Lightweight Containment of Helium

Sounds like a plan, but also keep in mind that the nitrogen (N₂) molecules won't actually plug the 'holes' in the mylar. At temperatures above ~77.5°K (the boiling point of nitrogen), the nitrogen molecules are continually in motion (true even in liquid form). They'll collide with the mylar constantly but won't stay put. Meanwhile, the helium atoms will leak through the mylar at every opportunity. Even when smacked head-on by a nitrogen molecule, the helium might retreat back into the mylar, only to emerge again soon afterward. Helium atoms are very persistent little buggers; so much so that there is no material known to Man which will contain helium for very long. Helium atoms are tiny (even for atoms) and they're completely inert. They don't form molecules and they don't interact with (ie 'stick' to) their surroundings. To a helium atom, everything we call 'solid' is just so much swiss cheese. Pressure on the 'other side' doesn't discourage leakage all that much because even at very high pressures, the probability for some gas molecule to collide with the helium atom just as it emerges from the barrier is very low. The probability of this happening time and time again to keep the helium atom at bay is minute at best. And so after awhile you'll have a nice mix of helium and nitrogen - and no lift. Wait a little longer and all the helium will escape the entire contraption.

Nice idea, at any rate.

-e

Excellent reply. Thank you. exactly what I was looking for.

With the Mylar, it is metallized on one side, so it at least slows down the helium. If a metal cylinder can contain it completely, like a regular 58L gas bottle, what do you think the minimum thickness of metal would be to significantly slow the migration? (like an aerosol can wall thickness?)

thanks again.

Chris

The helium will completely diffuse through the walls of the gas bottle, given sufficient time. My first guess is that the total diffusion time is a function of wall thickness, container volume, differential pressure, and wall area. The metal used to make aerosol cans may also have microscopic structural variations that also may affect diffusion rates. Aerosol cans are typically made from rolled steel sheet which has an extensive and pronounced grain. I'm not sure about gas bottles, though. As metals are seldom (if ever) amorphous, crystal structure may play a part in the rate as well, though to what degree I'm not sure.

-e

Rather than trying to reduce the diffusion rate as a first step, just let the helium diffuse and provide the means to replenish it on an as-needed basis. Then focus your energies on your "aerocycle" design, itself, and get it 'off the ground' so to speak. Work out the containment details and, when you've had enough hair-pulling for one day, take your machine for a spin to 'decompress.' That way you can have your cake and eat it too - in flight!

-e

My first encounter with the problems of helium containment happened in high school. I built a helium-neon laser which worked just fine for a year or two, but after that it stopped lasing. I replaced the tube with another of a different design and it, too, failed after a few years. Turns out in both cases the helium had diffused through the glass leaving only the neon and a trace amount of helium behind. Here is an example of how helium can diffuse through a supposedly 'dense' barrier to a much-higher-pressure environment. The gas pressure inside an He-Ne laser tube is very low, yet the He was able to diffuse completely through the glass to a side exposed to normal atmospheric pressure. It took a while, but eventually most of the helium evacuated.

-e

The old zeppelins used hydrogen, which is a smaller molecule than helium - what did they use?

The hydrogen is actually h2 and so is larger than the helium.

here is an extract from a Hindenburg examination:

"the substance used to coat

the cotton skin was extremely flammable. A

combination of iron oxide, cellulose acetate

and aluminum powder "the total mixture might

well serve as a respectable rocket propellant,"

hmmmm.

chris

SOUNDS like the stuff we would all like to use

best way to hold in helium is to metallize mylar. It is better than mylar alone. In larger structures they can afford the weight of thicker containment methods of denser stuff. In small structures the metallized mylar you see it the only way.

I had a thought that a 1/2" layer of fine cell foam would have some effect and also be light.

I bet there is a body of work on this.

http://spot.colorado.edu/~dziadeck/airship.html

We had the same stuff in our latrines when I was in the military. Except it came on rolls.

You didn't dare throw a lit cigarette in the can after using the stuff.

-e

actually, i feel funny saying this but on the discovery planet mith-busters show they tested the theroy that the paint was responsable for the burning but the conclusion was the over all the paint had no effect

Christo, Great line of thought. Always put personal safety first.

The history of containing inert supposedly harmless helium with a second pressurized gas has ended in the untimely death of unaware employees. Given a short time, helium at any pressure leaks through any container material known to mankind. Rather than combine with the second retaining gas, inert helium simply passes on through the blanket gas and exits through the second retaining container, no matter the retaining material or the blanket type gas.

Puzzled management sends unsuspecting workers to check on the sudden and unexplained "loss in pressure" through a double container of whatever exotic material. Upon arrival at the scene with triple escort for safety backup, the lead party suddenly crumples over as if "out of oxygen". The second lead kicks the first in the rear, admonishes the simplistic slumping jest, and proceeds to rescue the "fake". Luckily and wisely, the third party retreats for help when the second slumps uncontrollably. Upon return with backup and slowly proceeding with caution, all highly trained rescue members can do nothing but evacuate the helium prior to retrieval of two dead bodies.

