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Author Topic: Can Electrolysis Be Used As a Propulsion Method?  (Read 10165 times)

Offline Bored chemist

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #25 on: 21/02/2013 19:54:02 »
Profound, other members have patiently pointed out to you the practical deficiencies in your imaginative proposal. I hope all would applaud the application of innovative thinking to problems. As you implied yourself it is such thinking that leads to advances in technology and ultimately to quality of life. However, the imagination must be balanced by skepticism and robust critique of any proposal.

Would you agree, in the light of the clearly documented weaknesses in your proposal, that it is not viable as a practical propulsion system?

burning kerosene and oxygen can create a dangerous fire/explosion hazard.it is highly dangerous and can only create thrust for very short time periods.it is highly impractical.
That's demontrably false.
Commercial air travel relies on burning kerosene the engines run for hours at a time and have long lifespans.

Since it's not true, it clearly doesn't support your argument.
Why did you post it?

Also, any news of the "pressures of over 10000 psi are impressive and routinely achieved in industrial chemical electrolysis processes."
or do you accept that it simply isn't true?
Apart from anything else it would be a bit odd. The voltage needed rises with the pressure so it would, for most purposes, be more efficient to run at near atmospheric pressure.

 

Offline CliffordK

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #26 on: 21/02/2013 21:23:24 »
Also, any news of the "pressures of over 10000 psi are impressive and routinely achieved in industrial chemical electrolysis processes."
or do you accept that it simply isn't true?
Apart from anything else it would be a bit odd. The voltage needed rises with the pressure so it would, for most purposes, be more efficient to run at near atmospheric pressure.
Profound did post a link here:
http://www.thenakedscientists.com/forum/index.php?topic=46355.msg404240#msg404240

Although, this appears to point towards a research article, and not necessarily indicating that it is routinely used in industry at this time.  But, their theoretical efficiency of the high pressure electrolysis did indicate that it may in fact be competitive with low pressure electrolysis as far as energy consumption.
 

Offline Bored chemist

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #27 on: 23/02/2013 12:48:37 »
He posted a link in response to my challenging his assertion that "pressures of over 10000 psi are impressive and routinely achieved in industrial chemical electrolysis processes."
But, since they are not using pressures above 10,000 PSI ad they are not an industrial process, they don't actually support his claim.
That's why I asked him if he had " any news" of the "pressures of over 10000 psi are impressive and routinely achieved in industrial chemical electrolysis processes."

It seems he hasn't- or , at least, he hasn't cited any.

It remains the case that electrolysis at higher pressures takes more energy than doing it at lower pressures, so unless you really need the high pressure, it's a non-starter.

http://en.wikipedia.org/wiki/Nernst_equation

It may come to pass, at some stage in hefutre that with a "hydrogen economy" high pressure electrolysis will be used- but it would be insanely expensive to distribute the hydrogen at such high pressures.
100 PSI- sure, that's already done*
1000 PSI- possibly, but only for very specialist uses
10,000 PSI - not realistic.

*
http://www.hydrogenics.com/hydro/industrial


Of course, it's also important to realise that, just because it can get high pressures, doesn't mean it can be used as a means of propulsion. The flow rate at those pressures is still far too small to get much thrust.
It really is a non-starter.
« Last Edit: 23/02/2013 12:53:52 by Bored chemist »
 

Offline wolfekeeper

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #28 on: 23/02/2013 14:02:09 »
Sigh.

It may be true that high pressures can be made with electrolysis. But that's not what you need for propulsion; you need high pressures over large areas with the minimum amount of propellant.

When you let the gas out, you need some sort of hole. That's an area. If you use a nozzle it turns out it more or less doubles the thrust... at best.

Trouble is, as the gas expands out the nozzle, the gas cools. The hotter the gas is, the more thrust you get and the better the nozzle works, because the gas holds its pressure up better due to the heat.

Also, the hotter the gas is, the more pressure it gives for the same mass of gas in the chamber.

The net upshot is that you really, really, really want hot gas, and that's why virtually all practical engines use combustion to produce hot gas, gas that is as hot as possible.

There is a class of engines called 'cold gas thrusters'. They're used for attitude jets for rockets, but they have very low performance.
 

Offline CliffordK

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #29 on: 23/02/2013 20:23:54 »
I was thinking a bit.

If one had high pressure H2 and high pressure O2.

One could burn the hydrogen using a low pressure oxygen/nitrogen mix from the air.  This would leave the pressurized oxygen to be used as one saw fit.  Of course, with proper controls, there could be a market for it in the welding and medical industries.

Diesel engines inject fuel at high pressures, gasoline engines inject it at low pressures.  It is possible one could gain a minimal amount of energy running the fuel through a pressure reduction turbine before injection.  However, this effect would be quite minimal.
 

Offline wolfekeeper

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #30 on: 23/02/2013 20:45:49 »
If you want the maximum thrust, you just burn the oxygen with the hydrogen and use it to make steam, and stick the steam out a nozzle.

Of course, you get the same thrust as if you had just superheated the water (actually less thrust than that since the electrolysis is extremely inefficient)...
 

Offline Bored chemist

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #31 on: 23/02/2013 21:22:28 »
Here's a rocket engine
http://en.wikipedia.org/wiki/F-1_(rocket_engine)
it delivers 41 Million Watts of power and weighs less than 10 tons.

Good luck with designing an electrolytic cell that can handle that much power and isn't ridiculously heavy.
Incidentally, since the cell voltage is pretty much determined by the chemical reaction and will be about 2 volts we can calculate the electrical current needed to deliver that sort of power.

It's about 20 million amps.
Typically cables handle  about 1000 amps per square inch.
So you need cables with a cross section of about 20000 square inches. That's a square section cable about 350 cm on each side.
A metre of a cable like that would weigh about ten times much as the jet engine.

(Cooling the cell may also be a problem)

" Can Electrolysis Be Used As a Propulsion Method?"
No.
This really is a silly idea.
« Last Edit: 23/02/2013 21:24:59 by Bored chemist »
 

Offline profound

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Re: New No Moving Farts Propulsion System
« Reply #32 on: 03/09/2016 22:40:29 »
Unfortunately, it would generate far, far less thrust than a gas turbine engine or rocket engine of similar mass. It would also require large amounts of electricity for little pay off in terms of thrust.


i understand it can achieve psi of over 10000.A lot more than turbuns,etc.
 

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970041522.pdf

http://www.spacecraftresearch.com/files/ZeledonPeckSpace2011.pdf

you are both wrong again as these research papers prove.

 

Offline alancalverd

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #33 on: 03/09/2016 23:23:11 »
And how do you generate the electricity to electrolyse the water? Nuclear reactors have a reasonably high energy density but then you need a steam cycle driving a turbine and a generator and it all gets very heavy and complicated.

In a ship, you can use the turbine to drive the propellor directly or through an electric motor, but the whole machine won't fly. Better to electrolyse water on the ground, liquefy the hydrogen and oxygen, shove them into tanks in your flying machine, and recombine them in a rocket motor, just like we do already.

If you want a welding gas, electrolyse the water with an alternating current. The stochiometric mixture of hydrogen and oxygen is reasonably stable until ignited, when it turns back to water with the release of loads of heat. "Brown's Gas" welders are quite handy for work in a confined space - not as hot as acetylene but no carbon oxides are produced. Now the question is whether you can liquefy Brown's Gas and make a single-tank liquid rocket motor. Alas, no, because the two elements recombine explosively in the liquid state!   
 

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Re: Can Electrolysis Be Used As a Propulsion Method?
« Reply #33 on: 03/09/2016 23:23:11 »

 

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