oxygen concentrator, pressure swing absorption, system

[BazyleParticipant @bazyle]

On a more interesting note my minimal research is showing that there are sieves capable of letting O2 through and stopping N2, then the OP's original proposal of a material that absorbs O2 from air under pressure and can then release it later on. Wow! I'm impressed that such things have been invented, and seem to be potentially available to us amateurs.
Then I found a Stirling engine running in reverse that can get cold enough to liquefy air. These are apparently quite common in mobile phone towers (so lots of them) for cooling the electronics. Such an engine also might be within the capabilities of a model engineer.

Worth considering that many of these machines if not needing an industrial scale to work are initially developed in university research labs which are staffed by the equivalent of skilled model engineer machinists using the same machines that we have in our sheds. Therefore all eminently do-able.

[Carl Wilson 4Participant @carlwilson4]

It really is astonishing what can be done. In my research into rocket engines I have done extensive reading into the progress made by the Germans in Ww2. If you can download a copy of the report into Operation Backfire, do so. Fascinating reading.

What they managed with scant resources, basic equipment and skill and ingenuity was astounding.

[Brian OldfordParticipant @brianoldford70365]

Shout me down and tell me I've missed something if you will, but couldn't oxygen be produced more easily by electrolysis of water perhaps?

[not done it yetParticipant @notdoneityet]

5 litres per minute of approx 90% purity, using only approx 300W power input will far out-perform electrolysis, I would guess. Electrolysis would make exactly the right amount of hydrogen for the rocket fuel, mind!

 

Hydrolysis purity would be 100% after drying, but for volume oxygen concentration, the pressure adsorption method will win hands down on running costs.

Edited By not done it yet on 10/10/2016 18:47:30

[JAParticipant @ja]

Moving off topic, sorry

Posted by not done it yet on 10/10/2016 18:46:49:

5 litres per minute of approx 90% purity, using only approx 300W power input will far out-perform electrolysis, I would guess. Electrolysis would make exactly the right amount of hydrogen for the rocket fuel, mind!

No. Because of specific impulse considerations the rocket would run fuel rich. To assess the performance of a rocket engine the mass of the fuel and oxidant must be considered along with their energy output. Although the ratio of hydrogen and oxygen produced by electrolysis would be the most energetic using more hydrogen gives a better specific impulse, measure of potential performance, because of the lighter "payload". Hydrogen Oxygen gives the second best chemical specific impulse, the best is Hydrogen Fluorine. This has been used in small research engines!

Bazyle – Did not James Watt develop his engine at Glasgow University as a model maker.

JA

Edited By JA on 10/10/2016 19:40:59

Edited By JA on 10/10/2016 19:43:54

[SillyOldDufferModerator @sillyoldduffer]

Posted by Carl Wilson 4 on 10/10/2016 17:26:26:
Dave,

You are right, I overreacted and for that I apologise.

I agree strongly with you that what Paul has done is a great achievement. My interest lie in experimental rocket engines and the possibility of producing liquid air, albeit slowly, is a very exciting one.

I'm just wondering if the process would be noisy due to the gas going supersonic in the nozzle. Then again, the nozzle/orifice is surrounded by a thick blanket of insulation, from what I can see. That should dampen any noise there might be.

Hi Carl,

Thanks for your response, no problem.

If you're into rockets and can handle it liquid fuel is the way to go. Not easy to do but then it is Rocket Science.

I'd be tempted to start with a gas that's easier to liquefy than Oxygen. Nitrous Oxide is used in performance engines so it must be possible to buy it by the cylinder. I don't know what the legalities are and Health & Safety would be an issue too.

However, the advantage of Oxygen is that its free. The hardest part is the compressor. Once you have compressed air, it can be pre-cooled and then expanded to drop the temperature. Part of the trick is using air cooled by expansion (any that doesn't liquefy) to cool the incoming pipework. The whole installation needs to be very well insulated with arrangements for drying the air and removing unwanted constituents like Carbon Dioxide. This paper may be helpful.

I don't know how noisy expanding a gas to cool it would be, or how loud the compressor is. My little workshop compressor certainly makes a racket.

Once you have liquid oxygen you need a vessel to store it in, and then a way of safely loading it into the rocket.

Firing the rocket is another problem: you will probably need to pump the fuel and oxygen into the engine and then ignite it. Finding a way to pump liquid Oxygen stretched the pioneers, though the early Goddard rockets look simple enough. After firing the worst thing that can happen is a "soft-start". If the rocket doesn't light up immediately a mass of fuel-oxygen mix builds up and turns the launch into an explosion. Ouch.

