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I built a (relatively) portable air-blowing device that purifies room-temperature ambient air (HEPA, carbon filter), and then heats and humidifies it to 37 °C and RH85%. I use the machine to do aerobic exercise indoors on a treadmill/stationary bicycle: conditioning the air prevents airway constriction (common for people with disabilities like asthma, COPD, long COVID etc). I now wonder if I can put the machine on a cargo bicycle which would allow me commute to work (the machine uses about 1.5 kW, and there are 2 kWh batteries available these days).

The air-purification and heating part is easy, but the humidifier part does not seem to be. The humidifier is, essentially, a stainless (316) bucket of water (~10L) with a thermostat (an off-the-shelf item -- a sous-vide oven). The air is blown over the water surface(about 2 sq feet). Is there a passive (or a low-cost active) method to keep the bucket balanced and to keep the water horizontal to within 10 mm over 30x30 cm area, to prevent the water spilling and being blown inside of the breathing mask? I looked into multi-tube Nafion humidifiers from Perma-Pure, but these are not rated for humans (rated for hydrogen fuel cells), and are too costly (many Ks).

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  • $\begingroup$ Gel the water. Sodium polyacrylate should do. (think diapers). $\endgroup$
    – Phil Sweet
    Jun 3 at 2:49
  • $\begingroup$ Might need a hot water loop for heating it. $\endgroup$
    – Phil Sweet
    Jun 3 at 2:51

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Random idear. Use a gel blanket on top of the heated water reservoir. The gel will acquire water from below and transpire it into the air. The water can be heated normally. Sodium polyacrylate is used in food and hygiene products. Basically, you want a lid made of deposable diapers.

A lid made of thick PVA sponge foam might be good enough, and could be tested for $10.

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  • $\begingroup$ I indeed thought about using a gel, glad to hear you mention it, Phil. I run a biotech lab, polyacrylamide/agarose is what we use for gels (not food safe). Wondering if the gel needs to be poured each time I use the machine -- that would get a bit tedious (at present, the machine takes 30 min to heat up). I will also experiment with hydrophilic sponges. I was thinking to use SS or Al sponges (can be sterilized), but these are costly, and not sure if these are hydrophilic enough. "Sealing" at the edges is puzzling, too -- maybe some kind of SS lip. Could use thick filter paper, too. $\endgroup$ Jun 3 at 14:47

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