Axial Scrubber Design Comparison

teksimple

Yep, me too. "Supposedly" more sorb is exposed (more dwell time?) to the gas in each breathing cycle with a radial or annular axial, compared to axial scrubber. I haven't thought of how to figure this quantitatively, perhaps a calculus function using the scrubber face as a plane, integrated with the the distance to the center of each sorb grain?

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richc

It depends on how you want to model it (continuum or particulate). Given grain size, Van der Walls forces will be pretty much negligible so I'd model it as a continuum. Quantitively you need to resolve the Navier Stokes equations using cylindrical co-ordinates. Mathematically speaking the difference between axial and radial is that with an axial scrubber you're only getting net gas movement on the z axis, whereas on radial you can have net gas movement in both r and z planes and the pressure gradient isn't linear with respect to r and so velocity has a gradient across r resulting in dwell time changes. You can also add the curvey fins (like in my Boris!) to get movement in the theta plane too.

Hope that makes some kind of sense

Cheers
Rich

mempilot

Interesting topic. I have a question about the difference between a standard Meg scrubber and a Mini Meg scrubber then. It seems to me that since the diameter is the same, and the inlet and outlet diameter are the same, but the length of flow is different, then the 'flow cone' would be a different shape. Would this mean that the difference in scrubber times between the two scrubbers would not be linear in fashion, since the volume of the cone size based on it's shape would not be linear as well? Does that make any sense? I may not have stated that properly.

In other words, if the Mini Meg scrubber is hypothetically 2/3 the volume of the standard Meg scrubber, the duration may not necessarily be 2/3 that of the bigger scrubber due to the way the gas flows through from bottom to top and forms a more squat cone.

?????

I'm just a crude instrument, so a little help with the physics if you will...

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mempilot

Another question: My Movie Meg came with the ExtendAir adapter. This adapter allows the gas to flow through a perfect cylinder scrubber with no restriction on the exhaust side. After the gas exits the scrubber material, it enters a chamber that then funnels the gas to the Meg head inlet. This seems more efficient in that a cone probably wouldn't form in the scrubber itself. If this were true, then why not design a granular scrubber that allows the gas to flow through equal diameter inlets and outlets before it is directed to a smaller head inlet?

Also, in a normal axial scrubber, since the top outer edges of the scrubber material don't seem to get used, why not design the scrubber to be more of cone shape, eliminating wasted material. The scrubber shape would facilitate what is naturally occuring anyway. Maybe the cost to build such a scrubber would not be justified in the little savings it would create in reduced volume of sorb needed to fill it?

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MEM "Da Pilot"

Black holes are where God divided by zero.

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"Donkey's kill more people annually than plane crashes."

jeff h

That's probably not a bad idea, however there is also dwell time in the scrubber. Although the majority of the flow doesn't go through the top edges I have to believe it will still scrub some gas, especially once break through has started. Having extra sorb in a "reserve" location could be a good thing.

I'm sure the real answers are much simpler - don't push the scrubber and get a radial scrubber if you want an optimized design.

mempilot

Agreed 100%. I just did three hours yesterday on my standard axial scrubber and the coloration was up from the bottom about 1/3 with the clumped or hard sorb within a couple inches of the top. The outer portion of the top was packed, probably from being moist. I did 4 hours in shallow water during training, but I wouldn't do that on a real dive. It seems 3 hours is what I would call safe in my book, fully knowing that Leon pushed it much further in testing. Something to note: I'm conservative, and I also am mostly diving in warm water. If I start doing more long cold water dives, I'll invest in the Golem radial scrubber.

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MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

Rebreathing Red

The warmer material can adsorb more CO2. It will last longer.

flow.bmp

deep_flow.bmp

jeff h

Yes, but all of the material has same potential to start with. As the material warms up it also speeds up the reaction so it may not necessarily mean "it lasts longer". The slower reacting material may actually "last longer" since it will also be able to absorb more CO2 as it heats up.

What is really scary about the point you made is as break through starts to occur the loop will cool down which will affect the efficiency of the remaining granules and expedite total break through.

Independent of the shape of the cone it looks like there could be a difference from center to edge though. So if that is the case I still wonder which design is more efficient or stable.

Thanks again,

-Jeff

ibbo

just to clear it in my head, does used scrubber material flow better or worse than fresh? or the same for that matter. the meg has a clear scrubber housing, and you can see a colour change in std sofnolime when it has dried out. the used being whiter.

i ask this because at times i can see areas that are still the original colour. doesn't always follow a pattern, and only shows on cold water diving.

i am assuming! that after a few minutes use the water content will be fairly even throughout the scrubber and it can be ignored as far as causing a variation in flow?

ibbo

from the new hse video it seems that used lime flows easier than unused, so surely the radial scrubbers with a shallow depth of scrubber have a serious potential short coming. if there is any direction in the flow at the input side then it would lead to a very early breakthrough.

so, is there a radial option for a side fed scrubber, a la inspo?