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Dave W.
Info Junkie
USA
26022 Posts |
 Posted - 03/08/2007 : 15:31:31 [Permalink]
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quote:
Originally posted by Dr. Mabuse
Bolding mine. Shouldn't that be Energy?
Power is measured in Watts, Energy is Joule (Watts*second)
Yes, energy. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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furshur
SFN Regular
USA
1536 Posts |
Posted - 03/08/2007 : 19:07:17 [Permalink]
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So carrying on this useless endeavor:
This is the work of compressing the gas (in N-m) to raise the bell:
W = Pf x Vf x ln(Vf/Vi)
Pf = 100m of water + atomspheric pressure = 1081738.91 N/m^2 (pa)
Vf = 8m^3. (10,000 kg Bell / 1000kg/m^3 water) - 2 m^3 water displaced by the empty bell.
Vi = 85m^3 PiVi = PfVf Vi = PfVf/Pi (1 atm)
W = 1081738 N/m^2 * 85 m^3 * ln[8/85] Note the ln will yield a negative.
W = -20,451,007 N-m The work is negative because work must be done to compress the air.
Now the bell raises majestically to the surface of the water. Well we actually need just a tad more air to make it more than nuetrally boyant.
At this point the bell is chocked full of PE as shown-
PE = G * m * H
G = 9.81 m/s/s
m = 10,000 kg
H = 100 m
PE = 9,810,000 N-m This is positive because this is available work or energy.
The energy balance is 9,810,000 N-m + (-20,451,007 N-m) =
-10641007 N-m
Why the huge deficit? A lot of the Potential Energy we put into the bell is still available. That is why as klaudio stated the bell will accelerate as the bell rises converting the energy of the compressed gas to KE.
I am getting kicked off the computer I will have to discuss this later.
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If I knew then what I know now then I would know more now than I know. |
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Ghost_Skeptic
SFN Regular
Canada
510 Posts |
Posted - 03/09/2007 : 01:35:14 [Permalink]
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| Furshur - are you assuming adiabatic (no heat loss) or isothermal compression - if the compression is rapid (like the comprssion stroke in an internal combustion energy), it will be nearly adiabatic (temperature of the air will increase as it is compressed) - not that this will make the thing work. |
"You can lead a horse to water but you can't make him drink. / You can send a kid to college but you can't make him think." - B.B. King
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| Edited by - Ghost_Skeptic on 03/09/2007 06:51:18 |
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furshur
SFN Regular
USA
1536 Posts |
Posted - 03/09/2007 : 12:14:04 [Permalink]
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Ghost, I am assuming isothermal. I agree that adiabatic is closer to reality, but I chose the this case because it looks like Kaudio was trying to use the isothermal case - besides it is easier to calculate the work if you choose the isothermal route. Hopefully I can play around with this over the weekend, work has got me hopping pretty good.
This is such an extremely inefficient process that I think you could make about any assumptions and could still not get it above 50% efficient.
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If I knew then what I know now then I would know more now than I know. |
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A flying saucer design
