h a l f b a k e r yIt might be better to just get another gerbil.
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Steam balloon
Similar to a hot-air ballon, but with an inner gasbag filled with steam | |
A conventional hot air balloon generates lift because the density of a particular gas at a given pressure is inversely proportional to its absolute temperature (in degrees Kelvin). A helium balloon generates lift because the density of a gas at a given temerature and pressure is inversely proportional
to its molecular weight. Air has a molecular weight of about 28, while helium has a molecular weight of about 4.
Helium is unfortunately somewhat expensive and difficult to contain. At temperatures over 100C, a much cheaper gas is readily available which provides about half as much lift as helium (10 grams/mole instead of 24) but is still better than hot air at the same temperature.
My proposal would be to construct a hot air balloon in which had above the burner, a washtub-like container with a folded-up balloon filled with water. To launch the ballon, the outer gasbag would first be filled with air using a fan. Then the burner would be lit; the rapidly-expanding gas from the burner would keep the outer gasbag inflated while heating the washtub. This in turn would make the water in the tub evaporate and inflate the inner gasbag.
Since the washtub and inner gasbag would be completely contained within the outer gasbag, and since the air in a hot air balloon is typically IIRC over 500 degrees, the water would remain completely evaporated and thus have its characteristic molecular weight of 18 grams/mole.
At 20 degrees C, 100,000 moles of gas would take up about 2,400 cubic meters. Since air weighs 28 grams/mole, the air displaced by a balloon that size would weigh about 2,800kg. That would represent the theoretical maximum lift for a ballon that size.
Suppose one has a ballon that size and needs 1,400kg of lift (an "efficiency" of 50%). A conventional hot air balloon would have to heat the air up to 313C to obtain such a result. If 80% of the volume in the ballon was taken up by the inner gasbag of water vapor, however, the required temperature would be reduced: the average molecular weight of the gas in the ballon would be 20 grams/mole, and so heating the air in the balloon to 145C (294F) would suffice. Since the biggest energy requirement of either ballon once airborne would be replacing the heat lost through the outer gasbag, and since such loss is directly proportional to the thermal gradient between the inside and outside of the outer gasbag, the water-vapor balloon would require less than half the energy once airborne as the air balloon (water-vapor balloon's thermal gradient would be 125C; that of the hot-air ballon would be 293C).
The only problem I can see with the water-vapor balloon would be that evaporating the water before launch would require a rather large amount of energy. Depending upon how long the balloon would be used before re-stowing, this may or may not be a major factor.
Steam balloon experiments
http://www.flyingkettle.com/experims.htm
Steam as a "lift gas" is a given. Here is one collaborative project to achieve a working design [hollajam, Oct 21 2004]
Home steam generator
http://hbd.org/brew...y/SteInjCS1295.html
Unsure if information is extraneous regarding steam pressures. I'll post it for now. [hollajam, Oct 21 2004]
Calculating Weight of Air and Hot Air Balloon Lift
http://www.overflite.com/thermo.html
[hollajam, Oct 21 2004]
Almost same idea
Hot vapor balloon
Didn't realize when posted, has interesting followup discussion and links [pashute, May 26 2009]
Hot vapor balloon
Hot_20vapor_20balloon
[j paul, Jul 31 2011]
Coal powered water vapor balloon
[pashute, Jul 08 2013]
H2O2 Airship
[pashute, Jul 08 2013]
Thermal image of hot air balloon. Only top 3rd is actually "hot"
https://en.wikipedi.../File:Infarot_9.jpg
Hot air balloon thermal image [paamand, Dec 11 2017]
Double-enveloped balloon
http://ultramagic.c...balloons/eco-magic/
One manufacturer has made double-enveloped insulated balloons. [paamand, Dec 11 2017]
Solar balloon
https://en.wikipedi.../wiki/Solar_balloon
Solar balloons have been made with (some) success. [paamand, Dec 11 2017]
Balloon Notions
Balloon_20Notions
I had not known about this earlier steam-balloon Idea when I posted those Notions. [Vernon, Dec 13 2017]
Thermal airship on Wikipedia
https://en.m.wikipe...iki/Thermal_airship
[caspian, Oct 22 2018]
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I think you're using a redline temp a bit higher than recommended. |
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lurch: Why? What temperature is recommended? |
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So you've created a captive cloud, floating up among the clouds? |
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damn the expense, Helium's worth it :) |
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[supercat], as a former hot air balloonist I'm interested how your design works out. + |
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It would be easier using steam velocity to inflate the steam envelope initially. This would decrease some of the beneficial internal envelope pressure but steam velocity might help with the un-inflated envelope. Perhaps a boiler with pressure and velocity compounding methods would work best. High volumes of necessary distilled water would be a draw back for recreational users. |
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One major question: Is this inner steam envelope you describe an open or closed design? |
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Hot air balloons work so well because air itself is an insulator, protecting the inner mass from the cold of the balloon envelope. Sounds to me as though a steam balloon would be prone to catastrophic collapse in the chilly upper atmostphere, as vapor next to the envelope condensed. |
