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At 12:08 AM 4/9/99 +0200, Hans Petter Roverud wrote:
>I know it shouldn't happen but it does:
>
>Some mixes take time to mix properly unless you roll the cylinders or turn
>them upside down a few times.
This thread got me thinking about why the gasses in a cylinder
might not mix thoroughly during the filling process and I
came up with an interesting result. If you find an error,
please be gentle with me... it's late as I write this. 8-)
Viscosity is usually measured in the SI unit poiseuille with
dimension of newtons*sec/m^2. I looked up the numbers,
plugged them in and got 1.0*10^-2 for water and 1.8*10^-5 for
air. Then, I multiplied the figure for the viscosity of air
by 238 (~[3500/14.7] the number of atmospheres at 3000 PSI)
and got 4.3*10^-3. So, we have:
Water = 10.00 millipoiseuille
Air at 3500 PSI = 4.32 millipoiseuille
That means (if I didn't mess up) that, while air at sea level
pressure is one tenth of one percent the viscosity of water,
pressurized air at 3500 PSI is over 43% as viscous as water;
that's pretty thick. No wonder it doesn't mix well on its
own.
BTW, one very interesting thing about viscosity is that,
with increasing temperature, viscosity decreases in
liquids, but increases in gases. All the more reason
to fill slowly.
-Mike Rodriguez
<mikey@ma*.co*>
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