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John Bushnell
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I am developing a novel approach for using gravity to compress air.
Do you know where I can buy an electrical generators that is driven by compressed air?
 
Dale Hodgins
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John Bushnell
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HI Dale,
Thank you for your response.

No it is not a Trompe system.

I was thinking that there may already be air motors coupled to electrical generators on the market.
Thanks again,
John
 
David Livingston
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Its not as easy as it sounds as the changes in pressure have heat effects . That is what sunk the idea for an Air car . ( a car powered by compressed air ) To show you what I mean have you noticed when you pump up you bike wheel how the pump can get hot ?

David
 
John Bushnell
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HI David,
So are your saying;
if you pump air into a storage tank, like your bike wheel, then the increased pressure results in an increase in the temperature.

Then;

If I am driving an air motor from a compressed air storage tank (not the bike tire) & The air flowing across the motor is expanding not compressing,

so then are you saying that the motor will experience heat gain from the decompressing air flow?
Thanks,
John
 
Daniel Schmidt
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The heating occurs at the time of compression. The molecules being jammed into each other creates friction and therefore heat (as well as friction in the compression device). Decompression will cause cooling. Where I live it is extremely humid, and when I was framing houses we would unhook an air tank from the compressor and it would ice up. The point at where the decompression occurs works just like an air conditioning unit, and moisture in the system can turn to ice which can cause problems.
 
David Livingston
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The problem with these heat changes is that eventually because different rates of expansion and contraction between the different materials involved that you get seals braking loose pressure etc etc .

David
 
Troy Rhodes
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The compression/heating effect of air (that's how diesel engines ignite the fuel) can cause frost problems on the use or decompression side, and may also reduce real world efficiency.

Let's say you compress a gas to 500 psi. It takes a lot of energy to do that, and it's not -really- 500 psi because some of the increased pressure comes from the increased temperature. The increased temperature -will- go away, either as the tank cools off if you're saving it for later, or on the expansion cycle when you immediately use the compressed hot air. As the cooling occurs, you lose some of the apparent pressure as well.

Compressed air as a medium to transmit power is pretty lossy, primarily from the friction/piping losses, and secondarily from the heating/cooling effects on the real temperature/pressure.

That doesn't mean compressed air isn't useful and worthwhile, it gets used for a ton of things. It's just not super efficient at transmitting energy. If you have a method to produce compressed air cheaply and efficiently, the whole world will be interested.

As an exercise, I once did some back-of-the-napkin calculations to use some of the waste heat from the hot end of a big compressor using TEGS (Thermo Electric Generator units). The resultant electricity was (as I recall) well over three dollars per kilowatt hour.

So, while my idea was novel, and would "work", it wasn't useful. I hope yours has far better math than mine did.
 
John Bushnell
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Thank you Troy,

Very Insightful information.

I have not seen the novel approach to compress air that I'm talking about anywhere.

Yes, the first things that I'm trying to do is determine if it is a cost-effective approach when compared to other methods of compressing air.

So I want to start with the conventional side of the equation, and speak of this method as "a tank of compressed air."

Then a volume of air is drawn from the tank to drive a motor that is coupled to a generator.

Now this tank can be as large as I want, and it can have pressures as high as the tank (and seals) can handle.

One of the down sides of this method is that in order to recharge the tank,
it has one piston that can be designed to deliver as high of pressure as is physically possible, however it has only one short stroke per cycle and
then it will take a few minutes for the next stroke.

So the tank needs to be pre charged and not go below a set PSI as air is drawn out to run the motor.
Again the piston that charges the tank can deliver above 100,000 psi in a stroke.

Since P-1 X V-1 = P-2 X V-2 Then if we start with a high P-1 and take it super higher with P-2 the relative change between V-1 and V-2 will be small.
Therefore will sustain a constant cfm to a motor until the next stroke.

So as I have time, I need to find out what some conventional air motor requirements are; in terms of CFM and PSI.

Thank again for your insight,
John

 
Troy Rhodes
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The air motor side is a robust and mature technology, with a lot of offerings from pretty small to pretty big. Just to give some preliminary data, here's a 4 hp motor:

http://www.ebay.com/itm/GAST-6AM-NRV-63-Air-Motor-4-HP-128-cfm-3000-rpm-/381023015359?hash=item58b6bdd1bf:g:y-wAAOSwzhVWrQeJ


and a 3/4 hp motor:

http://www.ebay.com/itm/GAST-2AM-NCC-96-Air-Motor-0-75-HP-30-cfm-3000-rpm-/331345994607?hash=item4d25c2a36f:g:GhAAAOSw--1WrUS8


both list cfm and pressure requirements.

 
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