temperature drop in first stage...

[will_tekkie]

Hi friends...wondering some values related to the scuba gear (temp used for tank volume calculations) a question comes to my mind....what is the range or magnitude order of temperature drop once the mix is expanded in the first stage ( Tmean/Ttank)....????....i don´t know if someone else out there know something about this fact....obviously the temps ratio depends of several factors (expantion ratio, inicial conditions of temp, humity in the mix, heat transfer, etc)..but i don´t know the common values found in real situations...obvioulsly a adiabatic expansion is not a good assumption in this case....

 

[donacheson]

Hi friends...wondering some values related to the scuba gear (temp used for tank volume calculations) a question comes to my mind....what is the range or magnitude order of temperature drop once the mix is expanded in the first stage ( Tmean/Ttank)....????....i don´t know if someone else out there know something about this fact....obviously the temps ratio depends of several factors (expantion ratio, inicial conditions of temp, humity in the mix, heat transfer, etc)..but i don´t know the common values found in real situations...obvioulsly a adiabatic expansion is not a good assumption in this case....

Expansion ratio and heat transfer from the regulator parts are probably the key parameters. Good values of the temperature drop would have to based on measurement, not theory, and might well vary significantly from regulator to regulator.

 

[will_tekkie]

Expansion ratio and heat transfer from the regulator parts are probably the key parameters. Good values of the temperature drop would have to based on measurement, not theory, and might well vary significantly from regulator to regulator.

i´m agree....but what are the values we can talk about?...i´m also sure the heat transfer HAVE to be different from one to other because the mechanical design (piston with small or huge openings, diaphragm), materials (brass, titanium, etc), thermal insulation (Dry insulated system stages, dry caps, liquid filled),fins (like mk25AFfirst stage or atx200 second) , etc are also different..but ...somebody know the average values that we can find, for example in a simple non balanced piston reg?..what values are more or less found after air is expanded?..considering we breath cold air while diving the understanding of these values can be a interesting point to know.....i understand these values are not easily to get..but maybe someone knows it...

 

[WarmWaterDiver]

will_tekkie,

Here's a thread from a while back on this topic.

http://scubaboard.com/t47081.html

Page 4 of this thread is where I supplied some thrmodynamic data. The data I ran was for bone dry air as the gas composition. If you have a specific set of data you want to check, just PM me with the gas composition (%O2/%N2/%He), any other materials in the breathing gas (ppm H2O, etc.), water depth, first stage inlet (tank) pressure, and first stage outlet pressure (either metric or US units - I can convert between them).

Hope this helps.

 

[WarmWaterDiver]

Found another link Pufferfish had in a different thread too.

http://scilib.ucsd.edu/sio/nsf/diving/nedu.html

 

[pufferfish]

Hi Warmwater,

Here we are approaching the first day of summer and we are still talking about freeze failures. Up here at depth we have just cracked the 10 C mark so I can put the British North Sea Apeks reg away and use that Italian warmwater Scubapro MK25AF again

Here is a link with some info WT might be looking for.
http://www.nitroxdiver.com/Library/coldreg.html

 

[WarmWaterDiver]

Hey Puffer - thanks for the link to another cool & informative article!

It was long-sleeve shirt weather here for me this morning south of you (what am I still doing here?) - but I had 8 days in Bonaire & 7 days in Curacao last month to do some warm water diving, so my mental health is improved versus earlier this year. Still catching up on stuff that piled up during vacation to look at local water temperatures, but I'm sure they're not much higher than your area.

I added a bubble deflector to my Scubapro G500 (I ordered from the UK) - and really liked it on this trip. Gave me the exhaust bubble routing like my old Sherwood Maximus, but with effortless DRY breathing (I used my MK 20 first stage). You might consider one for your S600.

 

[will_tekkie]

Hi Warmwater,

Here is a link with some info WT might be looking for.
http://www.nitroxdiver.com/Library/coldreg.html

Hi Puffer...Very good info...exactly the one we´re talking about...Sometimes we can not imagine some things like the temp delivered by a scuba reg... :11:

considering the values given in the article for warm water (water temps here in spain are getting close to 24C or 75F ) we can estimate the heat transfer (at least for the reg. tested in the article) close to 28 KJ/Kg (12 BTU/lb). as said, the temp drop is quite linear (temp drop 28K)..therefore, the heat transfer roughly constant if we consider the other values given...

Again...Very good info...

thanks..

 

[will_tekkie]

Hey Puffer - thanks for the link to another cool & informative article!

I added a bubble deflector to my Scubapro G500 (I ordered from the UK) - and really liked it on this trip. Gave me the exhaust bubble routing like my old Sherwood Maximus, but with effortless DRY breathing (I used my MK 20 first stage). You might consider one for your S600.

Hi warmdiver...I´ve seen this deflector at internet...what´s your feedback?..is it too bulky as appears to be from the SP website? or is its dimension well designed?..if you have a picture installed can you show it to us?..i´m interested to buy something like this for a gift to my girlfriend..she likes the UW Photography...

 

[donacheson]

i´m agree....but what are the values we can talk about?...i´m also sure the heat transfer HAVE to be different from one to other because the mechanical design (piston with small or huge openings, diaphragm), materials (brass, titanium, etc), thermal insulation (Dry insulated system stages, dry caps, liquid filled),fins (like mk25AFfirst stage or atx200 second) , etc are also different..but ...somebody know the average values that we can find, for example in a simple non balanced piston reg?..what values are more or less found after air is expanded?..considering we breath cold air while diving the understanding of these values can be a interesting point to know.....i understand these values are not easily to get..but maybe someone knows it...

In my earlier message, I forgot to mention flow rate as a major variable.

In any case, I suspect that by the time the air has flowed through the first stage and the hose leading to the second stage, the temperature has returned very nearly to that of the water, so it would be the expansion in the second stage that would cool the air being breathed.

As I recall, most second stages operate with an input pressure about 100 psi more than ambient, so a calculation can be made of a typical adiabatic temperature drop in a second stage. Since T1/T2=(P1/P2)^0.286 (both teperatures and pressures are absolute), the adiabatic temperature drop in 33 feet of 68F sea water would be about 180F and in 100 feet of 68F sea water, about 130F. Obviously, we don't breath air chilled that much, so the transfer of heat within the second stage is very important - and difficult to estimate theoretically, thus requiring measurement.