieter in blow-mode.
It would appear (without further testing) that putting a fan into blow-mode on a radiator with a really deep shroud (60cm) to straighten out the air-flow would be the best way to go, but that's not terribly practical.
It will be interesing to run some tests with varying shroud depths to determine what gives us the best approximation at an even air-flow through a radiator in blow-mode. The current shroud I'm using is a custom job that I made up, that's 6cm deep. I suspect that differing fan shroud depths may favor suck/blow in different amounts.
I then want to apply the guidelines gathered as a result of these tests to measuring actual radiator performance, NOT JUST airflow vs noise, but actual cooling performance with a 200W heat-load. Given that different fans will have different air-spread characteristics, and so create different air-flow speeds through different regions of the radiator, I don't think it's going to be as cut and dried as a "dry run" test of noise vs air-flow. It's going to be noise when mounted vs air-flow vs air-flow characteristics.
This is going to be a long-term effort. I've probably got around 3-4 months to do all this in before my body heals enough to the point that motorbikes and good weather will start distracting me again. So let's see what I can do in that time.
No promises, but that's what's on the cards.
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Originally Posted by Spaceballs
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