continuous Trimix blending using 2 nitrox analyzers

[sprockjohnson]

For blending the HE first and for making 10/70 the equation regarding the first o2 cell would be pO2 air x (1- %inert gas besides air (for example HE)) or 0.21 x (1-0.70) and that would give you a pO2 reading on the first cell of 6.3% o2. You would then inject o2 after that but before the second cell to bring the reading back up to 10% o2 and analyze the final mix.

 

[rjack321]

The Ideal Gas Law is one, but not accurate enough at typical pressures. To do it more accurately is far more complicated than one equation, unfortunately. I suggest you check out the Gas Blender Toolkit.

The two-analyzer method is measuring at ambient pressure at the compressor inlet. You don't have to (and should not) adjust the percentages to account for compressibility. If you make 18/45 (or any other trimix) at the compressor inlet you will have 18/45 when you analyze the cylinder (your analyzer is also at ambient pressure).

 

[inquis]

Thanks for the correction. I didn't initially realize this was being mixed on the fly (before going in the cylinder).

I'm curious as to how much gas is typically wasted from such a blending approach. Presumably some valve is adjusted until the analyzer gives the correct percentage for each stage?