Totally inert and harmless helium displaces oxygen, a life sustaining requirement for humans. In the absence of oxygen, humans can not survive.

Thanks again for requesting advise prior to trying this at home. And pleeeese, do not try to blanket contain helium with another gas or any material known to humans. The concept has been tried by some very large companies with brilliant employees, sponsored by NASA, attempted by Power Companies, but the innocent employees paid the untimely and ultimate price because of failure or too much pride to do what you just did, simply ask for free advise.

You wrote: "The concept has been tried by some very large companies with brilliant employees, sponsored by NASA, attempted by Power Companies, but the innocent employees paid the untimely and ultimate price..."

It would seem here that not one of the many people involved had any experience or insight into the problems of helium containment by any method whatsoever - including having any experience with toy helium balloons which always go flat after a few days and wondering why? Nor, apparently, were small-scale laboratory prototypes first constructed to test the containment method before committing money and manpower to a larger version. Somehow this seems inconceivable.

-e

Industrial myth, I think. The results for any particular structure are just too easy to predict. Plus, the standard approach to problem analysis would involve a gas sample without requiring anyone to enter the area. And then it takes a while for oxygen stored in the blood to become that depleted, so the first entrant would not simply slump. etc. etc.

Seems like the idea won't "fly" anyway, but, there's a fundamental flaw: if the N₂ is at a higher pressure the inner "balloon" will simply collapse until the pressure equalizes.

Be careful: not sure if it was an urban legend, but, wasn't there an early Darwin award to some guy flying over the pacific in a deck chair held up by Helium weather balloons.

Seems to me that even if one did not anticipate the inner balloon collapsing and built the contraption anyway, he/she'd find this out soon enough and use a rigid inner 'balloon' on the second pass. Not really a 'fundamental' flaw, as such, just one that can be avoided simply enough. The study of airship design wouldn't hurt here either.

I just wonder what the cyclist is going to do in a stiff breeze! I can just see it now "...the airship Enterprise...It's five year mission...to go where no one has gone before!" (start theme here)

-e

If you could make a balloon rigid for a lower internal relative pressure you'd be home and dry as far as the original question was concerned: the air is 78% nitrogen and most of the rest is pretty similar "mechanically".

However maybe we can salvage something from this, and, perhaps this was part of Chris' original plan. If you make the envelope thin and connect the inner and outer surfaces with webbing: how much of a vacuum can you sustain in the inner balloon. This will clearly depend on the pressure (and more pressure more density unfortunately) of the gas in the envelope: is there an optimum envelope thickness/pressure.

If the object of the Hydrogen cocoon is for optimized or more persistent buoyancy, I'm having difficulty seeing it. In simple, qualitative terms, here's why.

Correct me if I'm wrong but...seems that the He permeation rate would be a function of pressure, and of ascent/rate of ascent; thus, the toy helium balloons lose boyancy (and maximum attainable altitude) as they rise--which is a good thing for safety purposes--and before attaining neutral buoyancy...or "nominal" He depletion.

If the Helium bladder were cocooned with hydrogen...seems that this would further increase the internal pressure of the greater quantity of He...thereby actually increasing He permeation rate...until the gasses reached equilibrium...at which point He permeation of the cocoon itself would commence...possibly just as quickly (from launch), because the added hydrogen would increase initial "system" buoyancy. Am I making any sense?

Oops, I meant to say, Nitrogen. But, same principal?

The helium will diffuse across the membrane due to the difference in helium concentration. It makes no difference what the pressure of nitrogen is on the outside. It's the same reason that pressurizing a carbonated beverage with compressed air will not keep it from going flat.

I looked at metalized mylar under a microscope when I was trying to find a moisture impermeable coating for a lithium battery application. It looks like the night sky full of stars; pinholes invisible to the naked eye, but wide open spaces to a helium atom. I think the most impermeable material for your application is solid metal. Gold leaf is available very thin and might do a good job without too much of a weight penalty. However, filling up a common balloon before each flight would probably keep you up for as long as you want to pedal. I'd be more worried about the hazards of being carried away by the wind.

The reality is that the pinholes are not the main problem. It's the 'holes' between the atoms in whatever coating you choose to use, whether it has pinholes or not. Whereas the pinholes are scattered at random (and are pinholes in the coating only and not in the mylar itself), the 'holes' in the atomic lattice pervade the entire surface. It is through these 'holes' that the bulk of the helium escapes.

-e

Dude, you can't prove that.

I have to disagree. For one thing, there is increased resistance due to friction against a surface, right? If you have a hole and chop it up into tinier holes, you will slow down the rate at which a fluid can pass through it. That's because you are creating more surface area along the escape route.

