WOB Air Vs. Helium

Dive!Dive! · 22nd April 2008, 19:13

Folks
There has been much (interesting and iluminating) discussion regarding WOB on other threads recently.
I have a general question on this topic : All of the tests are done on Air at 40m depth as far as I know ?
Lets say we have a result of 3J/L on Air. What would be the impact of using, say, 18/45 as dill, also at 40m ? What could you reasonably expect for 18/45 as say 80m depth?
I'm not seeking absolutes, just a general feel for what difference it makes.
Any thoughts ?
Cheers
Steve

Ferg3333 · 22nd April 2008, 22:46

there are also the trimix and heliox tests done by ap???

**nigelh** · 23rd April 2008, 08:01

As I understand it WOB depends on viscosity and density and helium is right down on density but up on viscosity.

I know of some medical tests at 1 bar where substituting 22/78 for air reduced the WOB 21% in some tests and 15% in others so I decided it probably wasn't enough of a change to worry about.

If anybody can point me to some proper work on this subject I would be quite interested. The real nasty problem is that in a system like the lungs our concepts of gas flow in terms of Reynolds numbers just falls to bits.

paulraymaekers · 23rd April 2008, 09:00

Quote: (Originally Posted by nigelh)

As I understand it WOB depends on viscosity and density and helium is right down on density but up on viscosity.

I know of some medical tests at 1 bar where substituting 22/78 for air reduced the WOB 21% in some tests and 15% in others so I decided it probably wasn't enough of a change to worry about.

If anybody can point me to some proper work on this subject I would be quite interested. The real nasty problem is that in a system like the lungs our concepts of gas flow in terms of Reynolds numbers just falls to bits.

from what I heard: for the CE test it is more difficult to pass with air at 40 meter, then with 10/90 at 100m

regards
paul

**nigelh** · 23rd April 2008, 10:27

Quote: (Originally Posted by paulraymaekers)

from what I heard: for the CE test it is more difficult to pass with air at 40 meter, then with 10/90 at 100m

I admit I was thinking more in terms of WOB in terms of total labour expended so the lungs are part of the equation rather than the CE style tests where just the outside plumbing is considered.

paulraymaekers · 23rd April 2008, 12:12

Quote: (Originally Posted by nigelh)

I admit I was thinking more in terms of WOB in terms of total labour expended so the lungs are part of the equation rather than the CE style tests where just the outside plumbing is considered.

as far as I understoud, it works in the same way if you include your lungs

paul

Dive!Dive! · 23rd April 2008, 12:31

Paul
Interesting comment on the 10/90.
Subjectively I know it must be better from OC experience. Give that the cost of He for CCR diving is tiny compared to OC and given the importance of low WOB from a CO2 viewpoint, there must be an argument for always having some He in the Dill (I realise there are other considerations re the use of He...)
Still, it would be nice to see back to back Air vs Mix under the std 40m test conditions.

Re the earlier post - where is the AP data ?
Thanks
Steve

Ferg3333 · 23rd April 2008, 12:52

I dunno if its publically available but the unit is tested and approved for mix so it must be somewhere

22nd April 2008, 19:13	#1 (permalink)
Dive!Dive! New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2006 Location: Somerset, UK Posts: 90	WOB Air Vs. Helium Folks There has been much (interesting and iluminating) discussion regarding WOB on other threads recently. I have a general question on this topic : All of the tests are done on Air at 40m depth as far as I know ? Lets say we have a result of 3J/L on Air. What would be the impact of using, say, 18/45 as dill, also at 40m ? What could you reasonably expect for 18/45 as say 80m depth? I'm not seeking absolutes, just a general feel for what difference it makes. Any thoughts ? Cheers Steve
(Online)

22nd April 2008, 22:46	#2 (permalink)
Ferg3333 Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2007 Location: Blackpool Posts: 114	Re: WOB Air Vs. Helium there are also the trimix and heliox tests done by ap???
(Offline)

23rd April 2008, 08:01	#3 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 784	Re: WOB Air Vs. Helium As I understand it WOB depends on viscosity and density and helium is right down on density but up on viscosity. I know of some medical tests at 1 bar where substituting 22/78 for air reduced the WOB 21% in some tests and 15% in others so I decided it probably wasn't enough of a change to worry about. If anybody can point me to some proper work on this subject I would be quite interested. The real nasty problem is that in a system like the lungs our concepts of gas flow in terms of Reynolds numbers just falls to bits. __________________ nigelh
(Online)

23rd April 2008, 09:00	#4 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,344	Re: WOB Air Vs. Helium Quote: (Originally Posted by nigelh) As I understand it WOB depends on viscosity and density and helium is right down on density but up on viscosity. I know of some medical tests at 1 bar where substituting 22/78 for air reduced the WOB 21% in some tests and 15% in others so I decided it probably wasn't enough of a change to worry about. If anybody can point me to some proper work on this subject I would be quite interested. The real nasty problem is that in a system like the lungs our concepts of gas flow in terms of Reynolds numbers just falls to bits. from what I heard: for the CE test it is more difficult to pass with air at 40 meter, then with 10/90 at 100m regards paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
(Online)

23rd April 2008, 10:27	#5 (permalink)
nigelh New Member Current Rebreather/s: Inspiration Vision Other CCR Other Rebreather/s: Inspiration Classic Other CCR Join Date: Mar 2005 Location: Brighton, Sussex, UK Posts: 784	Re: WOB Air Vs. Helium Quote: (Originally Posted by paulraymaekers) from what I heard: for the CE test it is more difficult to pass with air at 40 meter, then with 10/90 at 100m I admit I was thinking more in terms of WOB in terms of total labour expended so the lungs are part of the equation rather than the CE style tests where just the outside plumbing is considered. __________________ nigelh
(Online)

23rd April 2008, 12:12	#6 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,344	Re: WOB Air Vs. Helium Quote: (Originally Posted by nigelh) I admit I was thinking more in terms of WOB in terms of total labour expended so the lungs are part of the equation rather than the CE style tests where just the outside plumbing is considered. as far as I understoud, it works in the same way if you include your lungs paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
(Online)

23rd April 2008, 12:31	#7 (permalink)
Dive!Dive! New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2006 Location: Somerset, UK Posts: 90	Re: WOB Air Vs. Helium Paul Interesting comment on the 10/90. Subjectively I know it must be better from OC experience. Give that the cost of He for CCR diving is tiny compared to OC and given the importance of low WOB from a CO2 viewpoint, there must be an argument for always having some He in the Dill (I realise there are other considerations re the use of He...) Still, it would be nice to see back to back Air vs Mix under the std 40m test conditions. Re the earlier post - where is the AP data ? Thanks Steve
(Online)

23rd April 2008, 12:52	#8 (permalink)
Ferg3333 Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2007 Location: Blackpool Posts: 114	Re: WOB Air Vs. Helium I dunno if its publically available but the unit is tested and approved for mix so it must be somewhere
(Offline)

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