Can a vacuum balloon float like a helium balloon?

[jetwaterluffy]

Sure. That would work, provided you keep it hot enough.

You're talking about a hot air balloon, aren't you?

 

[akhmeteli]

What criterion are you using for buckling?

In this case I use the classical Zoelly formula for thin spherical shell buckling (see my patent application or http://books.google.com/books?id=6P...age&q=zoelly spherical shell buckling&f=false , equation 5.2 .

And why do you think that equation is applicable to Kevlar, which is an anisotropic composite?

Because even if you substitute the kevlar compression modulus for the stiffest direction (say, 76 GPa; you can even substitute the value of the kevlar fiber tensile modulus - about 180 GPa) in the Zoelly formula, the critical pressure will be much less than the atmospheric pressure for radius of curvature R=6 m and the shell thickness h=0.9 mm.

 

[NascentOxygen]

The density of air at sea level at STP is 1.25 g/L.
The density of pure nitrogen gas (N2) at STP is 1.29 g/L

I think you need to double-check those densities -- they are obviously not at the same T and P.

Yes, chrisbaird has his figures wrong way round.

air at STP 1.293g/L
N₂ at STP 1.2506g/L
He at STP 0.1785g/L

 

[DaveC426913]

Yes, chrisbaird has his figures wrong way round.

air at STP 1.293g/L
N₂ at STP 1.2506g/L
He at STP 0.1785g/L

So, a one litre balloon of N would have to have materials weighing less than ... 42g.

 

[chrisbaird]

Yes, chrisbaird has his figures wrong way round.

air at STP 1.293g/L
N₂ at STP 1.2506g/L
He at STP 0.1785g/L

Oops. That's why I'm a theorist. I just lifted these numbers (not so carefully) from wikipedia. The point is that it's all about densities and as air is mostly nitrogen, it it not much different from pure nitrogen as compared to Helium.