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From my article:"Fluid is stored in a low-pressure reservoir. A pump moves the fluid from the reservoir to a high-pressure accumulator."Oh. I wasn't expecting that at all (!?).That's the trouble with glimpsing an idea on the web & then (later) looking for another article to illustrate your point/question, I guess Saying that I'm (almost) sure the first article I read was purely pneumatic, with HP & LP cylinders acting as the differential-pressure energy storage - as opposed to medium pressure and outside air pressure. Would this make sense or am I delusional?
I suppose the big issue is how much energy can be stored in the high pressure accumulator.
Quote from: Geezer on 02/06/2010 07:20:14I suppose the big issue is how much energy can be stored in the high pressure accumulator. Here:http://en.wikipedia.org/wiki/Energy_densityindicates 4MJ/kg for 300bar...compared with 0.72MJ/kg for Li-ion batteries.Still looking for that original article. But I have a feeling there might be some sense to running from a, say 100 bar tank to a 400 bar tank over 1 bar to 300 (if only for stationary apps). 
If I understand the tables correctly, the 4MJ/kg for compressed air does not include the mass of the storage tank.
What would be the advantage in pressurizing both tanks? Would that not just mean there was some stored energy that could not do work?
To explain:System A consists of a high pressure (30MPa) tank driving a (ideal) pneumatic motor expelling spent air to an ambient pressure reservoir (ie. the outside air).System B consists of a higher pressure (40MPa) tank driving the same motor expelling to an intermediate pressure (10MPa) reservoir.Both systems could then be recharged by running in reverse.I would think that the work available in both systems is equivalent... Is this true?
I think the work would be equivalent, but I'm not sure what advantage B would have over A. Why go to the trouble of having two tanks when one would do?
Quote from: Geezer on 04/06/2010 20:25:12I think the work would be equivalent, but I'm not sure what advantage B would have over A. Why go to the trouble of having two tanks when one would do?Neither do I and having been unable to locate the original article, it must have come from a (boring) dream Just a thought: Is the heating/cooling of gases in A and B also equivalent?
I use a tool at www.thermofluids.net It's worth checking out.
That was really worth reading and the explanation was really awesome. I got so much of information about accumulator. I don't know that from where the energy in compression is gain but all had explain it very well, good job done by you.