Thermal Aspects of OC Regulators : The Air we breath

[CG43]

Hello

The old EU standard EN 250 allows 3 joules/liter of breathing work.
A diver who breathes 25 liters in 1 min. thus performs 3J/L *25 L/60 sec. = 1.25 watts.
Cycling at medium speed needs about 100 watts , that's 80 times more .
So how important is the breath work that the reg. causes? .
Modern regs. have 1/4 of this breathing work but may be some one needs 100 L/min. air.

Now the question is how much does a diver do to warm up the air cooled by the expansion (Joule/Tomson effect)
and how much power does it take to dam water because the air from the tank is extremely dry.
Karrl's Rebreather page give us some nummbers of how many watts a diver needs .

Thermal Aspects of Rebreather-Design

The first line "-10°C regulator are unfortunately our modern regs. with plastic second-stage .
The thermal power required is about 100 times as great as the breathing work required by the reg.
and is about the same as cycling. In addition, the dry air dehydrates us .

What can be done ?
1.)Because most of the cooling happens in the first stage,
an IP/water heat exchanger between the first and second stages makes sense. Approx. 2m of stainless steel pipe is enough for a significant heating of the air.
For the professionals, a long supply hose also does. From the "Kirby Morgan" company there is also the tube heat exchanger obtainabel.

2.)Low pressure heat exchanger and humidity recovery.
Unfortunately, only the mouthpiece housing is suitable for the single-hose reg.
As far as I know, Sherwood has or had heating plates in plastic second stages.
Unfortunately I could not find about it now, but surely someone can show it here.

3.) The doubelhose reg.
Last winter I did a 1 hour dive in a wetsuit. After that I was really frozen.
3 days later, exactly the same conditions only instead of a single-hose regulator a doubelhose was almost comfortable .

At the moment the diving industry provides us with comfortable to breathe regs.
It is our business to make it clear that we the buyers also want a comfortable air , not colder and not drier than necessary .

 

[Mobulai]

Oh is that why DH regs are nice fir cold diving? Cuz they have lower flowrates without lowering the cracking effort so the gas coming in aint as cold?
(Not rhetorical, I’m just extrapolating, haven’t tried a DH yet)

 

[CG43]

Hello Mobulai

The cooling depends on the type of gas , the tank pressure, the depth and how much gas you breathe.
This has nothing to do with the type of reg.
But a doubelhose reg.with a large metal housing and a long, ribbed pleated hose through which the breathing gas flows turbolent supplies considerable amounts of heat from the surrounding
water to the breathing gas.

- Mono

 

[halocline]

Oh is that why DH regs are nice fir cold diving? Cuz they have lower flowrates without lowering the cracking effort so the gas coming in aint as cold?
(Not rhetorical, I’m just extrapolating, haven’t tried a DH yet)

DH regs have a much larger volume of ambient pressure air than do single hose regs. As such, the breathing air expands from IP to ambient much further away from your mouth and has time to warm up before making it into your lungs. It has nothing to do with flow rates.

 

[halocline]

Regarding cold-dry vs warm-moist breathing air and how regulator set up can affect things, I would say that this is one of the reasons I use old SP metal 2nd stages in cave diving. The heat exchange is more efficient in the body of the 2nd stage and there’s frequently a bit of moisture condensing in the reg from exhaling. I believe this helps to moisten the inhaled air.

I wouldn’t have any idea how to quantify that and I would have no interest in trying. I just enjoy the sensation of using these old metal 2nds on three hour dives. I might give up a bit of WOB numbers, but since I’m a human diver, not a test machine, I really couldn’t care less what the numbers are.

 

[CG43]

Hello halocline
I

Regarding cold-dry vs warm-moist breathing air and how regulator set up can affect things, I would say that this is one of the reasons I use old SP metal 2nd stages in cave diving. The heat exchange is more efficient in the body of the 2nd stage and there’s frequently a bit of moisture condensing in the reg from exhaling. I believe this helps to moisten the inhaled air.

For the same reason, I almost only use metal second stages.
In the comparison I described, an old SP MK 2 second stage. But the doubelhose is even warmer.
With regard to the required heat power for the water vapour, the doubelhose has a high savings potential due to its warm air. But this only comes into its own if the inhalation way contains moisture. Experience has shown that this is the case without valves in the mouthpiece. In this case, you will be able to reduce the 44.8W specified in Karl's rebreather page .
Long pleated hoses and mouthpieces without valves are exactly what you see in old films from
Cousteau and others where great diving is done without a diving suit .
Even though I do it on simple dives , I don't recommend these simple mouthpieces. The doubelhose with valve mouthpiece is easier and safer to dive just because no water gets into the inhalation tube.

 

[Imla]

I would assume that the regulatory value for work of breath is related more to the fysiologically higher risk of CO2 retention with following risks rather than the overheating of the regs. If you need to work hard to breathe, your respiratory rate will eventually slow down and the volume of each breath will diminish. If WOB is significantly increased, so will the risk of hypercapnia and it related risks.

 

[CG43]

Hello Imla

I would assume that the regulatory value for work of breath is related more to the fysiologically higher risk of CO2 retention with following risks rather than the overheating of the regs.

Overheating is the wrong word . Did you want to write something like overwhelm?

The air in the bottle has about water temperature and therefore cools down to below water temperature when relaxed. With the water you can only supply heat as long as the air temperature is less than the water temperature The exhaled air of the diver is about 36°C. An overheating of the reg. is therefore impossible.

What ist the true WOB and how big is the share of the Reg. ?
Today it's to late . I will continue this later .