Maximum voltage from blowing through small turbine?

[anorlunda]

Let's do a little back of the envelope calculations.

https://en.wikipedia.org/wiki/Electrolysis_of_water

Efficiency of modern hydrogen generators is measured by power consumed per standard volume of hydrogen (MJ/m3), assuming standard temperature and pressure of the H2. The lower the power used by a generator, the higher would be its efficiency; a 100%-efficient electrolyser would consume 39.4 kilowatt-hours per kilogram (141,840 J/g) of hydrogen,[17] 12,749 joules per litre (12.75 MJ/m3). Practical electrolysis (using a rotating electrolyser at 15 bar pressure) may consume 50kWh/kg, and a further 15kWh if the hydrogen is compressed for use in hydrogen cars

https://en.wikipedia.org/wiki/Respiratory_minute_volume

Minute ventilation during moderate exercise may be between 40 and 60 litres per minute.

So 50 liters of air per minute is 3000 liters per hour, of which 3000*0.21 or 630 liters is oxygen. That is 0.9 kg oxygen/hour, that means you need 50*0.9=45 kw of electric power to supply your own oxygen. And that makes no correction for the pressures needed at scuba depth, nor any correction to capture and recirculate the other 79% of the breathing mixture.

Compare 45,000 watts for a rebreather with 10 watts for cell phone charger, and you see that the energy needs for an electrolysis rebreather are about 4500 times more than what your lungs can produce.

 

[twiz_]

Let's do a little back of the envelope calculations.

https://en.wikipedia.org/wiki/Electrolysis_of_waterhttps://en.wikipedia.org/wiki/Respiratory_minute_volumeSo 50 liters of air per minute is 3000 liters per hour, of which 3000*0.21 or 630 liters is oxygen. That is 0.9 kg oxygen/hour, that means you need 50*0.9=45 kw of electric power to supply your own oxygen. And that makes no correction for the pressures needed at scuba depth, nor any correction to capture and recirculate the other 79% of the breathing mixture.

Compare 45,000 watts for a rebreather with 10 watts for cell phone charger, and you see that the energy needs for an electrolysis rebreather are about 4500 times more than what your lungs can produce.

Thanks for your response. I figured that wouldn't work out as well as I hoped, so I sort of put that to the side. Now I'm curious about making the bike alternator, which I'm hoping will produce a much closer wattage to the one you decribed, and perhaps more after that. Every source I found had something different for oxygen consumption, so I'm also curious as to how much error might be involved, especially on a bike.

I just read that a bike generator typically produces about 100 watts depending on the rider, so that gives me some amount of confidence.

 

[anorlunda]

Now I'm curious about making the bike alternator, which I'm hoping will produce a much closer wattage to the one you decribed

I just read that a bike generator typically produces about 100 watts depending on the rider,

You must have misread. I said it needed 45000 watts, or 450 bike generators.

Edit: someone please double check my calcs in #36. It sounds like I dropped a decimal.

 

[twiz_]

You must have misread. I said it needed 45000 watts, or 450 bike generators.

Edit: someone please double check my calcs in #36. It sounds like I dropped a decimal.

Ah. You said kw, I did misread haha. That's way out there.

 

[russ_watters]

You must have misread. I said it needed 45000 watts, or 450 bike generators.

Edit: someone please double check my calcs in #36. It sounds like I dropped a decimal.

I don't see any missed decimals, but didn't you use the energy per mass of hydrogen produced instead of the mass of oxygen? So I think you need to divide your answer by 4.

 

[anorlunda]

I don't see any missed decimals, but didn't you use the energy per mass of hydrogen produced instead of the mass of oxygen? So I think you need to divide your answer by 4.

Thanks Russ, you're right. 11250 watts, or 15 hp sounds more in the ball park.

Sorry twiz, that's still more than 112 bike generators.

 

[OmCheeto]

Thanks Russ, you're right. 11250 watts, or 15 hp sounds more in the ball park.

Sorry twiz, that's still more than 112 bike generators.

Does that Respiratory_minute_volume thing take into account that the lungs only extract about 25% of the oxygen in the air?

Oxygen Absorption Rate in Lungs | Lung Efficency at Capturing Oxygen
...
During normal breathing, oxygen content in the inhaled air is 20.9%, while in the expired air is 15.3% (see above). Hence, 5.6% of air is extracted or captured as oxygen. This oxygen remains in the lungs and is used by the human body.
...

Even at a rough estimate of 25%, that's still 2800 watts.
And according to wiki

Human Power [wiki]
Available power
A trained cyclist can produce about 400 watts of mechanical power for an hour or more, but adults of good average fitness average between 50 and 150 watts for an hour of vigorous exercise. A healthy well-fed laborer over the course of an 8-hour work shift can sustain an average output of about 75 watts.

that translates to 7 bicyclists, 28 good fitness adults, or 37 laborers, just to supply enough power for 1 person to breath.

I don't think this will work.

I would study fish. They seem to have figured out how to breath underwater.