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>>Posted on 27 Oct 1995 at 19:59:53 by Christopher M. Parrett >>Gas Blending > >>One of THE most requested tools in Abyss is a gas mixing system that does >>not rely on Partial pressure blending techniques. People are asking me to >>lay out a controlled proceedure to increase the likihood of being close to >>the mark on the first fill. As no one else has done this before, and I can't >>find it anywhere else myself, we decided to take it on a year ago. Much to >>my surprise it has been extremely difficult to get the math to reflect >>reality. With that in mind I decided to get as large a sample of real world >>mixes as I could to use as a baseline for compensation. > >I assume the math is fine and that it is your models of >the processes that involve the creation and exchange of heat >that causes you trouble. > >If the processes you are modeling are not reversible in the >thermoodynamic sense you sit there with unequalities and not >mathematical equalities. > >I'd think you could push through most of this but I fear the user >would have to input a large number of variables to get this >machinery to output numbers close to target: >type of tank (incl. material, thickness of walls) >cooling bath (how high up is it on the tank, what's it's temperature, >volume, rate of renewal), rates of gas transfer, heat transfer >etc etc ad infinitum. > >So I do wonder how far you can push the code and expect >good results without scaring people off with an excessive >number of input parameters ? > >john There is no doubt in my mind that we WILL run into limitations. What my goal is, is to allow the user to choose from an inventory of cylinders (we have about 100 now). This inventory has all of the data we need for the math. He then specifies, Dry fill or wet, if wet chilled or ambient. What the final fill pressure is. What the final Gas percentages are. We then give him a fill sequence, by time and by pressure. Assuming he is able to follow it, we "Should" be able to get fairly close to what he wants. Perfect, probably not, close, probably so. And importantly, this type of math will accomodate high pressure fills to 300bar+, where PP blending really begins to fall apart. Christopher M. Parrett, President, Abysmal Diving Inc. Makers of ABYSS, Advanced Dive Planning Software. 6595 Odell Place, Suite G. Boulder CO, 80301 Ph, 303-530-7248, Fx, 303-530-2808 ftp://abysmal.com/users/abysmal http://www.emi.net/gulfstream/abyss/abyss.html
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