Design of tiny CO2 cartridge.

[chrysalis]

Hi all,

I am at the earliest stage of a potential invention. Perhaps, the most important component would be a tiny vessel which must supply circa 20 to 30ml of CO2 when breached, operating at temperatures of between 0 and 35 degrees centigrade and an operating pressure of ambient pressure. If I am correct in understanding that CO2 has a critical temperature of around 31 degrees centigrade where the pressures increase dramatically then I could potentially re-define the operating temperature to withing a few degrees less of that maximum.

The rate at which the gas is expelled may be a lesser issue.

The size of the vessel is important for the overall design of the invention. The shape may be important too, if the diameter of the vessel were too great.

Optimally as small a vessel as 'practicable'.

Could anyone give an opinion on the minimum size of vessel which could be used?

Could anyone give an opinion on whether such a vessel could be manufactured?

Could anyone give an opinion on the thickness of steel or aluminum that might be used or has anyone any other suggestions for materials?

Could anyone give an opinion on anything that they might consider relevant or important?

Could anyone speculate for example on the manufacturing difficulties that might be involved?

Could anyone speculate on likelihood that such a component could be mass produced for cents or even fractions of cents?

Regards and many thanks for any consideration.

Chris

[Kelly_Bramble]

Search the internet for "Stop & Go Tire Repair Replacement CO2 Canister Harley".

Small Co2 canisters are readily available .

[chrysalis]

Hi Kelly,

I am aware of these canisters and many like them, the smallest I have found is 0.375 inches in diameter and 1 inch in length holding 0.75 grams of CO2. I think the canister you have pointed out comes in at around 16 grams of CO2 within.

I may not have made it clear enough in my explanation, that I need to contain, only enough CO2 to expand into around 20-30 milliliters at standard pressure and within the temperature ranges I mentioned.

I am not exactly sure what volume the container should optimally be, to hold such a minute amount of CO2 but those canisters available for tyre inflation, airsoft guns, soda streams, keyboard blowers, life preservers etc hold usually between 8g and 16g of CO2. I would expect to hold somewhere in the region of between 0.1g and 0.05g in my notional canister. I may be incorrect in the gram requirement but it will not be far from that.

Regards

[Kelly_Bramble]

The storage volume for a compressed gas can be calculated using Boyle's Law:

p_a V_a = p_c V_c

where
p_a = atmospheric pressure (14.7 psia, 101.325 kPa)
V_a = volume of the gas at atmospheric pressure (cubic feet, cubic meter)
p_c = compressed pressure (psi, kPa)
V_c = volume of the gas at compressed pressure (cubic feet, cubic meter)

Volume of free gas in a Storage Volume

The amount of free gas at atmospheric pressure in a given volume as a cylinder storage can be calculated my modifying (1) as:

V_a = p_c V_c / p_a

Gas can be stored in high-pressure cylinders ranging to 6000 psig (410 bar), normal-pressure cylinders ranging between 2000 and 2500 psig (140 and 175 bar) and low-pressure cylinders ranging up to 480 psig (34 bar).

[chrysalis]

Hi again Kelly,

Are you able to do the math for me and attempt to answer any of the questions I asked in my initial post?

Really it is the potential size I can shrink the canister to I am mostly interested in . I do not expect a highly technical outline of solutions to my issues, if only someone on the forum would be bold enough to stick their neck out and offer even some ball park guesstimates.

Imagine you were talking to one of your family members or a (not incredibly technical) friend at dinner and they were speculating on the minimum size of a canister or cartridge.

You see, it is for the purposes of attempting to determine (at the early stages of an invention idea) whether a component in an invention could likely exist and be made cheaply.

If I were reasonably convinced of this, then I could move on with larger scale prototyping stages, while planning more formal investigations about creating such a small scale cartridge.

I am aware that there is sometimes a certain reluctance in forums (fora?) to do someones homework for them and to a degree this is what I am asking but not to any level of accuracy as to create a final product by any means. I am asking after the expertise and experience I assume exists within members of this forum, I need the engineers edge. If questions such as mine are not welcome, as I am not as technically knowledgeable or I am an inexperienced would be inventor type then please excuse me and prompt me accordingly.

Thanks for listening.....

[chrysalis]

Can I ask then. Generally with gas cartridges/canisters designed to hold CO2 or Propane, is the size and wall thickness of the vessel directly proportional to the volume requirement?

[Cragyon]

Can I ask then. Generally with gas cartridges/canisters designed to hold CO2 or Propane, is the size and wall thickness of the vessel directly proportional to the volume requirement?

Generally, yes....

[chrysalis]

Am I correct in understanding that CO2 in liquid state will be under pressure of over 800psi? At SATP.

If dimensions were generally, directly proportional, then a tiny 0.5 gram cylinder of liquid CO2 would have rather thin walls compared to say the 16gram standard types. Could these thinner walls withstand the same pressures of at least 800psi?

[chrysalis]

Thank you Cragyon.

[roineust]

Hello chrysalis!

As part of an artistic project, i am building a small robot for painting little air brush style stencils on walls. The bot runs along a room and paints/sprays changing stencils on lower parts of walls.

The robot uses a set of quite small servos, so the air bruh i am trying to build for it to carry, has to be small as well. I am looking for this purpose, for an off the shelf CO2 cartridge, that weighs 10-20 grams at most (the cartridge with the gas inside, not only the gas).

After finding this thread here, i got under the impression, that maybe you could refer me to a link, where i can easily buy such sub-micro CO2 cartridges.

Would that be possible?

Thanks a lot!