# Thermodynamics: PPM, Volume, and time into leakage rate. Gas Laws, Helium

1. Aug 31, 2011

### mbarl/s

This is a question which is very relevant to my work. I wasn't sure where to post. I am an engineer and not an expert in the field of Thermodynamics. I have a sensor which works at atmospheric pressure and shows the concentration of helium in parts per million in the air.
I have been given an undocumented/uncommented program which takes the change in PPM, the residual volume of a chamber and the time over which the PPM is changing. From this, it works out the Leak rate of an item in the chamber in Pam^3/s.

The relevant code works out in maths as the following

q=(V * rho<air>* (R*104) * 5863 * C ) / (2*1015)*M<air>*100*t)

where:
q= leakrate
V=volume in ml
rho<air>= density of air
R is the universal gas constant
C=concentration in PPM
M<air>= the molar mass of air
t=time in seconds that the linear increase in PPM is taken

None of the constants were initially commented so I have remembered that some constants are rho<air>, R and M<air> from my elementary knowledge in thermodynamics.

My problem is I have no Idea what the constants 5863; 2 quadrillion(2*1015) and 100 are for. I also don’t know why the UGC is multiplied by a factor of 104 but at least I know what it is.

Basically I need to know how the program works to see if it needs any improvement. If anyone has any ideas was to what the constants are or what they relate to that would be a great help.