Electronics > Projects, Designs, and Technical Stuff
COVID-19 Emergency - Using UV Lamps to sanitize Face Masks overnight
NiHaoMike:
Found this study linked in the comments:
https://www.ara.com/sites/default/files/MitigateShortageofRespiratoryProtectionDevices_2.pdf
--- Quote from: Mechatrommer on March 28, 2020, 09:04:44 am ---have you done that? looks like you experienced. i did it and yes the old filament stock i tried to dry sagged quite badly but not it become unusable (setting is something like 100degC iirc). the next roll i dried i reduced setting to 60degC and it works. filament brittleness gone and become usable again. for things like paper, tissue, mask etc... i dont think they will combust at 100degC, even if overshooted to say like 150degC.
--- End quote ---
Results vary dramatically depending on the oven, based on what I have read in 3D printing groups. Some suggestions to improve chances of success include letting the oven cycle off before putting in filament and some even suggested turning the oven off but leaving the light on.
I personally keep filament dry by putting it in a bag (mostly sealed but not completely) and leaving it behind my PC.
--- Quote from: Zero999 on March 28, 2020, 10:24:06 am ---I was talking about newer UVC LED-based germicidal lamps. The ones I linked to looked very cheap. I also question their efficiency. The data sheets for UVC LEDs I've found have an efficiency of around 2%, which is miserable compared to the 30% offered by traditional mercury lamps.
http://www.farnell.com/datasheets/2774752.pdf
https://www.ushio.com/files/specifications/germicidal-low-pressure-mercury-arc.pdf
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I think those LEDs are best used for small devices like self cleaning toothbrushes. They're also RoHS compliant although I recall lamps not for general illumination purposes are exempt since many such specialty lamps (UVC being one) have no feasible RoHS compliant alternative.
Zero999:
--- Quote from: NiHaoMike on March 28, 2020, 03:58:11 pm ---I think those LEDs are best used for small devices like self cleaning toothbrushes. They're also RoHS compliant although I recall lamps not for general illumination purposes are exempt since many such specialty lamps (UVC being one) have no feasible RoHS compliant alternative.
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I don't see why UVC LEDs would be better for small devices. 3W E17 lamps are widely available and it should be possible to make small mercury lamps the size of tiny neon indicator lamps, just by changing the gas fill and using quartz for the bulb. The amount of mercury used is tiny. I remember people being concerned about the environmental damage from mercury from compact fluorescents lamps, but it was later found out that the amount of mercury emitted from the extra coal burned to power incandescent lamps, exceeded that by many times.
I can see some advantages of UVC LEDs, over mercury lamps, such as not requiring a warm up time, more mechanically robust, longer life and an unlimited number of on/off cycles, but efficiency doesn't seem to be one of them.
X.G.:
I had used an oven to be a face mask restorer .
http://www.crystalradio.cn/forum.php?mod=viewthread&tid=1838490&extra=
Siwastaja:
I did look at some papers on this, and one advantage identified for the LEDs is that they seem to sanitize better per mW of output, compared to the 254nm mercury vapor bulbs. The reason is likely that the most effective sanitization wavelength range appears to be somewhere around 270-280nm, and 254nm is outside the optimum area, so the LEDs emitting at 275 or 285nm are a better match. Some numbers I remember seeing suggest a difference of maybe 2-3 times, so the final efficiency is still worse than the mercury vapor lamps, but not very much. Is 30% a realistic efficiency number for classical germicidal lamps? I remember seeing lower numbers. OTOH, with no heat-up time, any application requiring intermittent operation (like water or air filtration based on flow rate) benefits from the LEDs.
Looking at the rate of UVC LED development, efficiency and price, maybe they break through in the next 5-10 years. It's likely this crisis puts extra funding on the UVC LED development.
I found quite different requirements for the energy of killing viruses on surfaces with UVC. One study suggested 9J/m^2 or 14 J/m^2 for killing 90%, or 98% of the viruses, respectively. The latter being 1.4 mJ/cm^2, those pesky 10-20mW UVC LEDs might be appropriate for disinfecting more than just toothbrushes. They are still quite expensive, though; one 10mW LED clearly isn't enough to disinfect large area of surfaces or large volumes of air. But I guess there is a lot of difference based on how much material there is for the light to penetrate; for masks, it's useless, as discussed, because the UVC light would need to penetrate many millimeters of the material. A lot of energy is needed for this, likely damaging the material. Heat works better.
I'm personally looking at using UVC LEDs in disinfecting air after proper HEPA filtration. In this use case, there are no large particles that "shade" the UVC light and protect the viruses from the light.
KaneTW:
Germicidal efficiency of UVC leds at optimum wavelengths is maybe 30% more effective than 254nm. Efficiency is still an order of magnitude worse.
The requirements vary and also are not super easy to calculate, but you want a 254nm dose of ~130mJ/cm2 to reach the target for a 99.99% inactivation of even resistant virii. Standards require 40mJ/cm2.
Specifically, this is not the power emitted from the bulb, but actually reaching the microorganism. This isn't a huge issue when disinfecting air, but gets more complicated when disinfecting water.
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