Making electricity with scuba regulator, has it been done?

[KenE]

The energy calculations seem reasonable, but you must reduce to account for the energy needed/consumed by the first stage and second stage regulators. I believe this reduction will reduce the amount of available energy for electricity will mirror a single battery cell. As mentioned above, adding anything in the stream from tank to lungs is a risk not acceptable to most divers.

 

[Angelo Farina]

There is another factor to consider: temperature.
When air is laminated in the valves of first and second stage, the enthalpy of the compressed gas is substantially preserved. As air is quite close to a perfect gas, ans isoenthalpic expansion results into an isothermal process.
So the temperature of the gas does not drop significantly, just a few degrees due to the Joule-Thompson effect (caused by the fact that air is not exactly a perfect gas).
But if, during the expansion, you convert part of the initial enthalpy to mechanical work, instead of dissipating it into heat in the lamination process, at the end of the expansion the remaining enthalpy of the gas will be much smaller than the enthalpy at the beginning. And hence also its absolute temperature will be reduced significantly, dropping way below the freezing point. This causes a lot of problems, the regulator can easily be locked in free flow by the ice.
For cold water diving, regulators are usually designed for getting a pressure reductoin almost isothermally.
Converting this to an almost adiabatic expansion is truly a bad idea, as the resulting gas absolute temperature can easily become half of the original one, if half of the available energy is converted to electrical energy.
So if we start at 300 K (27 °C), the temperature will drop to 150 K (-123 °C) causing everything to freeze, and making the gas not breathable.

 

[Subcooled]

Something I have thought about over the years is how to use the energy in a full dive tank to make power,
That can be used for dive light or heat your suit, some small load,]

Two sources:
1) mass flow > electricity
2) pressure drop > cooling effect

 

[Subcooled]

There is another factor to consider: temperature.
When air is laminated in the valves of first and second stage, the enthalpy of the compressed gas is substantially preserved. As air is quite close to a perfect gas, ans isoenthalpic expansion results into an isothermal process.
So the temperature of the gas does not drop significantly, just a few degrees due to the Joule-Thompson effect (caused by the fact that air is not exactly a perfect gas).
But if, during the expansion, you convert part of the initial enthalpy to mechanical work, instead of dissipating it into heat in the lamination process, at the end of the expansion the remaining enthalpy of the gas will be much smaller than the enthalpy at the beginning. And hence also its absolute temperature will be reduced significantly, dropping way below the freezing point. This causes a lot of problems, the regulator can easily be locked in free flow by the ice.
For cold water diving, regulators are usually designed for getting a pressure reductoin almost isothermally.
Converting this to an almost adiabatic expansion is truly a bad idea, as the resulting gas absolute temperature can easily become half of the original one, if half of the available energy is converted to electrical energy.
So if we start at 300 K (27 °C), the temperature will drop to 150 K (-123 °C) causing everything to freeze, and making the gas not breathable.

I'm pretty sure I've seen the definition of enthalpy, and done some basic calculations, but I've forgotten that stuff.
I fear very few people understand enthalpy. Could you explain it in plain terms?

 

[Gone for diving]

I my though was that
cold is the energy, removed and dissipated into the water from the compressed air, at the first stage pressure drop.

Spinning a turbine or something like that would remove some of the cold energy, and improve the outlet temp and make it warmer...

(Pushing oil through an orfice, creates heat, I assume the air would be similar) (or maybe it acts like refrigerant) just didn't think it will make thing even colder....

I would say the turbine should be in the highest pressure differential.
A type of first stage will be needed, but if there was a controlled leak, into a 150psi over ambient storage buffer tank, that the second stage hose came off of, the first stage valve would not need to close completely unless the person stopped using the reg,

 

[Angelo Farina]

I'm pretty sure I've seen the definition of enthalpy, and done some basic calculations, but I've forgotten that stuff.
I fear very few people understand enthalpy. Could you explain it in plain terms?

Enthalpy is simply M×cp×T.
cp is the thermal specific capacity of a gas at constant pressure. This is the amount of heat required for increasing by 1 K the temperature of 1 kg of gas.
For air at normal temperature and pressure cp= 1 kJ/(kg×K).
So a mass M of 3 kg of air at T= 300 K has an enthalpy of 900 kJ.
You can think at it as the total energy available.
The enthalpy does not depend on pressure if the gas is a perfect one...
But pressure is what allows the gas to expand, releasing its enthalpy and dropping its temperature.
If the expansion is not producing work, the enthalpy remains constant, and also temperature does not drop.
All this is not truly exact, as air is not exactly a perfect gas.

 

[Angelo Farina]

I my though was that
cold is the energy, removed and dissipated into the water from the compressed air, at the first stage pressure drop.

Spinning a turbine or something like that would remove some of the cold energy, and improve the outlet temp and make it warmer...

(Pushing oil through an orfice, creates heat, I assume the air would be similar) (or maybe it acts like refrigerant) just didn't think it will make thing even colder....

I would say the turbine should be in the highest pressure differential.
A type of first stage will be needed, but if there was a controlled leak, into a 150psi over ambient storage buffer tank, that the second stage hose came off of, the first stage valve would not need to close completely unless the person stopped using the reg,

Sorry, but all these concepts are substantially wrong...
It would need a couple of chapters of a good book on thermodynamics and thermal machines for explaining everything properly.

 

[Subcooled]

Enthalpy is simply cp×T.
cp is the thermal specific capacity of a gas at constant pressure. This is the amount of heat required for increasing by 1 K the temperature of 1 kg of gas.
For air at normal temperature and pressure cp= 1 kJ/(kg×K).
So a mass of 3 kg of air at 300 K has an enthalpy of 900 kJ.
You can think at it as the total energy available.
The enthalpy does not depend on pressure if the gas is a perfect one...
But pressure is what allows the gas to expand, releasing its enthalpy and dropping its temperature.
If the expansion is not producing work, the enthalpy remains constant, and also temperature does not drop.
All this is not truly exact, as air is not exactly a perfect gas.

So, in terms of the kinetic gas theory,
enthalpy is a measure of the (kinetic) energy of all the gas atoms/molecules together?
So, it tells what the absolute maximum amount of work is that a certain amount of (heated?) gas can do?
Oh, you already said "the total energy available"... So probably yes.

Aren't pressure and temperature about the same thing? Molecules hitting the walls? One measures the amount of collisions (amount of stuff) times speed, ie. pressure, the other measures speed only (temp).

 

[Gone for diving]

I am sure I am, not the first one to think of this.... so that explains why its probably not been done,

Reading your first post about 6 times,
Its starting to make some sense,

Being a mechanic and working on some AC systems, I have some basic knowledge of how this work,

Can you explain in basic terms then,
Where all the bulk of the energy in the dive tank goes, as you breathe it,?
Sure some is moving valve's, noise etc,
temp is the big one, from what I understood...

 

[DiveHewi]

Hey OP! I like the way you think!
I think outside of the box myself from time to time. Now, If we can just manage to stay alive for a little while longer, maybe we'll come up with something!