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> Because they are designed to be quiet and still provide good flow of air they produce almost no pressure differential to speak of and the flow can be halved by a wire mesh that is a bit too dense

There are high static pressure fans which address this problem, specifically designed to work with pressure differential, usually used to blow air through radiators for water cooling. The fan linked in the github page (Noctua NF-F12, the "cheap fan" in the picture) is such a fan, it provides a static pressure of 7.63 mmH2O, which is very high.

Edit: you can get regular-sized 12cm pc fans that need 48 watts and rotate at 7160rpm, move 7.160 m^3/min air at 35.877 mmH2O static pressure:

https://www.frozencpu.com/products/8147/fan-500/Delta_Mega_F...

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> it provides a static pressure of 7.63 mmH2O, which is very high.

Actually, it depends on the specific HEPA filter if that is enough or not. If it's not enough, the air will find the path of less resistance and circulate in and out thru the fan blades, but not thru the filter.

For some HEPA filters you can find specs. These (https://www.airclean.co.uk/download/4724) are spec to 250 Pa which would be about 25 mm H2O if I am correct.

Even if they don't recirculate, I sort of doubt that these small fans are going to achieve sufficient air flow through the filter (a radiator is much less of an obstruction than a HEPA filter).

> it provides a static pressure of 7.63 mmH2O

If anyone else is wondering, that's about 0.8 mbar (roughly 8 ten-thousands of an atmosphere), or 80 Pa of over-pressure.

To put this into perspective, my local atmospheric pressure varied about 2000 Pa in the last 48h due to weather changes.

Lemme go send my air intake through a time machine and as long as the weather keeps changing we can use that to drive air through a filter!

No need for a time machine (or being snarky - I did say it's just for comparison, didn't I? I think it does put the "very high pressure" into perspective)

That said, your time machine idea could be simply implemented with a large, airtight box. Simply put the filter over it and weather changes will push and pull air through the filter with two orders of magnitude more pressure than this little fan. Volume of filtered air will depend on the volume of the box though, so better get a large one.

If you had a time machine you might as well just skip the filter and pull in air from before the industrial revolution directly

IMO, absolute pressure doesn't give much of a perspective.

Car tire pressure is about 1.8-2.5 Bar.

Your 2000 Pa atmospheric pressure change is about 20 mBar.

Pressure in an inflated balloon is about 2 mBar (0.002 Bar).

Noctua's static pressure is 0.8 mBar. Let's call it 0.5 mBar dynamic working pressure.

Not as low as I expected. Not sure if it will have a semi-reasonable speed, but that will definitely push some air.

Another comparison, 0.5 mBar is 50 Pa = 50 N/m². That gives about 50 * 0.3 * 0.3 / 10 ~ 0.5 kg force on a 30x30 cm² surface.

Finally, as the article video and data shows, it does actually work.

[1] http://scipp.ucsc.edu/outreach/balloon/labs/InflationExp.htm

That balloon figure doesn’t make sense to me in relation to atmospheric pressure changes. It would mean that a tied-off balloon would randomly inflate and deflate itself depending on weather.

It does, slightly. Pressure change 20 mBar = 2% of absolute atmospheric pressure -> about 2% balloon volume change, with corresponding 2% internal absolute pressure change, while keeping the same low differential inside-outside pressure.

https://noctua.at/en/nf-f12-pwm/specification

Static pressure 2,61 mm H₂O <-- according to the vendor

I got it from here:

https://noctua.at/en/nf-f12-industrialppc-3000-pwm/specifica...

Or if you just follow the link on the linked page:

https://www.pccasegear.com/products/27866

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