Putting a coating on a surface will make a considerable difference. Filling those pinholes will make a considerable differece. Who can say how much without experiementation, but physics can tell you - more friction, less leakage over time.

Assuming a coating that was correctly applied (this is likely because the pinholes are invisible to the naked eye), Europium will be correct. In the end it's a compromise, because the coating is made as light as practical to minimise the size of the envelope (and the helium load) that is required. If we thicken the coating the diffusion through the material per unit area (and through any holes) will reduce; but if we go beyond the optimum thickness the area of the balloon will need to be increased disproportionately - so the total losses will increase.

Your question suggests an interesting problem. Given that helium diffuses through any known barrier, try this experiment: Fill a rigid, hermetically-sealed container exclusively with helium. Any pressure is fine, although the lower the initial pressure the less time this experiment will take. The container pressure is measured by a suitable gauge (or gauges) which can measure pressure/vacuum all the way down to 0.0 fT (low enough for gov't work). Now, leave the container on the lab bench and do something productive for a couple of eons. Will the container eventually contain a near-perfect vacuum at the end of a suitably long interval? It should, I think.

Any takers?

-e

"No" - -Thermodynamics

Misleading oversimplification! Eventually, it would have the same content as if the helium had not been there in the first instance.

However, if you time it right (and the window is quite large), the helium content will be almost the same as that in the earth's atmosphere (rather small), and almost no other gas will heve diffused in. It's equivalent to the osmosis experiments we did in high-school.

That's my guess too: the equilibrium condition of having the same density of He inside as outside. But given that europium said "near perfect," and not "perfect," I'd say his hypothesis was correct, wouldn't you say, given the density of He in the atmosphere at ground level? At any rate, your reply was certainly more informative than the previous poster's abrupt "No! -- Thermodynamics." Who needs that kind of answer?

ChrisG asked a relevant question that was not answered - what is the relationship between wall thickness and diffusion time? For a given container material and helium pressure, the rate of diffusion should be roughly inversely proportional to wall thickness (the concentration gradient throught the container reduces as the required diffusion distance increases). That is why gas cylinders can retain helium for extended periods. Ignoring other loads, you would of course need twice the depth of helium to support twice the wall thickness. So the viability depends on how you long need the balloon to last, and how large a ballon can you cope with (something like the cube of the helium volume?). Conceptually, keeping a top-up supply in a second cylinder as ChrisG also suggested sounds useful as well. However, I fear the entire enterprise would be taking extreme sports to suicidal extremes.

OK, I'm going back to the original "human powered - helium filled aircraft" topic. How about hot air instead of helium? And instead of the conventional hot-air baloon, lets say a chemical reaction between two or three substances (hopefully lightweight) inside the enclosed envelope:

Lithium is light weight and highly reactive. Can give lots of heat per pound.

What does lithium react with?

If left out on a table it will burst into flames from reacting with water molecules in the air, unless it is in a dry room. A controlled reaction could be obtained with regulated amounts of sulfer hexafluoride.

Thanks. I always thought lithium was a salt. Is this incorrect? (I don't know too much about chemistry so I wont even ask about sulfer hexafluoride..) I was just thinking about ways of producing heat. Is the by-product toxic or caustic? I wouldn't want to breath it...

I rather think that mycoman's Lithium suggestion was meant to be facetious. Lithium will react with nearly any oxidant. The most readily available oxidant for use in a balloon would be oxygen itself, which I wouldn't really recommend, because LiO2 is a rather corrosive alkali. Lithium fluoride and lithium chloride are themselves relatively safe, but it would be hard to control the process so that no uncombined chlorine, fluorine, or lithium is released.

Fyz

Thanks. I guess I'll stick to things that I know about, and not mess around with any of this

Perhaps I was being a bit facetious, however our military does have a weapon system that uses lithium combined with sulfer hexafluoride to generate heat to produce steam to run a propulsion turbine. I wouldn't seriously recommend it though unless your are Uncle Sam. This propulsion system could be more dangerous than the warhead it is intended to deliver.

That might be fine as a rocket propellant, but I wouldn't fancy it in a balloon, where the "exhaust products" can fall straight onto you...

Fyz

One thing I'd look into is the CRC manual for lightweight reaction products - provided they themselves are not hazardous. Or you could generate hyrogen by electrolysis of water. You'd need to carry water, of course, but your electrical power might come from lightweight solar cells. After an initial charge of hydrogen to inflate the craft, the electrolysis might serve simply to maintain the supply. The Hindenburg debacle doesn't serve up many warm fuzzies in favor of this gas, of course. Perhaps today's technology could mitigate the safety problems of using hydrogen. (and as oxygen is the other product of water electrolysis, for high-altitude cruises it could supplement your supply.) Just brainstorming.

