Hi ,
I am trying to do some calculations to design a system to flush out a chamber of an evaporating contaminant. I was looking at
http://www.belljar.net/71leaks.pdf and set up a spread sheet using the Hagen-Poiseuille equation on page 6. Somehow I am getting something wrong as the result I get for nitrogen at 760 tor is coming out to .46 cubic meters a minute not 4.6 cc/min for the example Steve uses of a 36 in length of .007" dia capillary tube. I know it must be something stupid that I am missing.
Diameter=0.007"=1.78E-04 meters
Length=36"=0.9144 meters
P1=760 tor=101324.72 pascal
P2=0.01tor=1.33322 pascal
Viscosity of nitrogen 1.80E-05 pascal/seconds
here is the formula from excel
=((PI()*(0.000178^4))/(128*0.000018*0.9144))*((101324.72+1.33322)/2)*(101324.72-1.33322)
Which yields 0.007684436 Pascal-m/s if i understand the formula units correctly which when multiplied by 60 =0.461066182 Pascal-m/min this is several orders of magnitude greater than the 4.5 scc/min Steve refers to in the article.
What am I missing?
