RE: An Exercise in Pipes....1 Jul 2021 23:44
Hijacking your thread.
Having pondered everything said and DM's mention of Boyle's Law (except he mentioned temperature), I would like to provide a note of caution concerning % announcements.
The pressure goes up the further down you travel and visa versa. E. G. Airplanes and mines. In the mine the column of Air above you is greater the deeper you go. So at the bottom of a drill hole the column of Air is greater and the pressure is greater than at the surface. However, that can only be so at constant temperature. I don't know what temperature changes occurs at depth compared to the surface, but I suggest it is considerable. Therefore, working out the number of Helium molecules in an environment at rising pressure is not easy. Temperature will inversely effect this number of molecules too. Lower temperature will result in gas molecules being closer together, taking up less room, or conversely contain more of them per fixed volume. Pressure increase has the same effect. That is a difficult position to assess when attempting to ascertain He concentrations.
Imagine also you are climbing Everest. As you go up the air gets thinner (opposite to the mine or drill hole). However the % mix of Oxygen to Nitrogen remains the same. Hence you can breathe, but have to do more work as there are less Oxygen molecules in each intake of breath.
Conversely, down the hole it is more molecules, but the % stay the same.
So when you are considering a percentage of Helium in Nitrogen at the bottom of the hole, it will probably be the same as at the top, unless you encounter new sources of He from below seeping into the hole. Measuring the % of Helium does not tell you much without knowing its pressure and temperature to see how many molecules of it are gathering.