Here is a concept idea... use counterrotating propellers in pusher configuration, with steerable tail. use many shaped membrane cylinders (like airmattress) inside the basic shape, to contain gas, with a complete skin on outside. therefore a single cylinder failure is not catastrophic. use gyros for yaw control (human powered again)

no need for hard material pilot furniture.. just like sitting on an air chair. It would have to have a supplemental weighting system for when the craft doesn't have a pilot in it. adjust ballast to tune for weight of pilot...etc etc. make the volume of the craft large enough in lift coefficient of gas to offset dead weight. etc. like a big guppie.

most heat comes from combustion, preferably into gasses you can vent and also preferably from stuff you do not need to carry.

It would be nice to draw air and methane from the atmosphere, combust them for heat and then vent them.

We can do most of that. Just carry the hydrocarbon fuel and use air to butn it and vetn the spent gasses.

As for weight carrying, 1000 cubic feet of air weigh about 60 pounds, so 1000 pounds of vacuum will have that lift potential(less the weight of the vacuum box). So we use helium with ~90% of that lift capacity and the whole weighs 240 pounds (if we can make it that light).

Now a sail that is 16 feet x 16 feet feels 2.3 pounds per square foot of force in a 30 MPH wind = 220 pounds. SUch a craft is hard for 1 man to manage and drag is a square function.

60 mph wind and the force is 4 times much = 960 pounds = no fun if it is your day job

A 180 pound man and a plane that weighs 60 pounds = 240 pounds /54 = 4,400 cubic feet of Helium. That is a ~16 foot cubed structure

So a 180 pound mand

That's really excellent information. thank you.

I don't think that a human powered aircraft should be flown on windy days. My parents used to rent a cottage on an island just below the Chats Falls on the Ottawa river.. and every once in a while somebody in a canoe would decide that they didn't really have to heed the alarms of the impending spill gate opening. (daily) and we would then have to go rescue them in a power boat. A canoe in the tailrace of a dam is a bit like whitewater rafting... not so good.

I can only see such an aircraft being a leisure vehicle, just like a hot air balloon. It would in fact be much more steerable than a hot air ballon... the propellers, steerable tail, and gyros give a fair amount of control.

I was also thinking that it would have to be open cockpit style, based on Europium's discussion of Helium's ability to displace oxygen. I think it would be used within 500ft of the ground, and given it has a slightly negative lift, if it becomes unpowered, it will have a slow glide to the ground. If it has a tough hide exterior like TEDLAR then it could even survive a run-in with trees, wires, buildings etc. and be patchable. On the heating side, while you could even use solar absorption (transparent on top, black on bottom) you would have to have a way of adjusting your lift ratio, or you may have difficulty returning to ground level.

Chris

Chris, I don't know how to put this to you tactfully, so I'll just speak plainly: there are easier - and cheaper - ways to escape from Alberta.

hee hee... that's funny... especially since I escaped Ontario and drove out here just over a year ago! but I do want to see the world...

Fun thought. I particularly like the air mattress gas bladder concept.

There was an inflatable plane.

Been awhile since I looked at it.

I found your post because I have a similar question, although mine does not involve flying and therefore weight is not an issue. Helium has good specific heat capacity, and I'd like to use it to maintain temperatures in situations where water alone could freeze, and water with antifreeze loses the heat capacity. Hydrogen would be a great choice if I didn't mind my house blowing up, but I do. Helium would be great *IF* I could contain it. Since weight is not an issue, are there containment systems that I could use? Even if I have to replenish it every year or two?

helium loss is only a problem with very thin containment methods, as in balloons, where you use 1 mil films or less.

In sealed containers of sheet metal you can contain it for millennia. It does diffuse faster through plastic containers.

Where can I find information on the diffusion rate through thicker films or other materials?

Chris

A university library will give you access to this.

http://links.jstor.org/sici?sici=0080-4630%2819350501%29150%3A869%3C172%3ATDOGTM%3E2.0.CO%3B2-A&size=LARGE

a simple search givs this.

change to plastic etc to modify it

http://www.google.ca/search?q=%22rate+of+diffusion%22+%2Bhelium+%2Bmetal&hl=en&lr=&start=10&sa=N

Figures 8 10 and 13 of http://www.osti.gov/bridge/servlets/purl/10104713-z0DbGL/native/10104713.pdf give permeation rates through some Mylar films - and one of Aluminised Mylar films. Note the temperature dependence.

High (mass) specific heat capacity is all very well, but (at atmospheric pressure) the volume specific heat of helium gas is only about 1/5000 that of water. In this respect, non-ideal gases (such as N2) are slightly better - but still pretty awful.

So, if you wish to use a gas, you will need either high pressure or large volume (or a combination of the two). Of course, large volume tends to mean large surface area, which makes insulation difficult.

I believe that the volume specific heat of the optimum low-temperature ethylene-glycol-water mix is about 83% of water. Even on a mass-to-mass basis that represents about 60% the specific heat of helium.

