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Sent PM to Molecolar products, and here is the similar text for interest:

The article states that low flow is favorable to the reaction by maintaining a compact reaction front.

The question relates to geometry rather than "flow" since it is the combination of flow rate and geometry that determines gas velocity through the scrubber.

In two identical rebreathers, say one has an axial scrubber, the other has a radial scrubber. For simplicity, let us assume they have the same amount of scrubber material and a similar geometry, i.e. a long-ish cylindrical scrubber. This means that both machines have the same mass flow rate assuming identical divers.

Which is likely to have the highest scrubbing efficiency?

The radial machine is likely to have the lower gas velocity profile within the scrubber material, but has more surface area and therefore an inherently less compact reaction zone because of the gas distribution. The radial machine has a lower beathing resistance given the cross-sectional area advantage over the axial machine.

The axial machine has the lower cross-sectional area to the flow, and therefore higher gas velocity through the scrubber material. Given the lower cross sectional area, this design is susceptible to have a more compact reaction area, however higher gas velocities would tend to impede the absorption process.

This assumes that concentration gradient driven diffusion processes are the dominant means by which the CO2 is absorbed.

The question therefore is whether scrubbing efficiency is the same in both these scenarions, or whether a lower gas velocity is the distinct advantage for scrubbing efficiency.

best,

z