Air-powered cars..... Re: attn PV if he's still around.

"Existential Angst" fired this volley in news:4d155274$0$32228$ snipped-for-privacy@cv.net:

Can't remember which author OR book, now, but there was a SciFi that depicted a world where all transportable energy sources were by giant springs -- except with some futuristic molecular science in them that allowed a single spring that could reasonably fit in a small vehicle power same for hundreds of miles.

I can't remember the story exactly, but it was about a rebellion on a colony planet. The colonizing society was high-tech, but the colony was forced to be low-tech; thus the spring-wound transportation.

LLoyd

Long ago, I think it was in England, they had something I think it was called a Penny Farthing, something like that, I think.It was a wind up spring motor for bicycles. Long before that, a guy in Italy invented some sort of a wind up spring 'car', or at least he sketched it on paper. cuhulin

Perhaps David Brin's "The Practice Effect"?

FYI, we didnt use mpkw. It was normally litres per 10 kilometers driven. Other countries might use other units.

Litres per 100 Km.

I will remind all that businesses usually try to avoid the use of compressed air for things like tools when possible. It's a very expensive & wasteful mode of power distribution.

Well, if this is true, then the air car is doomed. :(

There are also compression losses itself, from the heat produced (pv = nRT), but I was under the impression those would be relatively minor, altho I haven't done the calcs. Theoretically, in an insulated tank, this really wouldn't be a loss, but insulation is indeed a pita.

It could be that the rotor losses are indeed substantial. For example, the energy retrieved from wind energy is only about 50%, because of the "dead" air at the blades, etc. I sort of assumed that in an engine, they would have greatly reduced these losses, but mebbe not.

In the original features of the french guy designing this air car, they claimed that it cost like $2 for an air charge that was good for a whole bunch of miles, amounting to a *fraction* of the gasoline cost.

And yeah, it seems reasonable that an air tool WOULD be substantially less efficient than an electric tool, as there are losses in BOTH directions: compressing the air, AND delivering the air through the tool rotor, whereas the electricity used to compress that air can just drive the tool directly, at near-100% efficiency.

Heh, mebbe batteries ARE the way to go.... but the problem there is the PRICE.... holy s*it..... No free lunch, eh??

Air Car = Cold Fusion??? No real excuse for all these ambiguities....

Mebbe a big-assed spring is an answer...... But be careful with that, you'll poke yer eye out.... (Xmas Story.....)

Let's see you could get a boiler and some water and coal and use the steam to run it, I think we just invented that Stanly Steamer II

But it takes at least a few minutes to get going from a cold start - not acceptable, unless there's an answer to that.

The old Doble Steam Cars.I would like to see steam cars make a come back, with modern day technology.

How does a flash boiler work? cuhulin

"Impedance" matching limits conversion efficiency too IIRC. In some cases 50% is the maximum possible conversion efficiency.

Um no.

Compressing and expanding air (or any gas) produces and absorbs heat respectively. That is a massive loss of energy.

Do not forget that air compressing machinery has friction losses as does the expansion mechanism.

Um, pt 1 is correck, it's not Carnot....

Pt 2: Just how big ARE these heat losses?

pV = nRT.... mebbe p1v1/T1 = p2v2/T2, solve for T2, then E = mcdelta T as the energy lost?? Heh, but what's V1?????

Could just measure T2..... how hot is hot??

But since m and c for any gas are pretty small, the total energy is pretty small. I mean, we're talking a delta T of, what, mebbe 100 deg? 200 deg? Still a very small E.

I personally think the blade losses, as in a windmill, would swamp the heat losses due to compression.

Sorry if I implied that it was.

I looked at running some numbers but quickly got in over my head so I fell back to MIL-STD-1522A, page 10, which gives a chart of potential energy verses pressure.

The classic example is 2 tanks, equal volumes connected with a valve. Pressurize one to n psia, the other to zero psia, calculate total energy, open valve, recalculate total energy. As I understood your original statement, the total potential energy should stay the same.

From the chart in MIL-STD-1522A you can work out that if n=100, you lose 30% of your energy and with n=1000 you lose 10%. Not as huge as I expected, but not negligible either.