Quote: (Originally Posted by
Scott)
Steve,
I am not an engineerer.. but..
I can see logic.. in both explainations..
By the flowing along the radius, the Radial scrubber is going either from a larger surface area, to a smaller.. or conversely from a smaller surface area, to a larger.
When passing through the larger surface area, it should have a lower velocity, and while passing through the smaller surface area, should have a higher velocity.. which is shown in theory in Paul's spreadsheet..
As you suggested that his explaination uses static flow, versus more human tidal flow.... I would think, would affect both designs similarly?
On the Axial design, it seems to me, that the dwell time would be Uniform for the entire scrubber, ... where as on the Radial the dwell time would be smallest at the inner diameter, and highest on the outer diameter.
I can see how this could be a negative, resulting in rapidly exhausting the scrubber in the outer diameter volume, and not allowing sufficent dwell time to utilize the inner diameter volume...
Maybe you could explain to me.. in regards to axial scrubbers, why it is more common to have tall, smaller diameter design versus a short, large diameter design.
In my mind, given the same volume, an nearly equivalent amount of gas passing through whether tidal or continual, (difference due possibly due to WOB).. It seems, that the larger diameter cannister would reduce the velocity of the gas such that the dwell time remains the same. In the smaller diameter cannister, the velocity would be higher.
My head hurts =(
Thank you for any education I will soon likely receive =)
-Scott
Hello Scott, first off if you look at a spent radial scrubber in-out flow, you will notice the spent sorb clustering around the inner tube and less color change on the outside edge, showing that most of the radial dwell takes place on the exhale side.
I think Steve is right that the tidal cycle is the missing factor in the comparison, it's the only explanation for why a radial works at all as without it and if the gas was flowing at a constant rate, it would fill up the scrubber and just keep flowing out at whatever rate the flow and restrictions dictate and would in fact be no different than an axial of the same weight.
Paul may believe that the pressure drop btw the inner and outer side of a radial is inconsequential, but I don't, especially when you factor in the tidal/step cycle that the breathing gas follows in a CCR powered by a set of human lungs. The flow of the gas is nowhere near constant, it ebbs and flows and I think this is where the radial shines as it's asymetrical gas path interacts more favorably with the tidal cycle. During an inhale or an exhale, you have lower velocity at the begining and end and the gas will slow and actually stop before being drawn through the inhale side of the loop. And any pressure drop at all is going to affect the dwell as that exhaled gas runs out of velocity, IMHO. -Andy