Correlating Leak Rates for Helium, Air & R134a - Michael

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Discussion Overview

The discussion revolves around correlating leak rates for different gases (Helium, Air, and R134a) under varying pressures for a specific application. Participants explore methods to unify leak test specifications and seek assistance with variables affecting the calculations, particularly focusing on compressibility factors and gas properties.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • Michael seeks to correlate leak rates of Helium, Air, and R134a to standardize testing methods, expressing uncertainty about the compressibility factor and real gas density for R134a.
  • One participant suggests that for small leaks, the leak rate is influenced by pressure difference and gas viscosity, indicating that viscosity varies with gas type and temperature.
  • Another participant mentions the concept of choked flow in leakage rates and recommends a specific website for calculations, despite expressing reluctance due to the site's reputation for spamming.
  • Michael acknowledges the need for additional information and requests further suggestions to assist with his problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to solve the problem, and multiple viewpoints regarding the factors influencing leak rates are presented.

Contextual Notes

Participants highlight limitations in available data, particularly regarding properties of R134a and Helium at different pressures and temperatures. There is also an acknowledgment of the complexity introduced by gas viscosity and flow conditions.

djsnow
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Hi
I am i new member, i hope i am posting in the correct forum. I require some help i with a problem i am trying to solve in my work. Currently we have 3 separate leak test methods specified for a part all with different working gases and pressures. If possible, i would like to correlate this data so that i can determine that a specified leak rate of "X" with Helium at 700kPa is equal to a leak of "y" with Air at 1.0MPa is equal to a leak of "Z" with R134a at 2.1MPa. The aim being to commonise to one spec (preferably air).
I have done some work on this to based on info in found around the web, in particular this site:
www.air-dispersion.com/msource.html
I am struggling with a few variables used in the formula, in particular compressability factor and real gas density and a few others of R134a.
My question, is there another way to go about solving this problem that anyone might be able to help me with? Does anyone know where i can get some properties tables on the web on R134a at different pressures and temps (and helium for that matter) that could also assist me.
Thanks in advance, any help you can offer will be greatly appreciated.

Michael
Australia
 
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I think that your are concerned about small leaks. If this is the case, the leak rate is determined by the pressure difference and the gas viscosity. And this is the main word: viscosity. It depends on the gas and on the temperature. You can learn about this in wikipedia.
The reference that you give if for "big" holes.
 
Thankyou, i will look into this but i still think that i will need some information that i do not have, any oher suggestiong would be helpful.
 

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