Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Typical vacuum/pressure in a domestic vacuum/Thermos flask

Typical vacuum/pressure in a domestic vacuum/Thermos flask

Typical vacuum/pressure in a domestic vacuum/Thermos flask

I am trying to replicate a vacuum flask (on a low budget) with a 1m long 8 inch UPVC pipe forming the outer shell. A search of the internet suggests that the influence of convection stops around 10 Pa, however the vacuum pump I have, a two stage rotary 3 cfm advertised to achieve a vacuum of 2 PA, can only achieve around 350 Pa. My question is, what is the typical vacuum/pressure in a domestic vacuum/Thermos flask and how is it achieved? i.e. a vacuum pump or creating a void in the manufacturing process.

RE: Typical vacuum/pressure in a domestic vacuum/Thermos flask

When we made them in the lab we always used 10E-5 Torr (1mPa) as an upper limit.
For large bulk storage tanks the limit is not as low, I recall using 0.05mbar (5Pa, ~40mTorr).
There also contain multilayer aluminized mylar foil in the vacuum space to reduce heat transfer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Typical vacuum/pressure in a domestic vacuum/Thermos flask

Thanks LittleInch and EdStainless, I'll just have to find a better pump. One thing EdStainless what volume do you consider to be bulk storage and why do you think this to be the case.

RE: Typical vacuum/pressure in a domestic vacuum/Thermos flask

Thousands of liters is bulk storage, you know tanks that are 20' tall and larger.
It is twofold, there are limits on what is practical with that size installed outdoors, and they make up much of the difference with the layered aluminized mylar film.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close