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Re: CO2 diffuser

Scheele Juergen wrote:

> I am remember an artikel a while ago about difusing CO2
> through an atomizer in the tank.
> The author mentioned that as soon as CO2 has left the
> diffuser (atomizer) it is already dissolved in the water !?!

I think this is most of the way right.  There would still be some CO2
left in the bubble, though.

What follows is probably something that none of us actually need to

Some time ago I put together a mathematical model to describe the
diffusion of CO2 out of a bubble and of other gasses into the bubble.  I
did the same thing to describe the diffusion of gasses in and out of a
bell diffuser.

The pressure inside one of those tiny bubbles is higher than the
pressure in the water around it because of the surface tension on the
bubble.  The smaller the bubble, the higher the pressure gets.

There is an initial flux of CO2 out of the bubble and a smaller amount
of gas from the water into the bubble, with a net reduction in the
volume of the bubble.  At some point as the bubble shinks, the pressure
inside the bubble reaches the point where gases can no longer diffuse
into the bubble.  Simultaneously, the diffusion of CO2 out of the bubble
accelerates.  The bubble eventually implodes.  The whole course of
events takes place in seconds - sometimes a few seconds.

There were two conclusions from that model.  First was that the bubbles
really need to start out very small or quite a bit of gas will probably
get wasted.  Second was that yeast-generated CO2 (saturated with water
vapor) takes a little longer to dissolve than dry CO2 from a bottle.  If
I remember right, the "wet" CO2 took about 10% longer then the dry CO2.
Results on the bell diffusers (and some experience with bell diffusers)
encouraged me not to use them.  If you want to use a bell diffuser, then
probably you will get the best efficiency using them to dose batches of
CO2 instead of bubbling CO2 into it continuously.  Add a dose of CO2 to
the bell and let it dissolve, then add another dose and wait, and so
on.  If you add CO2 continuously then gasses from the water build up in
the bell and slow down the rate of CO2 diffusion out.  It doesn't take
very long before the diffusion rate drops below the rate that CO2 is
continuously added and then the bell starts burping.  CO2 gets wasted. 
There's quite a few variables in that conclusion, so your mileage may

Roger Miller