If weight really isn't an issue, I'd be inclined to stick with water+antifreeze. If there is another issue, such as concern about the possibility of leaking solution, concrete still does quite well...

N.B. Apologies for placement - this was intended to reply to post#36

Thanks -

Concrete is no good - it needs to be fluid (in the moveable sense, so gas is fine). I hadn't thought enough about the mass though...

I'm only guessing at the constraints - so: would a rigid enclosure spaced from your sample by dry air be suitable? Placing insulation around such an enclosure would be relatively straightforward.

Yes. Here's what I want to do - we have 2 heat pumps, very inefficient at extreme temps (both high and low). We looked into switching over to geothermal heat pumps, but the cost of drilling half a dozen deep wells is prohibitive. What makes the heat pumps inefficient is the temperature differential between what we want inside and what is ambient around the heat pumps. So now we're thinking that instead of heating the whole house geothermally, we can heat the space around the heat pumps geothermally - one (closed loop) or 2 (open loop) wells should be fine for that - to reduce that temperature differential and increase efficiency.

So we're thinking about building a vented shed - perhaps brick as an external thermal mass, housing a series of radiators pumping the geo-temp substance, surrounding the heat pumps. If it's water alone, we can do it open loop with shallow wells, otherwise it has to be closed loop, and probably a deep well. The idea is young, details to work out. It's possible, maybe even probable, that H2O + antifreeze will do the trick. But I had to ask.

You might be able to use the ground as a long-term heat averager simply by burying pipes about 1-metre below the surface. Assuming that you have the space available, the ground is a relatively cheap source of thermal capacity, and (other than loss in heating efficency) you don't really care if the ground freezes - so long as the fluid in the pipes does not. Viability depends the average temperatures where you live, and local soil-types. The only issue is that, if your location is not suited to this (or whatever) arrangement, the energy footprint of the installation can easily exceed any reasonable recovery time.

Ok, a geothermal heat pump works fine as long as you can draw ~50° F water to it.

How far North are you?

Most people use trenches with cross drills for geothermal sources.

You can also use deep drilled wells in clay cheaply. In rock it costs extra.

You dig two trenches 30 feet apart about 6 feet deep and 40 feet long. Then holes are drilled , near the bottom, from one trench to the other every 18" and a 2" plastic pipe is run between the trenches. This will give you 1200 square feet of area 6 feet down to use a geathermal heat sink.

Some links here.

http://www1.eere.energy.gov/femp/pdfs/hyhgp_tir.pdf

more here

http://www.google.ca/search?hl=en&q=%22geothermal+heat+source%22+%2Barea&btnG=Google+Search&meta=

We're on Kent Island in the Chesapeake Bay. Actually, the bay serves as a wonderful heat sink in and of itself - we're generally 10 degrees warmer/cooler in the winter/summer than inland! But always looking for better....especially in the worst months. But the water table is high. Digging a 40 ft trench at 6 ft deep might mean digging a river. Still I appreciate all ideas! I seem to have derailed the topic from helium containment. Sorry!

well, all you need is a plastic piped heat exchanger for summer/winter use. In that area you need minimal protection for the piping. Depends on your access to the beach front? With access the use of the water is easy. with no access you would need to make a surface heat sink in the back yard of some kind, but that close to a water table, if the island is gravel you could draw water from one place and inject it back 50 feet away?

That may be what we'll end up doing (draw and inject - we don't have access to the beach). It does freeze here sometimes, not for 3 months like up north, but a few times each year.

I've been thinking along the same lines, of a bicycle powered flying wing of sorts. But even if you don't contain the helium, you can replace it, as in airships. The problem with the flying bicycle that I see is control over the aircraft. You need 4000 ft^3 of volume to contain the He just to become weightless. That accounts for about 180 lb person with 70 lbs of machine and material, which would be extremely difficult to manage. Putting this kind of volume into a wing of 1ft thick would create a 64' x 64' area of wing. I don't believe that your diagram would fit that kind of volume. But even adjusting for size, the surface area would create a lot of air resistance, and any breeze would blow it away, literally. I just don't know if a fan, powered by a cyclist can generate enough force to control it.

Have you made any progress?

Tim

Did you follow this thread:-

http://cr4.globalspec.com/thread/16735/Vacuum-chamber-walls-in-tension

In particular the reference and link in post #18 to:

Stability Analysis of an Inflatable Vacuum Chamber.

http://arxiv.org/abs/physics/0610222v4

Which, can apparently be made buoyant in air.

Hi Chris. I read your comments regarding helium containment. I have also had ideas about a helium based flying machine and am wondering if you have made any advances regarding containment yet. Chris

chrish99@shaw.ca

no further ideas or experiments on this one.

sorry.

