Vacuum chamber flat end-caps

[drodrig]

Hi there,

I have to design a vacuum chamber, big in diameter (~2.5m in diameter). On one end I have to use a flat cap, as thin as possible.

My first challenge is how to compute the stresses in this end-cap. I learnt how to calculate deposits with round endcaps (hoop stresses...). But how does one check this one it is flat?

thanks
regards,

 

[rb1957]

"foil" ?? you're going to make a vacuum chamber out of "foil" ... good grief !

you won't make a vacuum chamber, you'll make a little crushed bag of foil.

another day in paradise, or is paradise one day closer ?

 

[Nescius]

Large vacuum chamber eh? What could go wrong? It's only ~15 psi pushing in, right?

Check out the youtube videos of train tanker cars imploding because of drawing a vacuum on them. I assume they were being emptied with a pump and they weren't vented. It looks like a special effect out of a Hollywood blockbuster.

 

[rb1957]

Roark 7th Ed, table 11.2 case 10a

and Timoshenko dealt extensively with round plates (since they solve nicely !).

seriously, your options are ...

1) a flat bulkhead, but thick,

2) a flat thin bulkhead, but with stiffeners,

3) a domed bulkhead, can be thin (but I doubt foil will do it)

another day in paradise, or is paradise one day closer ?

 

[IRstuff]

"In principle bending is not a big problem, the problem is it should not break

It needs to be thin because particles go though it and we want to "see" them, if the material is thicker particles get "broken" in the material. ribs/bracing/stiffeners are also bad (more material)"

Absurdly mutually exclusive. Apparently you have not even run the calculation. Your 2.5-m diameter will have 56 tons of force on it. Anything thin will be ripped to shreds. There's a reason why flat vacuum chamber walls look like below. You need a few inches of steel to have it not buckle. Your basic premise as described makes no sense whatsoever. If it's permeable to ANYTHING, it'll be permeable to air, so even if you could pump down one side, the permeability will allow room air to rush into the other side and overwhelm the high vacuum pump. And why would you ever want a 2.5-m membrane? An inch or so would be more than enough to demonstrate permeation, and would allow you to have a mating chamber with only the species of interest. Even if the source is large, there's absolutely no reason why the interface has to be large.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[bnrg]

If the side opposite your thin wall is helium, can it be at a very low pressure to minimize the pressure drop across it? This reduces the structural load by what ever you can live with for the helium pressure.