Force Cause by Running 60psi of Gas Through a Glass Tube, While the Tube is In a Vacuum

[Zibraz]

I'm looking around for some answers and i'm struggling to get much online, and my college notes didn't go into this.

I'm researching for a design we might have to look into soon. I have a glass tube which is leak tight but kept at 60 psi with Helium glass running through it. This glass tube will be going through a vacuum chamber (The vacuum chamber is required because the glass tube will be cooled in this area to below -100°c, the vacuum chamber removes moisture from outside the tube).

where can I find resources on determining the force which the tube would be experiencing under this vacuum? The glass tube is strong enough to hold 60psi, but when it enters the vacuum chamber the pressure difference is going to cause more stress on the glass tube. Fusion and Inventor aren't able to run this analysis (I can run a normal stress FEA, but i'm unable to simulate the pressure difference)

Thanks.

 

[1503-44]

A vacuum could add another 15psi to the differential pressure between inside and outside of the tube. Design the glass tube as usual for a minimum of 60 psiG plus another 15psi = 75 psig (equivalent internal pressure at sea level).

 

[Compositepro]

If you are worried about stresses caused by a 15 psi vacuum, just wait for when you have to deal with the thermal stress issues between the glass tube and the vacuum chamber.

 

[LittleInch]

Mr 44 is correct. your tube needs to be able to withstand 75 psi of internal pressure.

But the key issue could be how the tube is sealed into and out of the vacuum chamber.

How's it being cooled in a vacuum?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

I just kinda thought it would be flowing cold helium gas. Don't really know, but kind of logical?

 

[LittleInch]

"The vacuum chamber is required because the glass tube will be cooled in this area to below -100°c"



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Yes, if that's cold helium gas flowing inside would freeze moisture on the outside surface.

 

[LittleInch]

Ah. Now I get you.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

A small ice cube factory.

 

[3DDave]

Wouldn't a dry gas surrounding be as good as a vacuum for keeping it dry? Argon is a good choice.

 

[Compositepro]

Vacuum is a better insulator than any gas.

 

[1503-44]

A vacuum has no moisture content, so even insulation is redundant.

 

[Compositepro]

If you re-read the OP you will see that the purpose of the vacuum is likely for insulation.

 

[1503-44]

Probably both

 

[3DDave]

I don't understand the need for a glass tube for helium to flow through.

The stated requirement is "the vacuum chamber removes moisture from outside the tube" not "and keep the heat transfer limited" which would also include the expected effect or restricting heat transfer. Heat will still transfer to the tube at the attachment to the wall of the chamber, right? That connection will be substantial to maintain the vacuum and maintain the 60 psi so the ability to transfer heat will be high.

 

[1503-44]

Its obviously a quantum computer.

 

[Zibraz]

I didn't realise I had so many replies here. I didn't get notified.

So currently, this question is in relation to upgrading our current assembly. We have a glass tube going into a relatively sealed "Box" (This box can maintain a higher pressure than 1 atmosphere). Heat is removed from the glass tube with peltier coolers. We pump dry air into the box which removes moisture, we can reach pretty decent temperatures with this arrangement.

We are trying to cool this tube down further. We are finding that the air is causing alot of the walls of the box to become very cold. By removing the air from the sealed box, we should be able to achieve colder temperatures while also removing moisture. I know we will get some heat transfer from the required o-rings, and where the tube touches the walls of the container, but removing the air as much as possible should improve our cooling capability. We managed to reach -70°c so far, creating a vacuum seal was on avenue we were going to investigate.