Anybody know what has happened with Windream one? I checked www.rousson.org, but can't seem to get anything current. They had a good prototype flying.

hmmm, i'm not sceince expert, i'm not even sure how to spell science right, but i am extremely interested in the idea of containing helium to give an object boyancy. I was wondering if u could have uncompressed helium in some kinda of like, sack and put it a layer of oil (vegetable) or something that is pressurized and air tight. Would the helium bond with the oil, idk, and also idk if the heliums effect would be overridden by the weight of the oil.

Been watching this thread for a while. Chrisg, you have to get your eye on the ball. Losing some helium is just part of the game. You don't see other blimp users worrying about helium loss. You just replace it when you land. Carry ballast to compensate for the loss.

Concentrate on ship design. The inflated airplane has been done, works. Think lifting body, the Space Shuttle is a good one, the engineering has already been done for you. You have to decide what material you want to use. Check my avatar. That ship (ZMC 2)was aluminum, no inside bags. They sealed the seams. It flew for years. Filling must have been a chore! Personally, I'm looking into plastic.

If you really want to get wild and crazy, go to hydrogen. With solar panels and the new generation technology, you can make more in flight out of rain water. You have to plan for a speedy escape if the damn thing blows up, of course. Learn base jumping, wear nomex. I plan to use solar electricity for the motor, anyway.

P.S. The Hindenburg had gasbags made of cow gut, apparently good stuff. It keeps gas from migrating out of intestines into the body cavity, must be tight. The skin of the Hindenburg played no part in keeping the gas inside, it protected the insides from the weather.

Do you know if or how to expand the size of individual helium molecules? Does helium become less buoyant as temperatures affecting it decrease?

Chrish99

Oh, boy, you guys really have to start watching the Science Channel or something. Basic gas laws state that as gasses heat, the molecules move more rapidly and the area they occupy expand. The size of the molecule is controlled by the atoms that create it. If a gas is cooled enough, it may liquefy. The liquid is, of course, more dense and heavier than the gas. In between gas and liquid will be a cold, denser gas that probably occupies less space, and therefore displaces less air, and therefore would have less lift. Hot air balloons use this principle.

On the other hand, if you warm your gas up, you will get more lift.

I wonder if ionized Helium contained with a magnetic field would help ?

So what is the difference between Hydrogen leaking and Helium leaking out of a envelope ? Given same pressures , and all . In layman's terms please. If both envelopes of the same size and material , were filled at the same time , how long would one out last the other?
This makes a huge difference in the cost of replenishing the envelope and making this affordable and doable. As Any common, quality made aerostat envelope could work. It wont have to be "special"

Hydrogen Is way safer than Gasoline in a can any day. , as long as air in not mixed with it. And even if it were , the resulting explosion (Only if ignited) would be quick and loud and in the direction of UP ! with all the fuel being burned up instantly , producing no flame spread like with gasoline explosions where it goes all over and in the direction of DOWN and ON you . Buying Pure Hydrogen from a welding supplier , would be my option over trying to make it just because of the shear volume of gas needed and the security of knowing IT IS PURE !

The difference will vary somewhat depending on the material of the envelope. However, the typical situation is that helium diffuses at about 2/3 of the rate of hydrogen.

The only way to avoid helium loss is to have a shell around your helium vessel and operate a scavenging mechanism to extract the low amount of helium in that vessel and pump it back into the inner vessel. The outer vessel will also lose part of the helium by diffusion through it's thin skin = not a foolproof plan and the weight of this mechanism has to be taken into account as it represents an added burden.

You can also use ammonia gas NH3 for lift, with a molecular weight of 17. If you heat this up to 100C it will have an effective MW of about 12-13, so it will have substantial lifting capacity and will not leak through membranes, it is a large bulky molecule, better than hot air, cheap and if it leaks you can smell it.

Wouldn't 100 ^OC would only reduce the density by about 30% at working heights - and what about the energy usage?

Methane (CH4) is slightly (6%) less dense than ammonia (NH3), and has a low boiling point, so it shouldn't need to be heated. But it would still need twice the enclosure volume as would helium. Both CH4 and NH3 are somewhat flammable, of course, so you'd need similar precautions as with Hydrogen... (Not sure about diffusion rates).

Would electrochemical replenishment of hydrogen use more or less power than maintaining a large surface area (the envelope of NH3) at 100 ^OC?

NH4 burns, very well,

CH4?

Indeed, much better than ammonia. The LEL is similar to hydrogen, and about 1/3 that of ammonia.

Given that this part of the thread started by accepting the flammability of Hydrogen, the question remains how far along that path we can make it safe to travel.

If we can't accept methane, the comparisons we have to make are between NH3, replenished hydrogen, and He. At this point I can't see how ammonia wins this one.

