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Re: CO2 Calculations

Jim Miller did some calculations on the longevity of 5#s of CO2:

> I spent some time researching CO2 stuff yesterday.  One gram of
> liquid CO2
> produces 30.5cu.in. of CO2 gas at standard temperature and pressure. 
> A 1/8"
> diameter bubble is about .001cu.in. and at 1bps you use 86.4 cu.in.
> (stp) of
> gas in 24hrs.
> 
> A fully filled 5# (2270gm) tank of LCO2 should be capable of
> producing
> 69235cu.in. of CO2 gas. Note that these bottles are filled by net
> weight so
> 5# means a 5# net increase from empty to full if properly filled.
> 
> At 86.4cu.in. per day this should last 800 days. What's wrong with
> this
> picture?  I haven't seen anyone claim 2+ years on a 5# bottle.
> 
> Some ideas:  no one really bubbles at 1bps, bubbles must be much
> bigger,
> significant leaks are pretty common, improper fills shortchanging
> customers...

Have you done a sensitivity analysis on your variables?  One of the
problems with counting bubbles instead of measuring CO2 levels is that
not all bubbles are equal.  So, I suspect you are right about bubble
size being one thing that can account for inconsistency between the
calculated and actual results.  

Full fills are easy to test, since it is simply the net weight.  But I
have been shorted a half pound or so a time or two.

As for leaks.  One would expect those with the purportedly leaking
vinyl and silicone tubing to have substantially different refill
longevity than those using the "low loss" tubing.  But I submit that
that those differences are very small especially compared to the kind
of longevity your calculations predict.

So I'm putting my money on bubble size.  

Are you calculating the amount of CO2 in a bubble based on a bubble at
standard atmospheric pressure?  My bubble counter is before the check
valve, so the bubbles I count are not at room pressure but something
higher.  If the bubble is released low in the water column, there is
more pressure, making for a more compact bubble.  If you factor in
these aditional variables, and we can probalby think up a few more like
them, I think you'll find the rest of the CO2.

Scott H.

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