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Old 04-23-2014, 07:53 PM   #1763 (permalink)
Echo
Mill Monkey
 
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Join Date: Jan 2009
Location: Orange County, California

Quote:
Originally Posted by Spider! View Post


Kind of a funky time of year to start a class, isn't it?

While you are in the neighborhood, see if you can find a temperature-entropy diagram for CO2. It's actually more thermo than heat transfer, but it can give you real heat values and you can compare them to adiabatic and isothermal values. It will tell you the total energy load for dumping a shot, but it will not tell you exactly where that energy will go, just somewhere between the 12gram and the end of the barrel (or a little beyond). We associate snow with poor efficiency, but cold muzzle blast shows that the CO2 is still picking up heat at that point.

There are good places to pick up heat transfer, and aluminum isn't far off from copper (that you will see in class). Check out stainless too, and you will see why stock automags do not perform as well as other designs for CO2. Hopefully they still cover Heilser charts; reg shape is the other sadness of the original mag and heat transfer.

Quarter system. A gift and a curse.

I've used my Thermo books tables for CO2 gas before to try and find theoretical efficiency without heat transfer (I got 276 shots). You can find how much energy is left (as enthalpy) when it expands to atmospheric temperature and pressure. Adding this to the kinetic energy of the paintball gives you most of the energy out. Then you just have 12 grams of liquid CO2 at some temperature and pressure inside the cartridge, which is just another chart lookup to find its enthalpy value. This of course is assuming complete heat transfer to the CO2 throughout the whole process.

I wouldn't know what to do with an entropy table but I'll keep my eyes and ears open.

Also an automag is what I want to bolt my solid copper pipe dream heat exchanger to.
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