That’s a nice reference. Note that it talks about effusion (is the term I think) through a porous membrane (rubber). I don’t think it can be generalizable to modern envelope materials you would consider for a hydrogen or helium aerostat, as they should be impermeable to oxygen.
Clicking though links on Wikipedia got me to here:
Reference [2]:
Thanks for the two links. Both are related to endosmosis as defined by the links I provided, but in different areas ranging from biology (membrane) to Graham’s effusion law (also called Graham’s diffusion law), and relating phenomenons such as effusion, diffusion, permeation, endosmosis, exosmosis …
From Graham’s effusion law: “Therefore, hydrogen molecules effuse four times faster than those of oxygen.”
If there is no other factors preventing the following (such as the size of atoms or molecules), that implies that air enters in a helium or hydrogen aerostat (in a lesser proportion than the helium or hydrogen leaking) and confirms the old experiments and the recent observations from Dave Santos and some other.
All the papers and indications about gas balloons and airships mention leaks. And leaks occurring should imply that some air enters in the aerostat, apart perhaps some possible factor I mentioned above. Modern envelope materials mitigate leaks, so they mitigate also the entering of air, but without cancelling them as perfectly as a hydrogen-tight metal tank would do. However perhaps some modern envelope material would not be air-tight to hydrogen (leaking) while being air-tight to air (not entering), or air-tight to both: it is a point to check.
https://www.researchgate.net/publication/259504329_Graphene_An_impermeable_or_selectively_permeable_membrane_for_atomic_species
As the air-hydrogen mixture is explosive, the effusion concern is very important if we want to try to make hydrogen safer for aerostats that are used for a long time.
That person would seem to be the one to ask.
My first questions for this topic would be, where could you buy a helium balloon, how expensive is it, how expensive would it be to fill it with carbon-neutral hydrogen, and how much hydrogen or helium would it lose over time?
But to continue this exploration of diffusion through a membrane, maybe this is relevant:
07979_intro1-5.pdf (301.5 KB) [Plastics Design Library] Liesl K. Massey - Permeability properties of plastics and elastomers (2003, William Andrew).rar (2.4 MB)
07979_thermopl1-15.pdf (453.2 KB) 07979_thermopl16-32.pdf (391.1 KB) 07979_thermopl33-46.pdf (460.4 KB) 07979_thermopl47-60.pdf (393.2 KB)
If Windy Skies would experiment with balloon envelope materials, the following effects would be easily observed-
-Overly heavy material may hold gas well enough, but the excess mass is highly parasitic to lift performance.
-Thin-film high performance gas-retention materials suffer from rapid degradation in practical use.
There is a mysterious aspect to rapid loss of gas-tight performance. My old theory in the LTA field proposed that static electricity (corona discharge) punches microscopic holes. Quantum tunneling of molecules is a related analytic prediction.
This is perhaps the most thorough discussion on permeation I have been able to find:
This is probably the most helpful resource on permeation I have been able to find:
The source provided further substantiates the well-established LTA gas leakage problem.
Fortunately, AWE need not depend on LTA gas, with all the hidden engineering shortcomings in cost, complexity, and performance.