Have a look at the safety record of the Zeppelins when they were in service . Its impressive to say the least. Using a Thermite covered envelope was the cause . Certainly it was spectacular and media had a hand in sealing the fate , But seeing that jet cartwheel down a runway , ON FIRE ! was FAR more spectacular And 2 times the death rate of the Hindenburg. , yet we still load them up every day . Pure Hydrogen is safe , It doesn't explode , only burns when Ignited and only with air present . When Hydrogen is super pressured like on the Space Shuttle Things change , But at atmospheric pressures this personal airship would use , its safe enough. At a 2/3 better retention in envelopes, Better lift, and not being a rare expensive gas, I'm using it. Its cheap enough to vent and re supply from a on board cylinder and not worry with "producing" it in flight. Not that this Little personal airship could even carry a H gen or Cylinder. But it would be sure cheep enough to deflate and pack up in the truck when your flying day is done and not worry with trying to store it Inflated .

I'm the guest you replied to.

In general I agree with your viewpoint. Hydrogen (or any flammable gas) only remains safe while you can keep it pure - but that becomes harder (outside the envelope) as the volume increases. Of course, the safety record of hydrogen-filled airships was nowhere near modern standards, even if we exclude the Hindenburg incident. You are doubtless aware that the Thermite theory remains disputed, and that Eckener strongly advocated the use of helium following the R101 incident.

You are probably also aware if arguments favouring (on the grounds of safety) the use of gases with lower diffusivity than hydrogen (such as CH4 and NH3) for large envelopes, this in spite of their higher specific energies of combustion; personally, I'm not convinced - and in any case doubling the required volume does not look to be a sensible economic trade-off.

Given that the additional cost of using helium is not all that great, this would seem to be the way to go if one were serious.

What about a blend of Hydrogen and Helium? Would that make the mixture less combustible? (and less helium to escape?)

As we only need 15% by volume of H2 in air to form an explosive mix, even 50% H2 concentration inside the main envelope means we have to provide mechanisms to ensure dilution. I suspect that once we incur the cost and weight involved, we may as well go "the whole hog" and get the extra lift available from pure hydrogen.

The devil is (as ever) in the detail - which perhaps is why Hybrid Air Vehicles and Grumman are sticking with Helium - at least for the time being.

If pure Hydrogen gas were placed in a vacuum jar after all the air was removed, with an electrode sparker inside, like used on BBQ grills, and triggered to spark There would be no explosion, not even a fire. WHY ? because it takes AIR to make combustion . And it takes 900 something degrees AND air for Hydrogen to ignite and burn. Gas in your tank only 500 something to ignite. Hydrogen has a 2/3rd's better retention in envelopes than helium. And it cost 1/4 the the price of Helium in welding cylinders .
No, a mixture of He and H renders no benefits what so ever. Keeping a Pure gas in the envelope does matter. At the cost to refill each time you fly H is affordable and Its as safe or even safer as filling your car with gas. A weekend or maybe even a week of flying and then dump would be very safe as long as your envelope is sound. . Keeping the gas in for a long period, say months , would be risky as air will migrate in as H permeates out. Its unavoidable .
If the envelope develops a leak the pressure blowing out will keep air out and will not explode even if this leak were to catch on fire.

It would be wise to scent the hydrogen somehow.

I appreciate all this expertise.. and some hope on an idea I thought was dead 2 years ago. thank you.

What are the relative weights or buoyancy factors for Hydrogen (H2), Helium, and Nitrogen?

For my purposes, the 'lighter' gas would smaller volume requirements.

Here is a very helpful link surrounding what you want to do http://www.chem.hawaii.edu/uham/lift.html
Nitrogen has so little lift its not worth looking at . Price wise hydrogen has all the lifting gases beat.
My thoughts on a one man powered air ship was basically simple and using currently avab components. It uses a Powered paraglider cage and harness with a 23 foot Dia Parabounce or King fisher aerostat . Filled with Pure Hydrogen. The only Modification to be made would be to place a rudder and elevator in the prop wash of the PPG unit for directional control. It would be directional to a point depending on the wind , But good enough to prevent landing somewhere you don't want to . And in , no , to very light wind, you would have total control. It would be a total Hoot to fly it ! And don't forget the reserve chute !

Man still wants to fly. And so do I ..

"Keeping the gas in for a long period, say months , would be risky as air will migrate in as H permeates out."

I agree this part of your conclusion, but the way it is written suggests a relationship between the outwards diffusion of hydrogen and the inwards diffusion of air. Any such relationship would of course be negligible.

Regarding the comparison between safety of H2 versus gasoline in your fuel tank, I'm not so sure. There is little argument that gasoline storage is intrinsically more dangerous than storage of unpressurised hydrogen; however, this is by no means the same as comparing a proven system for storage and distribution of gasoline with (effectively) just keeping hydrogen in a bag. As already observed, it would certainly not be safe to keep the hydrogen in this way long term, because hydrogen seeps out and air seeps in - so eventually there would be enough air in the hydrogen enclosure (~25% at 20 ^OC) to form an explosive mix. There are also potential risks with hydrogen getting entrapped unless the whole system is enclosed.

