intercooler

Marc T

Im playing with the idea of such a system placed in the inhale way to induce condensation before a sensor housing to decrease condensation on the sensors.
Any thought on the usefulness of such a thing?

Genesis

To get the condensing humidity out of the system you have to cool the gas flow and then allow it to warm back up, so that the relative humidity will be lower than 100%.

Assuming the only fluid you have available for the cooling is ambient seawater, how would you then warm it back up before the sensor block?

Its a neat idea but I'm not sure the mechanics are practical given the realities of the environment.

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Sutty

Ive wondered about this too, a couple of ideas:

1. Cool the exhale gas, let it condense out, then let the scrubber reaction warm the gas back up. Design the system to then keep the gas as warm as possible from leaving the scrubber to reaching the sensors.

2. Use a "countercurrent" system where the gas is cooled in a set area but the gas ducting to that area is in close thermal connection (eg each side of a metal barrier), arranged such that gas going to the cooled area is cooled by the gas coming back, simultaneously gas coming back from cooling is warmed by warm gas going to be cooled. Arranged properly countercurrent heat exchange can be surprisingly efficient.

Neil

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Genesis

I think the problem you're going to run into there is that the scrubber reaction liberates water vapor. This means the gas coming out of the scrubber stack will be saturated - even if the gas going in is not.

Here's an idea, although I don't know if its practical....

Pass the exhale gas axially through the scrubber from top to bottom. At the bottom, use an air/water H/E to cool the gas, condensing the moisture. Arrange to trap this (for longer dives) so you can expel it.

Now, the gas coming back to the inhale side comes up through the CENTER of the scrubber via a pipe that is made of a high-conductive material (e.g. stainless steel) and patterned to give maximum reasonable surface area. The airflow is thus heated by the scrubber's reaction heat, but does not pick up any more moisture - the relative humidity falls out of the condensing range.

The sensor block is then placed as close as possible to the exit of this area, so that the gas cannot cool down again appreciably before going out to the inhale house.

That should work but the mechanics of working the gas flow and machining to achieve it may get quite tricky, since the sensors need to have both front and back in the same gas space.

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"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
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lizardland

Wouldn't the downside of lowering the humidity be the increase in thermal loading on the body? You are going to have a dry gas hitting the lungs on every breath.

Humidifying dry breathing gas is one of the biggest energy losses (probably THE biggest) on OC, so your back in this situation, losing one of the big physiological advantages of CC. I think I'd rather stay warm and hydrated and live with the potential of condensation on the cells.

You're also needing to introduce a water trap and either some way to contain it or an offboard dump... read "failure point".

Couldn't you introduce some kind of heating element around the sensors so the surfaces will not be cold enough to condense on? But then that may screw up your readings depending on how good the temperature compensation of the cell is.

Not sure if it helps, but some firefighting Rebreather's pass the gas over a dense gel to cool it.

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Marc T

The simplist "idea" was to temporary localy increase condensation with the "hope" it will decrease it just after in a , for example, well insulated sensors housing.
Of course the final result for the breathed gas moisture dont change.
The thermal balance sheet cant be changed if you dont add or extract energy ( in a chimical or electrical or mechanical way) so the global condensation level will be the same in the whole system, you just try to manage it in the best place.
Im I wrong following these idea?