With so many technical problems to overcome it feels to me like Rocketry is a team sport. If you haven't done so already the UKRA may be worth a look.

My interest is a lot easier. I'd be very pleased if I managed to liquefy a just few drops of air as a novelty. It would be a real achievement and it might even impress a few of my friends – or not…

Cheers,

Dave

[not done it yetParticipant @notdoneityet]

No. Because of specific impulse considerations the rocket

Isn't he building a furnace to melt metal? Not trying to go to the moon, is he?

[JAParticipant @ja]

Posted by not done it yet on 10/10/2016 22:18:00:

No. Because of specific impulse considerations the rocket

Isn't he building a furnace to melt metal? Not trying to go to the moon, is he?

Sorry, moved off topic!

JA

[Carl Wilson 4Participant @carlwilson4]

Hello,

I'm well on the way in my rocket engine developments thanks. I am using nitrous oxide. It is possible to buy in a cylinder, I have one. The UKRA mainly deals with solids so not really what I'm doing. At the moment my project is the only liquid fuelled amateur rocket engine effort in the UK, as far as I know. It is also the only amateur liquid fuel engine design using a tube bundle construction.

You can't store liquid oxygen legally in the UK without the correct facilities. As a former aircraft engineer trained in it's handling and use I do not recommend it.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Carl Wilson 4 on 11/10/2016 00:15:10:

…

I'm well on the way in my rocket engine developments thanks. I am using nitrous oxide. .

…

Always a danger on this site that I might blunder into telling Granny how to suck eggs!

Reminds me I once spent 10 minutes on an IT Course explaining British 3-pin plugs to a Norwegian. Of course he turned out to be an electrical engineer who spoke better English than me…

Sorry for making a foolish assumption in your case too. I'd better stick to the Coke Bottle thread.

Have you had much success yet? Rockets are very interesting.

Dave

[Carl Wilson 4Participant @carlwilson4]

Hello Dave,

Don't worry. I was more than impressed by your willingness to help and by the time and effort you put in to researching the subject to answer someones question.

If I had been a beginner then I would have come away with a wealth of information and resources. That is what the site is all about, and it is thanks to people like you with your willingness to share your knowledge and time.

My rocket project makes slow but steady progress. At the moment I'm engaged in research to test the strength of TIG welded aluminium structures after I have solution treated then artificially aged them in a pottery kiln that I am using as a heat treatment oven.

[SillyOldDufferModerator @sillyoldduffer]

Posted by Carl Wilson 4 on 12/10/2016 17:18:22:.

…

My rocket project makes slow but steady progress. At the moment I'm engaged in research to test the strength of TIG welded aluminium structures after I have solution treated then artificially aged them in a pottery kiln that I am using as a heat treatment oven.

That's remarkable work.

When I was a schoolboy there was a V2 on display in the Science Museum that I was able to reach and poke with my finger. The skin gave amazingly easily – not unlike prodding an empty aluminium drinks can. Somehow I expected a weapon designed to go supersonic with a 1 tonne warhead to be much more heavily built. Minimising the weight of a rocket's structure whilst ensuring it's strong enough to do the job must be engineering at the extreme.

I wish you every success!

Dave

Edited By SillyOldDuffer on 12/10/2016 17:47:35

[Stuart BridgerParticipant @stuartbridger82290]

For a rather long and detailed, but fascinating read on the history of rocket fuels Check this out

https://library.sciencemadness.org/library/books/ignition.pdf

Stuart

 

Edited By Stuart Bridger on 12/10/2016 18:05:46

[Carl Wilson 4Participant @carlwilson4]

That is a good read. However, the section on hydrogen peroxide should be taken with a pinch of salt.

The attitude of the Americans to this substance is downright hostile and this is due to a lack of knowledge and operational experience.

After the Germans in Ww2, Britain became the expert in hydrogen peroxide propulsion systems. We launched a satellite using them in the early 70s.

[Carl Wilson 4Participant @carlwilson4]

Dave,

Yes, I have had a fascination with the V2 for years. So have a lot of others. Practically every rocket the U S launched up to the Apologies programme was just a big V2.

If you are interested it is now possible to download the complete report (5 volumes) of operation Backfire. This was the British study of the V2 carried out in 1945. British Technical Intelligence and Reme personell were assisted by captured Germans in studying and firing several missiles.

[Carl Wilson 4Participant @carlwilson4]

Apologies = Apollo!

[SillyOldDufferModerator @sillyoldduffer]

…

download the complete report (5 volumes) of operation Backfire.

….

Many thanks for that – just got 60Mb of my kind of thing to read.

[Carl Wilson 4Participant @carlwilson4]

Set aside a couple of days to go through it all. You will not be disappointed.

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