Poiseuille's Low manual calculation

Question

Hi everyone, Trying to manually calculate a column flow using the Poiseuille's Low equation. I know there is the Pressure Flow calculator, but I need to understand how it's calculated. I have all initial data (column dimensions, pressure, temperature, carrier gas viscosity) I need. Does someone know the right way to do it? I have been trying several ways, used different units, triple checked my math, but always had a value which is not even close to the flow value calculated by the Pressure Flow calculator. 
 I have a feeling I do something wrong. Please advice some calculation flow. Thank you.

CMZainea · Answer

Hello igorvlad 
 
 I&rsquo;m sorry for the delayed reply to your message. Do you still need assistance with this? If you do, please take into consideration the notes below. However, if the issue was resolved, could you please share what the resolution was? 
 
 From what I remember, the Poiseuille's Law equation has a general form, and a somewhat different (modified) form for GC flow calculation purposes. In other words, it needs to take into account compressible gases (from my understanding). While I don't know how the Pressure Flow calculator calculates that, I can't imagine it uses something different than Poiseuille's Law (in one of its available forms). 
 
 There is another Agilent Community post, on a different subject, but that contains one of the possible formulas you may be using. Please feel free to check the formula posted in there and see if it matches what you were using. 
 GCMS-FID Split question - Forum - Gas Chromatography - Agilent Community 
 If it doesn't, what formula(s) were you using, what are the parameters and what are the values flow values you are getting, as well as the ones from the calculator?