3 ms·

Well now I guess I have to do the math: W = P(b)V(b) ln(P(a)/P(b)) (https://en.wikipedia.org/wiki/Compressed_air_energy_storage https://en.wikipedia.org/wiki/

by Alkim 11y ago

Well now I guess I have to do the math: W = P(b)V(b) ln(P(a)/P(b)) (https://en.wikipedia.org/wiki/Compressed_air_energy_storage https://en.wikipedia.org/wiki/Compressed_air_energy_storage) CPAP requires roughly 10 cm of water pressure = 0.01 Bar Sea level atmospheric pressure is roughly 1 bar So the device has to pressurize to 1.01 Bar Now I’ve looked it up, and a typical CPAP machine moves 20 to 60 liters per minute Let’s say 30 liters per minute = 1800 liters per hour W = (1.007)(1.8)ln(1/1.007) = (1.81)*(-00698) = 0.0127 MJ = 3.53 Watt Hour So assuming perfect efficiency you would still need 28.64 watt hours of battery, just to do the compression. 470 Wh/kg for Zinc-air battery implies this device requires a 60gm battery (2 oz to those of us of a certain age) I looked up CPU fan efficiency (what they say they derived it from) and PEAK fan efficiency only approaches 25% http://www.nmbtc.com/fans/white-papers/fan_efficiency_important_selection_criteria/ http://www.nmbtc.com/fans/white-papers/fan_efficiency_import... So, you’d really need an 8 oz battery hanging from your nose to make this work, not counting what you need to run the electronics, etc.

amluto 11y ago
Where does that 30 liters per minute go? I'm reasonably sure it's not going into the user's nose or mouth. Part of the claimed innovation here is that the thing sticks directly into the user's nose. If it seals well, it's plausible that there's very little wasted air, which would account for the factor of roughly five. (Also, you used the formula for isothermal compression, I think. A tiny little device like they showed would probably move air quickly enough through its fan that it would be closer to adiabatic. This doesn't matter much for the small pressure change involved.)
- dragonwriter 11y ago
  > Part of the claimed innovation here is that the thing sticks directly into the user's nose. Putting the whole machine in the nose is novel, but I don't see how that is innovative in terms of changing required functionality compared to nose-only masks, which are already a thing.
  - amluto 11y ago
    It shouldn't have anything to do with the required technology. It might allow a considerable reduction in leakage, though.

by Alkim 11y ago

amluto 11y ago

Where does that 30 liters per minute go? I'm reasonably sure it's not going into the user's nose or mouth. Part of the claimed innovation here is that the thing sticks directly into the user's nose. If it seals well, it's plausible that there's very little wasted air, which would account for the factor of roughly five. (Also, you used the formula for isothermal compression, I think. A tiny little device like they showed would probably move air quickly enough through its fan that it would be closer to adiabatic. This doesn't matter much for the small pressure change involved.)

dragonwriter 11y ago
> Part of the claimed innovation here is that the thing sticks directly into the user's nose. Putting the whole machine in the nose is novel, but I don't see how that is innovative in terms of changing required functionality compared to nose-only masks, which are already a thing.
- amluto 11y ago
  It shouldn't have anything to do with the required technology. It might allow a considerable reduction in leakage, though.