×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# Vavuum Chamber Design - Air Permeation Calcs

## Vavuum Chamber Design - Air Permeation Calcs

(OP)
Hi,

I am trying to solve an air permeation problem through a polymer seal but i don't have any experience in vacuum technology. I worked on this problem a bit but not sure if my approach is correct.....

Let's say I have a cubical Glass vacuum chamber (volume V) with initial high vacuum about 10-5 torr. (No more pumping to maintain this constant).  The chamber has a rectangular seal of area 'A' on one of its sides which is exposed to atmosphere. I would like to calculate the reduction in vacuum pressure with time because of air permeation through seal alone.

I know the permeability coefficients of each of the species in air. The question I have is about the pressure difference in the following equation.

According to the hand book of polymers, Permeate leak amount (of any species in CC),

Qi=  Pi x t x A x (P_Out - P_In)/L
where,
Pi - Permeability  Coefficient of N2,O2,Ar, etc ( in cm3-cm/cm2-sec-Pa)
t –  time increment  in seconds
A – Seal Area (exposed to air)
P_Out – atmospheric  pressure? ( or is it partial pressure of each species in air)
P_in  –  instantaneous  vacuum pressure ( again is this the total vacuum or partial pressure of each gas inside the chamber?)
L - Seal thickness

Currently I am using the atmospheric pressure (101325Pa) for P_Out and using the instantaneous vacuum pressure for P_in,  but multiplying the diffrerence (P_Out-P_In) with the volume fraction of each species as follows.

For a small time increment of dt,  Q_N2 = P_N2 x dt x A x (P_Out - P_In) x 0.78/L

Q_Air (in CC)= Q_N2 + Q_O2 + Q_Ar + Q_CO2 +....

Also, once I get Q_Air, I am calculating the reduction in vacuum assuming Air obeys Ideal Gas Law under vacuum:

P_reduction  =  nRT/V where n=Q_Air/22400 , R-Gas cont, T-ambient Temp in K, V-chamber vol

Am I doing it correct or it's not this simple? Any help is greatly appreciated.

Thanks,
Nodal

#### 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.

#### Resources

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
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!