h a l f b a k e r yTrying to contain nuts.
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Inspired by [django] and his congo river-fridge.
It's late and I'm sleep deprived, which means only one thing: post an idea on the HB with one eye (half) open.
Take one large-enough blimp, add tether designed to carry refrigerant in a continuous loop within its insulated cable, bolt some renewable
power to the blimp to run a small pump (like wind gen or solar), top off with heat exchangers at either end of the tether.
Launch blimp to a height where things are chilly (and it can support the weight of the tether). Start.
If all goes ok, refrigerant should vapourize when passed through ground-HX, the rush up the tether as a gas where it would be rapidly cooled in the blimp-HX, change phase back into a liquid then run down the tether back to the ground-HX.
People on ground now have a place to put their heat.
Stirling blimp
Stirling_20High_20Altitude_20Blimp
Shameless blimp-promotion [django, May 07 2008]
Cosmic Background Refrigeration
Cosmic_20Background_20Refrigeration
Shameless cooling promotion [BunsenHoneydew, May 21 2008]
[1] Atmosphere Of The Earth
http://en.wikipedia...e_of_the_atmosphere
pikiwedia [BunsenHoneydew, Nov 29 2010]
[2] Pressure by altitude
http://en.wikipedia..._pressure_variation
[BunsenHoneydew, Nov 29 2010]
[3] Snow line
http://en.wikipedia.org/wiki/Snow_line
[BunsenHoneydew, Nov 29 2010]
[4] Space Shuttle LH2 tank
http://en.wikipedia...ical_specifications
[BunsenHoneydew, Nov 29 2010]
Acoustic lubrication
http://en.wikipedia...coustic_lubrication
Unfortunately, this would also add heat to the system. [BunsenHoneydew, Nov 29 2010]
For only pennies...
Category_20Consulting_20Ltd_2e
[normzone, Aug 09 2016]
[link]
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It would have to go pretty high, but it's a good solution. |
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Interesting concept. The very low temperatures at high altitude can even power a blimp based on a solar dish-coupled stirling engine [see link - but please consult the picture]. |
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Alternatively you can store fruits and vegetables in the blimp and bring it down each time you need a banana. |
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Or train a monkey to climb up and get the banana for you. |
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They will be too busy typing, methinks. |
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Utter genius [+]. I'd like to negotiate a license and/or technology exchange program for your blimp technology to integrate it into my Cosmic Background Refrigeration [link] |
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Is the blimp designed to discard heat by radiation (to the sky), or by conduction/convection (to the surrounding air)? |
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Note that if we can get the blimp up to the stratosphere, and provide radiative insulation (to protect it from the heat of sunlight and earthlight), we should be able to cool even during the day. |
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A good idea, but to be honest, I mainly gave you the
croissant for the name. Fridge Blimp. Perhaps it could
be built in the shape of a huge cube! |
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"Daddy?"
"Yes, Dennis?"
"What is that huge cube in the sky?"
"Oh but of course Dennis, that huge cube is a fridge
blimp!" |
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How much heat can be extracted from the blimp if the
atmosphere is thin? |
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I though 'fridge blimp' would be an epithet for a person whose shape was testiment to too close an attachment to said whitegood and its contents. |
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[MaxwellBuchanan]: if it's substantially above the atmosphere's greenhouse gases, designed to cool by radiation, and shielded from the sun, moon and radiant heat from below, quite a lot; as per arguments at Cosmic Background Refrigeration, you could in theory approach 3°K. |
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The balloon itself could function as the radiant HX: a mylar hemisphere suspended a few inches below to shield it from the Earth's radiance; the upturned cup shape will naturally fill with cold air, thus providing a level of conductive cooling; the bottom half of the balloon itself silvered internally to reflect radiant heat from the gases upwards, and steerable external sun- and moon-shields. |
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Unless there is some *very* good insulation in the tether, the inside will function as a counter-flow heat exchanger, while the outside allows the fluids to go to local atmospheric temperature. |
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There is still potential for power generation, however, given that the insulation in the tether is sufficiently good. |
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Yes, there is great potential, but the insulation is a bigger factor than it first seems. Five miles of piping is going to lose a lot of heat. |
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I propose, instead of the return line, that the cold liquid is put into insulated containers and dropped quickly to the ground. |
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In order to get high enough, you're going to start hitting the tensile strength limits of wire or tube, especially since the tube will be carrying liquid or gas refrigerant. If you have a blimp 5,000 ft up that means you would have 10,000 ft of line. even at a tiny straw sized tube you would still have hundreds of gallons of coolant if not more. assuming a density of water, 100 gallons of water weighs 800 pounds. Add in the weight of the wire and tube, the blimp will be so big you might as well live in the shade and use that to lower your heating bill. |
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Simple answer to the weight issue: use gaseous hydrogen * as your coolant. Apparently it's a rather good thermal transfer medium. |
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* Or indeed any other gas which, when heated, is both lighter than air, and can maintain the gaseous phase until it reaches the upper HX. Bear in mind that external air pressure drops with altitude, and thus you can avoid inadvertent liquefaction in the hot line for longer. Nitrogen and oxygen are possible candidates - being the major components of air, any heating will make them buoyant, and they liquefy at a relatively toasty 63 and 90°K respectively (vis 20K for H2). Heck, air itself liquefies at 78°K. |
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Nevertheless, H2 has the decided advantage that it remains buoyant even at ambient temperatures and pressure, and in both the hot and cold line (sans liquefaction). This property makes it useful for cooling a much wider range of heat sources - from nuclear reactors on down. Helium, ditto. I will hereon use H2 merely as a shorthand for "suitable buoyant refrigerant X ", although I think it is likely to be the best candidate. |
