Quote: (Originally Posted by
dive2dive2000)
Stuart, are you saying the deeper you are the more CO2 you produce? I do not understand "reaction front" or "depth of reaction front" I have never heard that terminology before?
No but the deeper you are the more scrubber material is needed to absorb the CO2.
Think of it this way - Lets just imagine there are 1000 molecules of gas in the loop at the surface and when you breath you produce 10 molecules of CO2. To remove the 10 molecules of CO2 you use, lets say 1cm 'depth' of scrubber material when at the surface.
eg 1 cm of scrubber material is enough to filter our 10 molecules of CO2 per 1000 molecules of gas. You need that much because not every molecule that bumps into your scrubber material is CO2 and if you only had .5mm then some molecules of CO2 would sneak through along with some of the normal gas molecules.
Now lets Image we were are 40m or 5ata - so this time there will be 5 times more molecules of gas in the loop - eg 5000.
Now for your scrubber material to be able to ensure that those 10 CO2 molecules are absorbed then 5cm of material is needed. If you only had 1cm of material then a bunch of CO2 would sneak through with so many molecules of normal gas. So the depth of the reacion front needs to be so much more.
That is why the deeper you are the shorter the run time of your scrubber - so lets just say a scrubber was 10cm tall - after lets just say 30 mins on the bottom you had used the first 5cm. Then at any moment you would start getting breakthrough at 40m as the reaction front or the total amount of scrubber material being used was 5cm - eg the total that was remaining after using the first 5cm.
But when you come shallower then the reaction front gets smaller eg lets say at 20m it would only be 3cm, now you have 2 cm left of scrubber material that isn't being used.
Hope that helps.
Stuart