breathing apparatus that will allow breathing underwater without tanks!

[bradshsi]

'Dissolved air' does not exist: there is not an air molecule. Centrifuging water will create water-gas (H2O) bubbles - which will collapse the moment the pressure returns to ambient (like water vapour cavitations around a ships propeller). This pressure increase back to ambient is required to deliver any gas to the diver, including water vapour (unless it somehow leaves the centrifuge still at low pressure, in which case the delivery system will act like a vacuum cleaner and suck your lungs out).. There are just so many things wrong here I don’t know where to start.

Cheers,
Rohan.

You are confusing dissolved gas and cavitation. They are two entirely different concepts.

While it is true that there is no air molecule (air being composed of mixed gases), a small amount of each of these gases will dissolve in the water. We routinely need to remove these dissolved gases when we test pumping equipment in a closed loop. This done by lowering the pressure in the loop below atmospheric (i.e. a vacuum). The gas then comes out of solution. We measure how well the water has been degassed by measuring it's dissolved oxygen content.

OTOH cavitation is the localized lowering of the water pressure (often at the inlet of centrifugal pump impellers) which causes water vapor bubbles to form and grow. As these flow from a region of low pressure to a zone of higher pressure they implode. If this occurs adjacent to a surface it can result in damage over time.


Now whether the inventors system will work is another matter entirely. It seems like a very complicated, probably unreliable and energy intensive way to provide breathing gas to a diver.

 

[Tassie_Rohan]

You are confusing dissolved gas and cavitation. They are two entirely different concepts.

While it is true that there is no air molecule (air being composed of mixed gases), a small amount of each of these gases will dissolve in the water. We routinely need to remove these dissolved gases when we test pumping equipment in a closed loop. This done by lowering the pressure in the loop below atmospheric (i.e. a vacuum). The gas then comes out of solution. We measure how well the water has been degassed by measuring it's dissolved oxygen content.

OTOH cavitation is the localized lowering of the water pressure (often at the inlet of centrifugal pump impellers) which causes water vapor bubbles to form and grow. As these flow from a region of low pressure to a zone of higher pressure they implode. If this occurs adjacent to a surface it can result in damage over time.

Mate - there’s no confusion: I used cavitation as an example of water vapour bubble formation in a single phase system due to a drop in pressure. This guy is centrifuging seawater: as pressure decreases in the centrifuge and water vapour bubbles form then other dissolved gases will preferentially partition into this water vapour phase. There’s a whole bunch of partition co-efficients that will tell you how much of each chemical species will do so dependant of the given pressure, temp and chemical conditions of vapour and liquid phases.

The key point, as you also point out, is that when the vapour-liquid mix leaves the centrifuge the water vapour bubble, and the exsolved gases it contains, will implode and return to solution due to the pressure increase. I can’t see how you would separate the small amount of exsolved gas from the water vapour and get it out of the centrifuge and into an ambient pressure breathing loop.

Dropping pressure in an existing two phase (air and water) system such as what you do to degass water will push dissolved gasses out of solution – but only for the duration of the pressure drop: and its not the same as centrifuging a one-phase system (seawater) which is what this guy is trying.

In the later case the first bubbles to form will be water vapour, and any dissolved gases will start to exsolve into the water vapour. You won’t get bubbles of nitrox by spinning seawater.

Cheers,
Rohan.

 

[ClayJar]

T_R: You use the centrifuge to lower the pressure, thus creating bubbles. At the same time, the centrifuge separates the dense water from the less dense gases. You have a tap at the place the bubbles will collect, and into this tube the bubbles are "sucked" by a second pump, which increases the pressure to or above ambient.

I don't see what's the problem with this scenario, but then again, it's basically the same principles as a vacuum distillation tower, and my degree's in chemical engineering. This is just a very small version of the concept.

You know, the more I think about it, the more it seems like a rather elegant solution. By using a single centrifuge as both the vacuum pump to lower the pressure and the separator to collect the evolved gases, you'd get two birds with but one compact stone. I still have no comment on the energy requirements, but for equipment requirements, with just the centrifuge/pump and a pump to compress the evolved gases to working pressure, it could theoretically be rather compact. I suppose the gas-retrieval pump might even be run off the same motor as the centrifuge.

 

[scuba243]

No chemist here my degree is in Psychology/Criminal Justice but I found the reading interesting and I say if you guys got together you might just figure this whole thing out. He still didn't explain how you would circumvent NDL...Cheers!!

 

[Bob Vincent]

I can't believe you people don't know about the inventor R. U. Laughin and his really cool
Whatucallit-Boheccky ... that guy is going to make zillions.