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Make your hose wider, indeed the wider the better, as you get more internal volume per surface area insulation required. Say a 12" ID surrounded by a couple of inches of layered aerogel and mylar, and all wrapped in kevlar (for the tether). Those figures are a wild guess; the object of the game is to strike a balance where a given cross-section of hose/tether/insulation/coolant is at least neutrally buoyant. You may need to widen the hose as it rises to compensate for both lost heat (and thus buoyancy) and the thinning atmosphere. Similarly, insulation requirements will vary with the outside ambient temperature. |
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The entire device could simply be a giant loop of hose, sans "blimp" per se - insulated on the way up and down, and exposed to the outside air (or set up as a linear CBR) at the top. |
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The one slight disadvantage is that you then have to pump the H2 back down the return line, but I still think you come out ahead. Unless it's cold enough to liquefy - in which case the return line would be massively narrower internally (yet require massively more insulation). |
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// I propose, instead of the return line, that the cold liquid is put into insulated containers and dropped quickly to the ground. // |
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If you're using water, freeze it solid in aerodynamically shaped moulds, and tip the resulting iceblocks overboard. Saves having to haul new containers up all the time. |
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Although I must admit the notion of giant dewars of liquid hydrogen air-dropping down from the edge of space is rather appealing - and with steerable fins, wings or chutes, makes for a rather terrifying weapons system. High altitude BLEVE bombs, anyone? |
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// It would have to go pretty high // [wagster] |
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At what altitude is one above 90% of the Earth's CO2? |
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// In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence. The homosphere includes the troposphere, stratosphere, and mesosphere. |
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/ The troposphere begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator / The troposphere contains roughly 80% of the mass of the atmosphere. |
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/ The stratosphere extends to about 51 km (170,000 ft). Temperature increases with height / at [the stratopause] 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000 sea level. // [link 1] |
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So, despite my initial assumption, greenhouse gases do not sort by weight until far beyond any practical height. To get above 90% of the GHGs, we thus need to get above 90% of the air - or, to an altitude where ambient pressure is 100millibars. According to [link 2] that is at 16,000m (53,000ft). |
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The fact that the troposphere is thinnest at the poles is interesting, given that (if we consider the fridge blimp as a greenhouse mitigation geoengineering strategy) the poles are where the greatest relative rises in temperature are expected, and have been observed. A mesh of H2 coolant hoses could be laid out over vulnerable glaciers to keep them cold and stable. It's a two-for-one deal - save the glaciers, and cool the atmosphere overall. |
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But let's split the difference, and assume that the first fridge blimps would be sited over the industrialised northern temperate regions (between 30º and 60º north). We can assume roughly that the 16km average figure is the actual optimum height at these latitudes. |
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That is indeed a long tether (not even accounting for the blimp's wind-blown drift to the side), but it's no space elevator, and if the tether/coolant line is neutrally buoyant (as above) the stresses involved should be manageable. |
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Indeed, if the aim is merely to dump heat into cold air, we would not need to go anywhere near as high. Anywhere cooler than the ground will do. |
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Indeed, they could be staged, and each stage could use different refrigerants. A steam/water cycle to an atmospheric HX blimp below the local snow line [3] (to avoid freezing), and a secondary H2-cycle to a CBR HX blimp in the stratosphere; perhaps a third in between at the tropopause (the coldest altitude according to [1]). |
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// Unless there is some *very* good insulation in the tether, the inside will function as a counter-flow heat exchanger / [baconbrain] |
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Make the hot and cold lines completely separate. They could be kept apart a foot or so with lightweight nylon rods, and/or the cold line could hang below the hot line. |
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If instead the hot and cold lines are completely separate, you could geographically separate the anchor points as well; that would help with the blimp's station-keeping. One site could receive cold refrigerant from a blimp to the east (say) and pipe hot refrigerant up to a blimp to the west. Arrange a number of them in a ring to close the loop. |
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Or, if the "blimp" is a long, semi-rigid horizontal tube (for maximum cooling area), the separate lines can return to the same point; the entire apparatus looking like an inverted triangle. |
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I note that the Space Shuttle's external LH2 tank [4] is only pressure rated to 32–34 psi (220–230 kPa) (absolute). Given that's around the pressure of a car tyre, and it maintains H2 as a liquid for long enough to standby and launch using only spray foam, an LH2 return line seems within sight of engineering feasibility. For one thing, we're not strapping it to a sustained, violent explosion and pummeling it with supersonic winds. |
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// The one slight disadvantage is that you then have to pump the H2 back down the return line // |
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Ah, my mistake. If it's a closed loop, it should thermosyphon. |
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It does occur to me though that traveling through 16km of pipe may add a not-insignificant amount of heat via mere friction. This again makes it desirable to have your coolant lines as wide as possible (less surface area per volume). |
