Expanding property of Compressed Air

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marinesteam
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Re: Expanding property of Compressed Air

Post by marinesteam » Thu Nov 17, 2016 8:02 pm

[/quote]
I was going for the converse that steam is a really good way of transferring energy.

The reason I ask is to try and relate this figure for non steam folks and draw a comparison that for the average modern man(person) is more familiar with now days - compressed air.

-CB[/quote]

But it's really not, that's why we're not driving steam powered cars (among many other reasons) ((If it was we would have figured out the other reasons too))

My guess is anyone who understands how compressed air works already has enough technical knowledge to understand how steam works without the comparison. To most people it's all black magic, mumbo jumbo. I find it best to not muddy the waters with poor analogies and just explain it as it is, answering the questions as needed will make help anyone understand on their own terms.

Ken
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Re: Expanding property of Compressed Air

Post by cyberbadger » Thu Nov 17, 2016 8:30 pm

CB wrote: I was going for the converse that steam is a really good way of transferring energy.
marinesteam wrote: But it's really not, that's why we're not driving steam powered cars (among many other reasons) ((If it was we would have figured out the other reasons too))
Huh? It is a really good way of transferring energy - that's why it's still used extensively in the power generation industry worldwide.

-CB

P.S. Fixed forum quotes.
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marinesteam
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Re: Expanding property of Compressed Air

Post by marinesteam » Fri Nov 18, 2016 1:27 am

Huh? It is a really good way of transferring energy - that's why it's still used extensively in the power generation industry worldwide.

-CB

P.S. Fixed forum quotes.
Apples & Oranges ;-)
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Re: Expanding property of Compressed Air

Post by cyberbadger » Fri Nov 18, 2016 2:27 am

marinesteam wrote: Apples & Oranges ;-)
It's not really Apples & Oranges - it's potential energy.

200PSI Steam Boiler holding 35 gallons of water vs a 35 gallon tank full of compressed air at 200PSI.

One has a lot more energy in it - and energy is certainly something that can be compared between the those two.

-CB
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Re: Expanding property of Compressed Air

Post by fredrosse » Fri Nov 18, 2016 4:57 am

I have to say that the comparison you are trying to make is "apples and oranges", or, in dog terms, "barking up the wrong tree", it is really not a fair comparison in any way as to understanding the processes of thermodynamics and energy transfer.

The reason steam is used to generate electric power (about 85% of all the world's power is made with steam) is because it is the most convenient method that allows burning any fuel, especially solid fuels which are not at all suitable for internal combustion engine cycles using air. With the recent discoveries of plentiful natural gas supplies, internal combustion engines are rapidly replacing coal fired power plants, because these cycles are much more efficient, as well as a smaller "carbon footprint".

In technical terms, yes steam is a very good energy transfer medium, it takes a tremendous quantity of heat to turn water into steam, far more than it takes to obtain a similar heat up of air. The historical reasons for steam power is really tied to the concept of "back-work" In ideal steam cycles, the feed pump uses only about 2% of the engine's output, so a sloppy inefficient steam engine plant will easily still run if the engine only puts out half of its theoretical power, and the feed pump takes twice as much power as it should. Try explaining that to lay people is not generally successful.

In ideal air cycles, Diesels, Otto engines, gas turbines, the "back work", the compression of the air before it is heated within the cycle, is a large fraction of the engine expansion work, so if the compressor, or the expander in these air cycles is poor, they will not run at all. It took until 1912 until they could even get a gas turbine to run, but now they easily exceed steam cycle efficiency.
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Re: Expanding property of Compressed Air

Post by cyberbadger » Fri Nov 18, 2016 6:32 am

fredrosse wrote:I have to say that the comparison you are trying to make is "apples and oranges", or, in dog terms, "barking up the wrong tree", it is really not a fair comparison in any way as to understanding the processes of thermodynamics and energy transfer.
Well I am trying to explain, which has impressed several of those who have steamed up with me, both on Nyitra and previously at home in stationary configurations, is the amount of energy contained in my VFT when I am at 200PSI compared to the closest analog I can think of which is a compressed air tank.

One time I had a Steam siren on my old dry-bottom non-code vft that I was going to try with a few other things and the valve on that darned siren stuck open and I had no isolation valve(Lesson Learned)... It was already making more noise then I was comfortable with continuously emitting onto the street. So I had to dump the fire, then dump steam until I got to a lower pressure and could just blow the boiler down.

I carry fully opened some valves and my cousin was shocked just how long it took to get the pressure down....

So I like to think of it as storing a lot of potential energy when under steam. Maybe I can compare the amount of energy to how many kilocalories(nutritional calories) instead. :)

-CB
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Re: Expanding property of Compressed Air

Post by TahoeSteam » Fri Nov 18, 2016 7:24 am

Well to raise your 35gallons from about 60*F to 388*F (steam temp at 200psi) it would require about 96,000 BTUs, or about 24,192 calories...

You can figure out how to convert your compressed air into calories and get an number to divide the steam calorie count by to derive your factor of power...
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Re: Expanding property of Compressed Air

Post by DetroiTug » Fri Nov 18, 2016 11:19 am

Propane and similar gases would be the closest thermal conversion of liquid to gas comparison. Propane boils at -44 degrees F and water boils at 212 degrees F and requires an additional heat source to do so here on earth. Someday when we live on Mars and have really efficient air conditioning for our steam boats or humans have adapted to higher temperatures and breathing sulfuric acid, ambient temperature will suffice..

Yes, compressed air is stored energy, but it is simply storing a gas liken to compressing a spring with very poor temper, never able to fully store the energy it took to compress it.

Compressed air as you suggest is mechanically compressed gas with loss and nothing more. Heat has little effect upon it.

Steam is a thermal conversion and vaporization of liquid to gas. No heat, no energy. Temperature must remain constant to "store" it.

Yes, both can be "stored" energy, but that is where any comparison between the two stops.

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Re: Expanding property of Compressed Air

Post by ccdewitt » Fri Nov 25, 2016 10:04 pm

The comparison of compressed air and pressurized high temperature steam could be considered analogous to comparing a one pound compression spring and one pound of gunpowder. Certainly one system has more potential energy compared to the other but outside of that there is no practical comparison. So rather than trying to equate the two just explain what each is and how they work. Don’t forget to include the discussion of latent heat as that is a large part of the stored energy in steam.
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Re: Expanding property of Compressed Air

Post by cyberbadger » Sat Nov 26, 2016 2:32 am

I basically agree to disagree with everyone and I'm half sorry I brought it up. :)

-CB
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