How does CO2 concentration vary between DIY and Pressurised?

[tom_m2k]

Hi,

Simple question...

How does the concentration of carbon dioxide gas vary between that produced by a DIY set up (fermentation) to that from a pressurised system, with matching volumes?

For example, would 10ml of CO2 (in volume) from a DIY system contain the same number of CO2 particles as 10mls of CO2 from a pressurised CO2 bottle? ie - is it only CO2 that is given off from fermentation, or will there be other gases given off at the same time?

I ask this question assuming ideal conditions - no leaks, same tank and same diffusion technique etc...!

I know this is a simple question, but I can’t think back to my science lessons...!

 

[ceg4048]

Re: How does CO2 concentration vary between DIY and Pressuri

Hi,
One cannot really compare these two systems (or any two gas systems) from a volumetric (litre) standpoint. Gas and fluids should only be compared from a mass flow rate perspective. The summation of the individual particles add up to mass, or weight. In a given volume, the number of particles within that volume will depend on the density, pressure and temperature of the gas within the volume. The parameters determine the spacing between particles. Less space between particles in a volume means higher number of particles and therefore a higher mass (weight.)

In the case of a pressurized cylinder the CO2 is in liquid form, and it leaves the cylinder under high pressure as a gas. It's then down regulated to a working pressure. The mass of CO2 produced by the typical fermentation system is much lower and is also very uneven because it depends on organic processes.

Incidentally, you can already determine what mass of CO2 is available in a pressurized system by the mass rating of the cylinder. Presumably, a 500 gram CO2 bottle holds 500 grams of CO2. Some cheeky cylinder ratings give you the combined mass of the cylinder + gas, so for example a cylinder might have a 5Kg rating but may only have 3Kg of CO2 liquid in a 2Kg steel cylinder. Whatever the case, this will be a fixed value and so the amount of CO2 delivered per second can be calculated based on the regulator exit pressure and the orifice/tube diameter. In a fermentation system one doesn't know the total amount of CO2 that will be generated beforehand, but a mass flow rate can be calculated assuming a regulator is attached and the pressure and tube diameter is known. Since the pressure varies as a function of yeast activity, then the mass flow rate will vary as well.

In general though, pressurized cylinders of any significant size will deliver a much higher mass flow rate and for a longer and more consistent basis over time than a fermentation system. A much better value overall.

Cheers,

 

[tom_m2k]

Re: How does CO2 concentration vary between DIY and Pressuri

...A simple question does not always produce a simple answer!

I was not expecting such an indepth answer - interesting none the less!

Thank you, you seem to be a valuable resourse to this forum!

 

[mattyc]

Re: How does CO2 concentration vary between DIY and Pressuri

i agree with ceg4048, you would need to look at fluid dynamics (gasses are fluids) to calculate the flow rates of the pressurised system. i have just been working on a project that uses mass flow rates of gasses through pipes this stuff gets verry complex with compressible flows but it can be worked out. a biolagist could probably come up wuth a figure for the amount of co2 produced by the bacteria.

under idealised conditions and equal flow rates both systems would provide the same gas saturation in the water, but the conditions are far from ideal and therefore the bacteria will provide an unstable supply of gas.

The stablity is what we want and that is why we use a presurised system.