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Jim, Have you ever analysed your mix immediatly after mixing? I have noticed a difference (especially with hi O2 mixes) so I wait (I will not roll a tank as there is no mechanism to force turbulance inside the tank, waste of time). I would rather wait and get a correct reading the first time than try to figure out how soon after mixing I can measure. Steve -----Original Message----- From: Jim Cobb [mailto:cobber@ci*.co*] Sent: Friday, April 09, 1999 8:25 AM To: Steve Hogan; pdisler@io*.ne*; silent@cu*.ne* Cc: Tech Diver Subject: RE: Trimix Question I really have a hard time getting my brain wrapped around this stratification thing. When you are adding gas to a cylinder it not like you are decanting it in like you are mixing a black and tan. You are blasting high pressure gas through a tiny oriface in a violent fashion into your tank and the goddamn molecules are flying all over the fucking place. They hardly have a chance to delicately float down like a bunch of snowflakes into a nice stack of different gas densities. When you are in a fire what do you do to avoid the smoke? Crawl on the floor. The smoke/air mixture is up on the ceiling because of its temperature, not because the house is not being rolled. As the temperatures mix and even out the smoke is more than happy to fill the room top to bottom. This rolling tank BS is an old wifes tail and cannot be explained via physics. The inside of a tank is smooth, there are no vanes sticking out to "mix" the gases, so how could rolling possibly help? The temp differences do not have to be measured in 100's of degress for inversion layers to take place but eventually the temps even out and you get a good mix measurement. You don't have to roll the goddamn tanks. Can't you knuckleheads see this? Jim Sender: Steve Hogan Date: 4/8/99 8:17 PM >Jim, > >Since I fill the cylinders slowly there is not much heating going >on. I suppose you could test this by doing a fast fill (with the O2) >and let us know. If we don't here from you we will pretty much know >what happened (wink). > >If temperature were an issue then warming a tank after there is a known >good mix should throw off the measurement. I always measure my mixes >in my garage (my safe haven) so it is a bit on the cold side. I >do not wait until I am on the boat to check the mix (that comes under >the heading of preparation). > >Comments. > >Regards > >Steve > >-----Original Message----- >From: Jim Cobb [mailto:cobber@ci*.co*] >Sent: Thursday, April 08, 1999 4:55 PM >To: Steve Hogan; pdisler@io*.ne*; silent@cu*.ne* >Cc: Tech Diver >Subject: RE: Trimix Question > > >I don't know about you guys but I think the problem we are dealing with >here is the temperature of the mix rather than stratification. As the mix >cools off the reading becomes more accurate. > > Jim > >Sender: Steve Hogan Date: 4/8/99 6:53 PM > >> >>I have run into this and have modified my mixing procedures >>so that after I add the O2 to the helium I wait 1 day (I >>usually mix at night so waiting around is not appealing) >>before measuring the O2 % (O2 & He). It is not hard to figure >>out what percentage I expect after mixing O2 with He. >>Next step is to add air, wait a few hours (usually doing >>something else) and then measure again. >>I fill about 50 psi/min so I expect to not get much mixing from >>Brownian motion. >> >>Steve >> >>-----Original Message----- >>From: Patricia Disler [mailto:pdisler@io*.ne*] >>Sent: Friday, April 09, 1999 1:14 PM >>To: S I L E N T I M M E R S I O N >>Cc: techdiver@aquanaut.com >>Subject: Re: Trimix Question >> >> >> >> >> >>At 09:16 AM 4/8/99 -0700, you wrote: >>>Frank, >>> >>>>Not me, but I do let the filled tanks rest a day before analyzing. An if >>>>you want to tell me >>>>thats not neseccary I recommend that you try this: Fill oxygen, top with >>>>air, wait a minute, >>>>analyze mix, turn the tank so that the valve faces ground, wait another >>>>minute and than >>>>re-analyze the mix. >>> >>>And it's the same... or not? >>>When filling a tank the temperature and pressure are high which in turn >>>gives a high diffusion coefficient. Makes the mix homogeneous almost >>>instantaneoulsy (couple of seconds). >>>What kind of differences do you get? >>>What kind of analyser do you use, are you sure the hoses are drained when >>>using a regulator or something? >>> >>>Regards,> >>>THOMAS >> >>I have witnessed Nitrox mixtures take a while to fully homogenize. Several >>years ago while mixing 80/20, (Yeah I know don't start) it came out 63% O2 >>approx 30 min after the very s-l-o-w top off to fill pressure. Yes I >>checked the calibration of the aynalizer (Teledyne TD-50). Each time I >>would check the O2 reading would climb. I did this over a period of several >>hours. Later it was right on 80%. >>I'd have to say stratification can and does occur, esp. if there is not >>enough turbulence during top off. >>I have never seen this with Trimix as the fill rates are much higher. >>However I suppose it could occur if they too were topped slowly. >>At any rate I never seem to dive my gas until they show the correct >mixture. >> >> >> >>"SILT HAPPENS"JD JEFF DISLER >> SAFE CAVING NSS 26000 >>-- >>Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. >>Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. >>-- >>Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. >>Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. >> > > > ------------------------------------------------------------------- > Learn About Trimix at http://www.cisatlantic.com/trimix/trimix.html > >-- >Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. >Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > ------------------------------------------------------------------- Learn About Trimix at http://www.cisatlantic.com/trimix/trimix.html -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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