The imbalance of CO2 absorption of the rebreather scrubber

[justinthedeeps]

The diagram is from Molecular Ltd. Can you specify which studies and simulations show the flowfront as a cone?

Hi yeah sorry I should include a reference for that. One example is these thermokinetics simulations, I think there is a study article associated with this:

The hot/reactive part of an axial scrubber tends to be in its core, rather than the periphery. So breakthrough is thought to usually occur right up through the center of the canister, as the material gets chemically exhausted.

I think this has also been measured in real experiments, but will need to look for the actual references.

But it is also possible to get channeling elsewhere, in a poorly packed or poorly designed canister. The gas will follow any path of least resistance.

Resistance to flow is probably much more important than orientation. Warm gas is free to rise if it is in a void, but it is not free to do so in a closely packed scrubber.

I/we also see this in axial scrubbers that get hit pretty hard (increased exertion and/or duration, increased loop moisture, etc). When you dump out the absorbent, there will be a cone of partly clumped/fused material in the shape of a cone in the center of the used scrubber.

This is probably caused by the heat and moisture dynamics occurring mostly in the center core, rather than at the outsides or 'top' of the scrubber.

 

[justinthedeeps]

I think also in response to your original question, yes you are correct overall that some parts of the scrubber might never be fully utilized, due to different flow dynamics and thermokinetic properties of the scrubber. They say that the localization of heat plays a big factor in the reactivity of the canister.

I think it is probably true that a calmly breathed (low flow rate) canister has a more uniform utilization of the absorbent material, and more even thermokinetics.

A canister being breathed from heavily (with higher CO2 and flow rates) is likely to have more uneven flow characteristics, and thus higher risk of premature breakthrough that bypasses unused absorbent.