Good to know. Thanks.
Why did you start rebreather diving / what do you love about it ?
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Good to know. Thanks.
I started diving with rebreathers (CC pure oxygen, named ARO).
They were popular here in Italy until 1985, being cheaper than OC scuba air systems. Mostly employed in diving schools, as they make a great training about controlling buoyancy and trim. There were no BCD at the time...
I did love the long autonomy (up to 6 hours) and the very low noise, making it easy to go close to fish.
I did hate the depth limitation (10m max).
They were popular here in Italy until 1985, being cheaper than OC scuba air systems. Mostly employed in diving schools, as they make a great training about controlling buoyancy and trim. There were no BCD at the time...
I did love the long autonomy (up to 6 hours) and the very low noise, making it easy to go close to fish.
I did hate the depth limitation (10m max).
Reason I switched; CCR being the most viable option to safely execute deeper wreck dives.
What I love about it; Its efficiency and new found increased operational range
What I didn't really like; That it took years to be able to do the dives I switched to CCR for.
What I love about it; Its efficiency and new found increased operational range
What I didn't really like; That it took years to be able to do the dives I switched to CCR for.
fsardone
Solo Diver
I am not sure .... what the tech people would do but
According to this article Dissolved Oxygen - Environmental Measurement Systems the best we can think of extracting from water are about 14 mg/l of oxygen.
As each reb diver knows we need about 1-3 l/min of oxygen in normal conditions. Let's assume 2 liters min at 1 bar. Using the standard gas equation PV=nRT n=PV/RT and assuming T = 300 K it would give us .00080225 mol/min of oxygen which is about 13 milligrams per minute. So with a flow of 1 litre per minute of water the requirement of oxygen could be fulfilled ... if we assume 100% efficiency of oxygen extraction and in best conditions. We would also need such flow (pump? Batteries?) BUT
The problem is where would we get the nitrogen to fill our lungs? And do we have counterlungs to empty our lungs into or would we vent gas offboard? In such case the requirement would vary dramatically and become rapidly unsustainable:
Let's say we have counterlung so we only vent CO2. In such case diving to 10 meters and assuming 3 liters tidal volume and 5 liters vital capacity, descending to 10 meters (2 bar) would require to extract from water 5 liters of gas at 1 bar which joining the 5 liters already in the lungs (?) would make up the total 5 liters at 2 bar.
according to this site Nitrogen (N) and water the solubility of nitrogen in water is 20 mg/l (this will also vary with depth and temperature but lets keep it simple) therefore to extract 5 liters at one bar once again using the ideal gas state law (we need to remember that 1 mole in normal condition is 22.4 liters so is about one querter to one fifth) we would need about 0.22 moles which is 3.125 grams.
Once again to extract 3.125 grams of nitrogen from water we would need 156 liters of water with 100% efficiency. Pretty much a water jet while descending.
Finally if I vent the gas instead of recycling it, I would need to replenish (at 10 mt) my tidal volume times the pressure; so at 10 mt 6lt/min at 20 mt 9 lt/min and so on so I would need a water jet pumping several hundred liters of water per minute, depending on depth, through the device.
I am not going into He and narcosis
The gills works because they ensure gas exchanges directly between blood and water, there are no lungs to be filled. I do not think I would like to have my blood rerouted through the device ....!
I think it should be marketed as a scooter also!
Just to have fun!
Cheers
Something wrong in your math. One liter of oxygen at 1 bar, 20°C weights approximately 1.314 grams. As we need 2 liters/minute, that is 2.63 grams. Not 13 milligrams...I am not sure .... what the tech people would do but
According to this article Dissolved Oxygen - Environmental Measurement Systems the best we can think of extracting from water are about 14 mg/l of oxygen.
As each reb diver knows we need about 1-3 l/min of oxygen in normal conditions. Let's assume 2 liters min at 1 bar. Using the standard gas equation PV=nRT n=PV/RT and assuming T = 300 K it would give us .00080225 mol/min of oxygen which is about 13 milligrams per minute. So with a flow of 1 litre per minute of water the requirement of oxygen could be fulfilled ... if we assume 100% efficiency of oxygen extraction and in best conditions. We would also need such flow (pump? Batteries?) BUT
The problem is where would we get the nitrogen to fill our lungs? And do we have counterlungs to empty our lungs into or would we vent gas offboard? In such case the requirement would vary dramatically and become rapidly unsustainable:
Let's say we have counterlung so we only vent CO2. In such case diving to 10 meters and assuming 3 liters tidal volume and 5 liters vital capacity, descending to 10 meters (2 bar) would require to extract from water 5 liters of gas at 1 bar which joining the 5 liters already in the lungs (?) would make up the total 5 liters at 2 bar.
according to this site Nitrogen (N) and water the solubility of nitrogen in water is 20 mg/l (this will also vary with depth and temperature but lets keep it simple) therefore to extract 5 liters at one bar once again using the ideal gas state law (we need to remember that 1 mole in normal condition is 22.4 liters so is about one querter to one fifth) we would need about 0.22 moles which is 3.125 grams.
Once again to extract 3.125 grams of nitrogen from water we would need 156 liters of water with 100% efficiency. Pretty much a water jet while descending.
Finally if I vent the gas instead of recycling it, I would need to replenish (at 10 mt) my tidal volume times the pressure; so at 10 mt 6lt/min at 20 mt 9 lt/min and so on so I would need a water jet pumping several hundred liters of water per minute, depending on depth, through the device.
I am not going into He and narcosis
The gills works because they ensure gas exchanges directly between blood and water, there are no lungs to be filled. I do not think I would like to have my blood rerouted through the device ....!
I think it should be marketed as a scooter also!
Just to have fun!
Cheers
For extracting 2.63 grams per minute, you need to process 200 liters of water. Almost unfeasible, and requiring A LOT of energy.
Last point: I suppose that a standard cylinder full or normal compressed air is assumed to be always available (AND TO BE USABLE AS A BAILOUT). The rebreather should just take care of providing the oxygen being used and to remove the CO2 being generated.
broncobowsher
Contributor
Think of this...
Warm blooded ocean creatures (whales, dolphins, seals, etc) still breath air. Takes air to get enough oxygen to make the energy to keep a warm blooded creature alive.
Warm blooded ocean creatures (whales, dolphins, seals, etc) still breath air. Takes air to get enough oxygen to make the energy to keep a warm blooded creature alive.
broncobowsher
Contributor
Coming to a Kickstarter fund raiser near you.
At least this hasn't progressed as far as the Hydroid did. At least so far.
At least this hasn't progressed as far as the Hydroid did. At least so far.
fsardone
Solo Diver
Sorry Angelo you are right.
I was doing it while bored and commuting on the train ....
I missed a 10^3 factor in the number of moles ...
I bought a rebreather because lifting doubles sucks. I've found I like the rebreather most when I can do a week long trimix, wreck diving trip and this is more than enough gas for the week. The 80s are bailout so they've been full for a long time.
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