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Skip the washtub contraption -- it's inefficient and silly. Connect the inner bag to an ordinary, earthbound steam boiler at the launch site to fill it up, at the same time you're heating the air in the outer envelope. When you're ready to launch, disconnect the steam hose, seal off the inner bag, and go. That way you don't use any portable fuel. Maybe several balloonists can share the same boiler. |
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[UnaBubba] and [DrCurry]: Re-read the idea. The point is that the hot-air outer envelope keeps the steam from condensing, using the burner already present in an ordinary hot air balloon. As long as the outer air stays above 100C there will be no condensation. |
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The folks at the link [hollajam] posted are trying to use an insulating jacket; I think this idea is more intriguing, since it ought to be strictly better than an ordinary hot-air balloon. The only downside is the weight and complexity of the inner steam balloon. |
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Everything I can find is showing "redline" temperatures of about 250F for nylon and 300F for polyester. Those aren't operating temps; those are temps at which you are risking sudden failure of the envelope. At temperatures below this, you still have issues of gradually decreasing fabric strength and increased porosity. Polyester is claimed to have better resistance to acid condensation than nylon. |
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I'm not saying that this problem is a terminal one for your idea - just that the materials would likely need to be adjusted as well. |
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Is 100C too hot? What temperature do hot air balloons normally run at? |
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hollajam: The idea would be for a closed steam envelope within an open hot-air envelope. The inner envelope would not have to contain a pressure nor thermal gradient, but it would have to be able to support a significant portion of the weight of balloon and cargo. |
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lurch: I thought balloons operated closer to 2x ambient temperature. If they are limitted to temperatures below that (but still safely above 100C) that would seem to be another factor in favor of the hot-water ballon, since at a gas temperature of 120C (248F) and 20C ambient, a cubic meter of inside air would occupy 32.2L/mole, and thus weigh 0.87g/L, or 0.87kg/m3. The outside air would occupy 22.4L/mole, and thus weigh 1.16g/L or 1.16kg/m3. Net lift would thus be 0.29g/l or 0.29kg/m3. If 80% of the gasbag were filled with water vapor at 120C, it would still occupy 32.2L/mole, but only weigh 0.62 g/L or 0.62kg/L. Net lift would thus be 0.54g/L or 0.54kg/m3--nearly double that of a conventional hot-air balloon. |
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Although the water-vapor ballon should work adequately at such temperatures, one hazard with such a design would be that lift would fall of precipitously if the temperature fell below 100C. Designing the balloon for somewhat higher temperatures (e.g. 150C) would give the balloonist a bit wider range of temperatures to play with. |
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That's not a major hazard. In fact it may be safer than a regular hot-air balloon in that respect. Any condensation will generate a *lot* of heat; it will take a long time for the water vapor to condense -- much longer, I think, than it would take hot air to cool to ambient temperature. |
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In other words, the temperature will not fall below 100C easily; it will stay there a long time, the same way melting ice (or freezing water) stays at 0C a long time despite substantial heat input (loss). It's all that phase transition energy which you pumped in at the beginning helping you out. |
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egnor: Hmm... you've got a point there. Actually, I wonder if it might be optimal to have the air in the outer jacket just slightly below 100C. In this way, cutting off the heat output from the burner would cause the water to condense slowly, reducing lift; turning on the burner would cause more water to boil, increasing lift. Alternatively, what's the vapor pressure of water at 100.1C? Would it be practical to have a condensing tank at the bottom of the ballon into which one could pump the water vapor to reduce lift, and from which one could pump water vapor to re-increase it? |
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I think the math you want to do is calculating lift loss per calorie lost, and compare that way. That should tell if the condensation / heat of vaporization issue is in your favor or not. |
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//I think the math you want to do is calculating lift loss per calorie lost, and compare that way. That should tell if the condensation / heat of vaporization issue is in your favor or not.// |
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For long flights, the issue would be one of lift per unit power, not calorie (since heat loss would be ongoing). Since the water-vapor balloon could generate more lift at any temperature over 212F than a normal hot air balloon, and since the added weight to contain the water should be pretty minimal, it would seem that the steam balloon should have a better "ongoing" efficiency. |
