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RE: CO2 Calculations

Jim Miller wrote:

>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
>diameter bubble is about .001cu.in. and at 1bps you use 86.4 cu.in. (stp)
>gas in 24hrs.

I have a calibrated flow meter with metering valve (in place of a bubble
counter and leak valve.)  I measure 1 bubble/sec to correspond to 5 mL/min,
considerably higher than .001 "cubic inch/sec."  This is independent of the
regulator pressure, but may depend on the tubing size, which in my case is
1/4" O.D. 3/16" I.D.  5 mL/min is 7200 mL/day

>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.

Right, 1 gm CO2 produces 512 mL at STP.  A 5#(2270 gm) tank produces
1,162,240 mL.

>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.

At 7200 mL/day, a 5# tank should last 160 days.

>Some ideas:  no one really bubbles at 1bps, bubbles must be much bigger,
>significant leaks are pretty common, improper fills shortchanging

I think, for many systems, most CO2 injected into the aquarium is lost due
to inefficient mixing with the water.  Most injected CO2 reaches the water
surface as bubbles and is lost into the atmosphere.  Furthermore, a lot of
the CO2 dissolved into the water is not absorbed by plants, but lost at the
water surface, and this is increased by surface disturbance from water
movement.  I think silicone tubing losses ~10% percent of the CO2 that
passes through it at typical aquarium pressures, flow rates, and tubing

If our goal is a mini CO2 system for small (2-12 gal) tanks, with a cheap,
small bottle that lasts a long time, I think we need 1) a 100% efficient CO2
diffuser/reactor, 2) minimal surface disturbance (maybe a covered tank would
help), and 3) spend the extra $2 for CO2 resistance tubing.

Joe K

mL = milli-liter.  Go metric and S.I.!