If you get things right, small short-term buoyancy requirements (e.g. weather balloons) will always be most economically met using hydrogen. However, hydrogen becomes more dangerous as the system size grows and/or usage periods increase. (Hydrogen is of course particularly dangerous if there is a secondary enclosure to which it could flow)

Personally, I don't know whether we are looking at "horses for courses" or "unnecessary overcaution" following fires in inappropriately designed systems (R101 and Hindenburg)

Your talking about latex weather balloons? I would not use them for named flight. Even if it were in a ripstop shroud . Just one little pin hole develops from rubbing or what ever , And POP ! time to chuck the laundry . Urethane coated rip stop nylon is what the Parabounce and King fisher Aerostats use. It will take the abuse of outdoor life. and the containment is only 22- 23 ft in dia. for this personal airship. If you were of less weight , a smaller one could be used.

It is a single surface envelope so when the H seeps out molecule at a time it disperses into the atmosphere.

The envelope prior to filling would need to be sucked down with a wet vac to remove all the air . The hydrogen fill hose purged to remove all air , then you can safely fill the envelope. You may have a .001% of air still trapped in the envelope But that is acceptable .
Re filling or topping off while in use would require a grounding system prior to fill to make sure there is no charge buildup in the aircraft. Just like is required with any aircraft prior to refiling . Again the fill hose should be purged and the fill port should be a quick connect air hose type fitting

Clearly I wasn't suggesting weather balloons for manned flight. In any case, only the smallest ones are liable to collapse in the way you describe - if only because having a high internal pressure is wasteful of valuable lifting gas.
The intent was merely to point to an area where the potential hazards of using hydrogen are not considered problematic. The existence of such an area of use strongly suggests that manufacturers and regulatory authorities will have investigated the possibility of using hydrogen as a lifting gas for other applications - so if they do not suggest its use you would be wise to investigate the background before adopting it.

The current situation is that:
Parabounce state that their product uses for "intrinsically safe" helium. This is no surprise, as their product is intended for use in enclosed spaces.
Aerial Products (including Kingfisher) on the other hand are intended for outdoor use. However, there websites too specify helium, with no suggestion that hydrogen could be safe.

A purely pedantic point - which could be due to inaccurate product descriptions: my understanding was that Kingfisher used uniform polyurethane sheet that was inside a nylon outer web; I suspected they were welded together, similar to other light-weight enclosures I have seen, though this is not described on Kingfisher's website.

Wheew ! Good , I hear 'weather balloon' and automatically think latex and lawn chairs.
I do stand corrected. 2 variants of the King fisher. One is a urethane Bladder with a second ripstop shell. The other is coated nylon.
Yes , good point . I would call them and ask some questions about filling their ship with hydrogen . Maybe it all boils down to proper gronding issues when landing . But on the onset, it seems like there would be no problems.

"call them and ask some questions about filling their ship with hydrogen"

Given they have no control over how you use the product, and how litigious society has become, I doubt they could give a positive answer regarding hydrogen - even if they have no reason to consider it unsafe when used sensibly.

But if I really wanted to try it myself I would first undertake some experiments to see at what point things might become dangerous. You just need a friendly farmer

Yes, typo, should be CH4? burns very well.

Graphene! Graphite (pencil lead) membranes 1 atom thick.

There is a huge amount of research into graphene at the moment with some companies predicting production volumes of LCD screens in the next 5 years.

Plus this:- http://www.livescience.com/technology/080811-thinnest-balloon.html

Quote

"By experimenting further with bubbles made of graphene, McEuen and his colleagues found the membranes were impermeable to even the smallest gas molecules, including helium.

"It's amazing that something only an atom thick can be an impenetrable barrier. You can have gas on one side and vacuum or liquid on the other, and with a wall only one atom thick, nothing would go through it," McEuen told LiveScience."

Even if you can't get continuous graphene sheets, overlapping sheets within a suitable matrix sounds useful.

It's not directly relevant, but I'd still be dubious about "completely impenetrable". Specifically... hydrogen ions.

Excellent!

so all we need to do is find a flexible material that can act as a substrate for the ballon and put the graphite on the inside... What other materials will graphite bond with?

Even if it slows down the helium leakage by 50%, a new era of ballooning could take flight.

Chris

If you could get continuous film, the graphene would be remarkably strong - and flexible. Theoretically a hot-air-style balloon fabricated from a single graphene layer with a diameter of just 1-metre near the base could support a 30-kg load.

If we look at using horizontal tubes, we find that a graphene envelope with tethers spaced 1-metre could support 10kg/sq-m.

Of course, such large areas of continuous graphene are unlikely to appear in any of our lifetimes. The best we can hope for is probably mm-diameter sheets that would be held together in a matrix. The difficulty will be to orient them with the film and to ensure that the gaps between layers of graphene are small enough that leakage along the gaps between films is small enough (whatever that is)