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The biggest question in my mind would be whether the savings in 'ongoing' energy usage would be wiped out by the large investment in energy required to vaporize the water to start with. Since this would depend upon quite a variety of factors (including the heat loss in the balloon, the potential ability to recover some energy from the steam afterward, amount of time airborne, etc.) I really don't know how the overal net efficiency of the steam balloon would compare for a typical-length flight. |
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[supercat], operable envelope temperatures range between 70 -100 c but less so during flights in high humidity. Then the temperature is necessarily higher. |
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A typical one and one half hour to two hour balloon flight with passengers uses roughly three 10 -15 gal tanks of propane, considering all the variables |
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A standard used two-burner system appears to be running about $2,000-3,000 (US dollars). An entirely new hot air balloon system; tanks, dual burner, gondola, envelope, etc. runs $30,000 to 40,000. I feel there is a good possibility to recover the expenditure of a steam gas generator. |
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On another item, an average size four-passenger balloon has enough envelope for "sail" to keep its terminal velocity between 800 to 1200 ft/min, about 10 miles/hr if I recall correctly. And that's assuming the envelope remains in its full shape - nothing more than a standard burner failure. Only if you reduce the envelope's size made allowable by steam displacement design would you need to be concerned with potential terminal velocities. If I read correctly, it is possible to reduced the envelope size by half to get the same lift with steam gas. That's a trade to be considered. |
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It has just occurred to me that varying the hot air temperature may not be an option since the envelope must remain pressured. If there is much slack in fabric, stability can be affected. Although balloons fly with the wind, there are still shears of wind to reckon with and it is always a concern when the envelope catches the wind and begins to spin and tilt. |
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This led me to wonder if it were feasible to design the standard envelope with a donut shaped tubular "girdle" or "crown" that is used as the steam envelope rather than a balloon within a balloon. |
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The crown of a balloon's envelope consists of a circle of fabric stitched to the sides along a third of its circumference, the remaining edge presses up against the underneath edge of the sides overlapping it from above, with a little help from Velcro. A cable attached to the crown allows it to be pulled downward in desirable amounts to control for slow or rapid deflation depending on need. Heh. I've felt them all... |
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I have a link that _may_ be helpful but I haven't sorted completely through it. I'm keeping my eyes open. |
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[supercat], it's not necessarily a problem if the energy pumped in at the beginning is a lot. It's easy to get energy down on the ground, but energy up in the air requires you to bring tanks of fuel. If you could get a longer flight with fewer tanks of fuel, that would be a win, even if you have to connect yourself to a steam boiler on the ground for a while. |
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[Waugsqueke], Ballooning was my mother's business when I was in high school and college. She parted with flying after we suffered a ballooning accident. Despite standard procedures for high wind landings we were still drug into undetected service power lines by the deflated envelope caught in the wind. |
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My mother was a contemporary aviatrix with a career in Air Traffic Control before retiring so I grew up in control towers and at air shows, air races, and 99's meetings - quite saturated in aviation. I didn't miss her departure from aviation in the least ... back then. I do miss the association now, especially the ballooning. I just have a different momentum going that prevents me from taking up the sport again on my own. |
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Thank you for asking, waugs. |
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You can add a steam engine w/propeller. the exhaust would replenish any loss heat/steam. Very Jules Verne. |
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Croissant for you - indeed, foranything that helps reduce the demand for the world's ever-dwindling supply of helium, thus freeing it up for making our voices all squeaky. |
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Why not burn hydrogen to fill the balloon? Probably a simpler way to get superheated steam. |
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Yes, Dr_who, instead of pressureized tanks, it can be stored in additional gas bags to add lift. |
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Instead of hauling around a large steam generator, I suggest using the magnetron from a microwave oven. The beams of microwaves could bounce along the edges of the aluminized envelope heating the water gas. |
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I like the microwave idea, energy for the microwave could even be renewed "on the fly" by a wind turbine suspended from the balloon, this turbine could also double as a propellor, driven by the current stored in a small fuel cell. |
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Instead of storing hot air in the outer envelope to keep the steam in the inner envelope from condensing It might be worth investigating to fill the outer envelope with small aerogel marbles for insulation , perhaps this layer of aerogel granulate could double as a hypercapacitor to store a vast amount of electric energy wich would save weight by making a fuel cell redundant... |
