Creating a Long Life Helium balloon

[Laurencet]

Why do metalised film helium balloons only last about a week?
Could I improve this result and make a balloon float for a year? (and don't cheat and say just make it bigger) how do I stop it leaking?
Are there any better materials to make it from? (unlimited budget)

As I understand aluminium should have a permeability of virtually zero, Is the problem that they normally made from a metalized plastic and there are gaps in the aluminium? Does this leave voids in the material itself?
If I made if from a multilayer thicker foil would this be better?

What about the heat-sealed joints will the gas seep through 5mm of molten mylar or LDPE? (surely the area and leak path is tiny)

I guess the last thing is the knot, Could I heat seal it?

 

[hutchphd]

Have you ever had a latex balloon with helium?? Lifetime of hours.
I think the aluminum coating on the Mylar is almost irrelevant but stand to be corrected. It is very thin, and the Mylar is pretty good by itself.
You could keep your balloon in the deep freeze...

 

[Laurencet]

Latex balloons do well to last a day, helium is so tiny it just goes straight through. you can buy an additive to add to latex balloons called Hi-float that makes them last a few days but never a year. The helium can definitely go through the mylar ( I have a permeability coefficient of 4.2-20x10^-10 ) Why else would all food packaging etc have ALU if it isn't to reduce permeability. It certainly adds cost.

 

[hutchphd]

I'm not aware that all the packaging is aluminized. It does look good What are the units on the coefficient?

More than I really wish to know on the subject:
http://www.polymerjournals.com/pdfdownload/1088324.pdf

 

[Laurencet]

The units I quoted are

I'm guessing its products where you need to stop the water vapour and oxygen to keep it fresh for longer.

I still don't understand why foil helium balloons don't last longer.

 

[Laurencet]

I'm surprised no one can answer this question..

 

[TeethWhitener]

I don’t have this experience. I regularly buy metalized balloons from the dollar store for my kids’ birthdays that last for months. Sure, they deflate somewhat, but they’re usually still floating when I finally get rid of them.

 

[hutchphd]

As I understand aluminium should have a permeability of virtually zero

I don't understand why you think this should be true. Please justify your supposition and then it can be discussed on a rational basis.
Some quantitative references or calculations would help.

 

[Laurencet]

I don't understand why you think this should be true. Please justify your supposition and then it can be discussed on a rational basis.
Some quantitative references or calculations would help.

All metals have zero permeability, as the foil starts to get below 12nm we start to get faults and holes in the foil that allow for permeability.

 

[TeethWhitener]

All metals have zero permeability, as the foil starts to get below 12nm we start to get faults and holes in the foil that allow for permeability.

This is utterly false:
https://www.jstor.org/stable/96330?seq=1#page_scan_tab_contents

 

[Laurencet]

Very interesting...

I'm going to have to put some numbers into the equation, I'm now wondering if there is a critical thickness for aluminium for diffusion to take place.

• C. J. Smithells, C. E. RANSLEY
• Published in Nature
• DOI:10.1038/134814b0

THE rate of diffusion of gases through metals has been found to be approximately proportional to the square root of the gas pressure, and is generally represented by the equation. Borelius and Lindblom1 made accurate determinations of the rate of diffusion of hydrogen through various metals and found their results were more nearly represented by the empirical equation where Pt was a threshold value of pressure below which no diffusion took places.

 

[DaveE]

As I understand aluminium should have a permeability of virtually zero

No, molecules move (diffuse) through nearly everything unless there is some strong force to keep them in place, like a crystal, for example. In practice the rate of diffusion will depend on the thickness of the material.

However, I suspect the real issue is more likely related to the construction. Leaks at seams, pinholes, or cracks may be the dominant source of leakage.

 

[anorlunda]

Airships have a great interest in helium leakage. Below seems to be the best they can do.

http://www.blimpguys.com/helium.htm

A product with no holes will have about ½% to 1% loss per day through the material

Edit: By the way. I have found partially inflated Mylar party balloons floating on the ocean hundreds of miles out to sea. They float indefinitely until eaten by some sea creature. I think that is a big problem. Any party balloon lost into the sky may wind up killing a sea creature.

 

[Baluncore]

The biggest cause of He loss will be positive pressure across the envelope membrane. For that reason an elastic envelope should be avoided so only the differential hydrostatic pressure essential for lift is present. That requires the envelope be cut to shape and not filled completely.

If an outer envelope membrane was present to trap He lost by leakage, the leaked He would move up to the top between the double skins where it could accumulate before being pumped back into the internal envelope. There is an application for a solar powered pump there. There would still be a gradual diffusion and mixing of He with air, but not a one-way torrent. The double envelope would weigh more, but I believe it would significantly reduce the He gas loss.

Any party balloon lost into the sky may wind up killing a sea creature.

Yes, and the next creature that eats the victim, recursively.

 

[Laurencet]

Be great to put some numbers behind this..

Assuming the balloon is made from 2 discs 50cm diameter
We have an area of approximately 4000cm²

Pressure 0.1bar (75 Torr) above the atmosphere?

If we forget everything else in the foil lamination apart from the
Alu - Thicknesss 10μm

How do we calculate leakage rate?

 

[Baluncore]

How do we calculate leakage rate?

You measure it.
The differential pressure across the envelope does not forget or ignore everything except the metal film. The differential pressure is greatest at the top of the envelope, and zero at the bottom if vented. The leakage rate will be a some diffusion function of the differential pressure, integrated over the height of the balloon.

 

[Baluncore]

Pressure 0.1bar (75 Torr) above the atmosphere?

That would make it a very high pressure balloon.

A balloon, vented at the bottom, would need a height of several thousand feet to develop a differential envelope pressure of 0.1 bar at the top.