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Vacuum System - Air Leakage Calculation Question

vacuum air leakage inerts

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#1 Top_Gun

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Posted 07 March 2018 - 11:07 AM

Fellow Forum Members,

 

I am working on a vacuum system and looked for a resource to estimate the air infiltration into the various vessels that are connected to the vacuum system, and I came across the following resource:

 

https://books.google...leakage&f=false

 

The attached table shows how the result of the correlation varies for the same size vessel at the various defined ranges of pressures.

 

Please see attachment.

 

Now my thoughts/questions...

It strikes me as odd that the air infiltration into a vacuum system would decrease as the pressure in the vessel decreases.  In my way of thinking, as the vessel pressure decreases, the driving force for the atmosphere to get into the vessel increases, which should result in more infiltration.  I am not doubting the correlation, as the references are certainly credible.  Instead, I'm attempting to get my mental mapping of this correct.  I suspect that I may have the chicken and the egg improperly assigned in my thinking.

 

To further aid in helping you to see what I'm requesting, I have listed two options that I thought of for how this result (lower air intrusion at lower pressures) may be possible.  That's what I'm seeking: the explanation behind why the numbers calculate as they do.

 

Option #1: Maybe it's that the vessel/system designed for lower pressure will inherently have less leakage.  (I doubt this is the solution to my mental quandary, for a variety of reasons.)

 

Option #2: The fact that the vessel is at higher pressure is indicative that it necessarily does have more air leakage because the infiltration of inerts causes more strain on the vacuum system which, in turn, causes the operating pressure to be higher.  (This, however, seems like circular logic.)

 

Any insights would be greatly appreciated.

 

Thank you.

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Edited by Top_Gun, 07 March 2018 - 11:22 AM.


#2 Saml

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Posted 07 March 2018 - 03:19 PM

Your option #1 is the correct one.

 

From the book "Steam Jet Ejectors form the Process Industries" by Robert B Power (If you happen to get hold of a copy, grab it! It saved my day while dealing with things like "broken" ejectors, backfiring el al.):

 

The heat Exchange Institute....recognizes that removing air from a low-pressure system is more expensive.....thus a low-pressure system will have a more stringent standard that would apply to systems operating at higher pressure......The HEI standard contains a chart which quantifies the air leakage associated with....systems regarded as "commercially tight"
 


#3 breizh

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Posted 07 March 2018 - 07:33 PM

Hi ,

Please consider the resource attached , from GEA .

Hope this is helping you.

 

Breizh

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#4 Top_Gun

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Posted 09 March 2018 - 07:19 AM

Saml,

Thank you for the quote from the Ejector book.  That's definitely insightful relative to the source that I found which gives a regression for the HEI leakage curves.  The book sounds like a good one, so I searched online to try to find a copy, and the cheapest one I could find is $418, so it must be a great book!  I guess I'll have to hope for a reprint, but I do appreciate the recommendation.  Good books for the profession are prized resources.  I use Kister's Distillation series all the time.

 

Breizh,

Thank you for your reference.  The data table on page 20 helped to further understand Saml's response above.  If possible, I may try to use the method suggested on page 19 to calculate our leakage on the next startup of the process unit.

 

______________________________

 

I guess it was a chicken and egg scenario after all, and the solution ended up being the option that I most doubted when I was trying to think through it!

 

Thanks again to both of you.


Edited by Top_Gun, 09 March 2018 - 07:27 AM.





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