Naked Science Forum
General Science => General Science => Topic started by: birdzoom on 12/02/2013 17:48:06
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Could lighter-than-air craft platforms in the oceans lift vast amounts of water high enough that they could then produce energy in the form of work?
The problem I see is in how to make the platforms come down without making it all counter-productive.
I think very light but strong materials may be developed in the future that allow these platforms to be vacuous, so they wouldn't need to be filled with a very light gas like helium.
But even though costs could make it prohibitive and it be a very inefficient concept, and unfortunately you would probably have to use energy from other source to make the platforms come down, which is a serious flaw in the concept.
What do you think? Is there something to this idea?
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I presume you mean using hot-air or helium filled baloons to lift a lightweight vessel full of water.
Sure, if you could attach enough baloons to an olympic swimming pool it would lift it, but the energy used to produce lift would be greater than the energy harvested.
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Clouds? And some sort of modified Kelvin water dropper to extract the energy from the clouds (without trying to "capture" lightning)??
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Clouds? And some sort of modified Kelvin water dropper to extract the energy from the clouds (without trying to "capture" lightning)??
No good trying to patent that idea, the Sun got there first.
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I'm fairly sure that the energy expended to inflate the balloon (and therefore push back the atmosphere) is exactly the same as that which could be obtained from whatever the balloon could lift.
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Water is, in fact, lighter than air.
Well, at least in its vapor form.
One could, in theory, build a balloon filled with a hot air/water mix. Perhaps paint it black so that it can be heated by the sun, and then cool at night, or cool by turning a silvered side towards the sun.
Anyway, use solar heat to evaporate your water while warming & expanding the air in the balloon, then block the sun (and also use the cool upper atmosphere) to cool it, and re-condense the water. And, then allow it to fall back down. One could maintain an air/water vapor mix at a lower temperature than pure water vapor.
Efficiently building an engine using this method might be far more complicated.
I'm trying to think of other lighter than air gases with a relatively high boiling point that could also be used. The list is relatively short.
Two come to mind.
Ammonia/Water Mix.
Hydrogen Fluoride/Water mix.
(not to be mixed together, of course [xx(]).
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Water is, in fact, lighter than air.
Well, at least in its vapor form.
One could, in theory, build a balloon filled with a hot air/water mix. Perhaps paint it black so that it can be heated by the sun, and then cool at night, or cool by turning a silvered side towards the sun.
Would it not be easier to simply control the rise of water vapour and capture the precipitation?
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Though I'm not sure if it might be more effective to dispense with the whole contraption and just excavate a large reservouir in a mountainous region with high rainfall and have a hydro-electric damn at one end.
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Your apparatus may work.
It likely would have to be quite tall... as tall as the mountains!!!! As shade on a warm day would likely not give you enough condensation. And, since condensation gives off heat, you couldn't simply insulate the condensation chamber. Anyway, it would be good to go from warmer valleys to cooler mountain peaks (not too cool though, ice may not be desirable).
I'd probably make it a closed system as you could likely better heat a small evaporation chamber, rather than expecting the sun to effectively heat a larger body of water. Keeping in mind, of course, that evaporation causes cooling.
One can alter the vapor pressure or evaporation rate somewhat by messing with the pressure (another reason to use a closed system).
NH3 or HF, or CH4 might be effective under a rather high pressure.
However, your water evaporator/condenser may work best under low pressure conditions.
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Indeed, it would need to be very tall to take advantage of lower temperatures at higher altitudes. It would also need to be on quite a vast scale to be of any real use.
I did wonder whether it should be a closed system, but thought pressure changes might be a problem. If it is to be a contiuous circulatory system, I questioned whether artificial alteration to pressures would be possible. The introduction of valves and pumps to maintain unequal pressure thoughout the system would inhibit the free flow of vapour and condensed water and probably use all the energy the system produced just run the system, hence I concluded the system needs to be powered purely by solar power and temperature fluctuation between ground level and high altitude, leaving presure changes due to evapouration, condensation and altitude to nature.
But, to be honest, I think that even it worked, it would not be capable of producing sufficient energy to make such a vast structure and its maintenence requirements viable.
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A method to build a hydroelectric facility is to build pipes to supply water to the generator.
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source (http://www.freeimageslive.co.uk/free_stock_image/hydroelectric-water-pipes-jpg)
Where the long pipes create pressure, more or less equivalent to a deep reservoir.
The problem is that with a passive evaporative system, the pipe carrying the water vapor uphill would have to be greatly oversized due to the lower vapor density.
I don't see a closed system being a problem, although it might require an additional pipe to carry cold, dry air back down the mountain.
One may have to build a system to prevent a vacuum from forming. If running at ambient pressure, the pressure would be more or less the same in the pipe as outside, even through elevation changes. Temperature changes could create different vapor densities (which might be good).
I agree that there are generally benefits of allowing Nature to do the work carrying the water up the hills.
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People already do this; they're called gliders!
Gliders are powered by heated air, but also heated water vapour; they spiral up in an updraft and can go for many miles.
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If you had two lakes one 100m higher than the other then it would work.
The lower lake shallow and wide black painted bottom or black dye enclosed in some kind of green house. perhaps lots of artificial little black ferns on the surface sucking up water via capilary action and evaporating it at the leaf surface.
The upper lake covered in a reflective dome
If you had a set up like this in the death valley it might just work. The EROEI probably low but in theory it could be positive. The bigger the height difference the easier it is to capture the energy of falling water.
The maximum height difference of a solid structure in earths gravity is about 10 miles. +5 miles mount Everest ( which is slowly sinking ) -5 miles, deep mine ( whose walls are slowly buckling inwards) A lighter stronger material than rock might achieve a 10 miles tall structure that is stable. aka immune to sinking and buckling for thousands of years.....you can get quite a few tons of pressure for every square centimeter of water turbine-blade if the height drop is large enough.
The Nurek Dam, Tajikistan - the tallest dam in the world
Thermal tower
http://ecofriend.com/wp-content/uploads/2012/07/charlwood-design-solar-tower_1_ipdTt_69.jpg
Solar balloon
http://en.wikipedia.org/wiki/Solar_balloon