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Unless the balloon is tethered to the ground, the speed of the balloon will match the speed of the wind within minutes of the balloon's launch. |
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Thus, putting a wind turbine on a balloon would be rather pointless. |
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A better solution might be to coat the outer balloon with a thin film of photovoltaic material, layered on top of a thin film of thermoelectric material (which would pump atmospheric heat into the balloon). |
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A thermoelectric coating applied to the inner balloon could be used to pump heat from the hot air into the hot steam, if it's desired that the steam be hotter than the surrounding air. |
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I know that thermoelectric heat pumps are not very efficient, and produce more heat than they do cooling, but since heat is what we're after, it's no less efficient than electrical resistance. |
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I think this idea would work as is, but if the temperature is
too hot for the materials a compromise is possible. At
temperatures not too far below 100 C you can still use
steam if it's mixed with air or nitrogen - in a sense this is
just humid air, just hotter and less air than normal. I think
I read water at 80 C has nearly half the vapour pressure as
at 100, so a nearly equal mix by volume would work. |
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What is the internal pressure of a balloon? It has to be slightly greater than atmospheric at current altitude, or it would collapse under any breeze. That being the case, how much above 100C is the actual boiling point inside the envelope at launch? (Point of maximum atmospheric pressure) |
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the internal pressure of a balloon has to be atmospheric at current altitude, because there is a big hole in the bottom of it. |
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The vapour pressure of water
40 c 55.29 mmHg
60 c 149.4 mmHg
80 c 355.2 mmHg
90 c 525.9 mmHg
98 c 707.3 mmHg
100 c 760 mmHg
102 c 815.9 mmHg. |
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I like the double skin idea.
if you are thinking of mixing steam and air then there is a good idea called a water vapour balloon elsewhere on the HB. |
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Do you have a link to the water vapour balloon idea?
[pashute]'s one doesn't mention including air and I didn't
find it with a search. |
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//What is the internal pressure of a balloon?// At the level of the opening, the internal pressure is equal to the external pressure, but higher up in the balloon the internal pressure is greater than the external pressure; this is because the pressure gradient in the atmosphere is steeper than that in the less dense gas in the balloon. |
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However, nowhere inside the balloon is the pressure greater than that of the atmosphere at the neck. |
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Sorry that should have been a hot vapor balloon |
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Hot air balloon pilot here. I really like this idea. In the simplest form
we could simply add an atomizer at the burner that would add as
much humidity to the air as possible - e.g. 50% at 80C (normal
operating temperature).
I am thinking about how much extra heat-loss you would have
without further modifications of the current envelope? Current heat
loss is in great part due to permeability of the fabric. Less
permeable fabrics become heavy. But with less required volume
comes less surface area. |
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Comments on a few suggestions in the thread: Insulating double-
envelopes has been done (link added)
Pressure in the balloon: Same at the bottom (it's open) but higher at
the top, since the /gradient/ is lower due to the air being lighter. No
need to pressurize to keep shape. Pressurized envelopes has been
done for thermal airships. Impractical due to permeabililty of fabric.
Operating temperature: Normally around 80-100C (depending on
load). Above 125C is redline for typical nylon-based fabrics. |
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Only the top 3rd part of the balloon is "hot". See link added. |
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Other thoughts: Ammonia has been used as a lifting gas. A
water/ammonia mixture could be considered.
Solar balloons has been made: (link added) |
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Welcome to the Halfbakery, [paamand] ! |
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I look forward to your floating some ideas .... |
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On the contrary; nature is very trying indeed. |
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I hadn't heard of thermal airships, what a neat idea. The wikipedia
page even mentions using steam. |
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If you do use steam or humidity, you don't want to have to replace
it using stored water, because any spare liquid water you bring
will take quite a bit of weight (about as much weight as the
buoyancy it will provide, since the gas is about half as dense as
air). |
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I'd also wondered if it is worth trying to keep CO2 from the flames
out of the balloon, since it is heavier. |
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