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Is this a global warming solution? |
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The original idea, overall, has to compare with the naturally-operating atmospheric heat-exchange systems we already use. I can, fairly easily, dump heat into the surrounding air here at ground level, and have it waft up and away--the upper-level cooling and return aren't my problems. Also, I can, if needed, push heat into water, which goes through a phase change into vapor, and some time later returns as rainwater and is piped into my building. |
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I was thinking for a while of making an insulated blimp that ascended when heated, then used its fins to radiate heat, and sank back down again. But it is all too complicated when we can just heat air or water and let nature do the rest. |
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Ah, the lazy approach. All the benefits of dilligent industry, but with no actual effort. |
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You still live with your mother, don't you ? |
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// I can, fairly easily, dump heat into the surrounding air here at ground level // [baconbrain] |
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That's true, but passively only down to the ambient temperature. If you want to go colder you have to add energy to an active system such as a compressor. The Fridge Blimp is a passive system (potentially, at least) with access to much lower ambient temps. |
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// Five miles of piping is going to lose a lot of heat. // |
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Is this even a problem? Isn't "losing heat" kind of the objective, as you correctly point out? Perhaps it is only the return (cold) line that needs insulating. |
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The main greenhouse advantage here is a zero-energy-input cooling system, not the dumping of heat into space. Sure, if you want to aim for the latter as well, insulate the up-pipe, but let's not get crazy here. |
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[BunsenHoneydew]: there must be someone with
enough money and imagination to help make this
happen! |
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My current favourite use would be as a means of
cooling ground-level atmospheric air to condense
water, thus providing a continuous passive source for
farming, drinking etc., in the various climates that
have the necessary conditions for such. The lower
structure where the base anchor, condensation heat
exchangers, plumbing, storage and control systems
are to be located, I'll call the "Oasis Tower." |
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This could be an important issue in the years ahead as
some rather large freshwater reserves run dry. The
atmosphere is only second to Antarctica in terms of
freshwater storage, so is a great place to mine! |
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I'd like to see version-1 in the following configuration
as it would be most simple to test the concept: |
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Blimp: Pressurized helium structure. |
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Tether: Two pipes, one inside the other. The outer
pipe containing hot rising hydrogen (possibly helium),
and the inner containing cold falling hydrogen. Inner
pipe constructed with ultra-low-mass aerogel walls
so as to keep the falling hydrogen cold, and to serve
as a dual wall to simplify construction. A high tensile
cable may be part of the structure, although the
tether-pipes should be engineered to be, well,
tethers and pipes. An alternate structure may be:
two aerogel pipes, running parallel to a cable, with
an appropriate heat exchanger area near the blimp,
or using the blimp surface itself to dump heat. |
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Extra lift if needed, although the tether is extremely
low mass and most likely very buoyant: helium donuts
every so often along the tether. |
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Heat exchanger: The outer pipe serves to dissipate
heat as the hydrogen moves up, and near the top
decreases in diameter to increase the surface area to
volume ratio. Advanced versions may use the blimp
to achieve ultra-low temps, as suggested. |
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Notes: Too many ideas to list, but main ones: Helium
vs Hydrogen? Support structures within pipes also
induce laminar flow. HX as part of blimp or not.
Heat accumulator on ground for improved efficiency.
Ground heating unit to improve gas lift - free AC
anyone?
Other uses list (like regenerating arctic ice on
automated ships). What is the absolute most simple
and cheap version that could be built at home?
(3000m tether). |
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An ultra high altitude version need not be made to
begin with. I think aiming for practicality, low cost
and simplicity will help, dare I say it, get the idea off
the ground. |
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Is the temperature difference at altitude due only to the drop in pressure ? |
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There's talk of using lighter than air coolant to make the up tube buoyant, thus reducing the tensile strength and support requirements. But is that really true for a vertical tube? It seems to me that over the majority of the length, the tube walls are vertical, so the gasses inside and out are not applying any lifting force on the tube except at the top. |
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I think a tapered tube that is wider at the bottom could theoretically have improved buoyancy, but I suspect that the width would get out of hand for a tube as long as the one being discussed here. |
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In any real-world system, the blimp is going to be blown sideways from the ground tether by ambient winds. So it's more likely that the up/down piping will be laying over sideways at a significant angle, say 45 degrees. I think that should be sufficiently horizontal to provide lift. |
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Eight years, two dozen annos, and nobody has yet asked for a better category choice than food:general ? |
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With so much opportunity available in the archives, now all I need to do is figure out some method to monetize this phenom (see link). |
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Regarding friction in the return line, heating the coolant: liquid helium is near enough to frictionless, if you get it cold enough. |
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