CO2 / N2 Mixed Gas Behavior Question

[MMcCawley]

I'm working on an application that utilizes liquified CO2 (at vapor pressure) to act on a hydraulic bladder (similar to an accumulator) with the goal of providing a constant pressure as the volume of oil in the bladder fluctuates. The device operates in a 17-26C environment creating fluctuation in vapor pressure of ~20% which is undesirable. I ran a test using a 75% N2 / 25% CO2 mix which significantly reduced the pressure fluctuation at these temperature extremes.

My question is, will the N2 / CO2 mixed gas act like a traditional gas (pressure drops when volume increases), liquified gas (constant pressure when liquid exists) or as a hybrid of the two?
If the latter, would there be an optimum mix ratio to deliver near constant pressure with varying volume while minimizing temperature related effects?

Thanks for your time.

 

[BigInch]

The more N2 you have, the more it would be expected to behave more like a perfect gas, as long as you stay at relatively similar temperatures and pressures where compressibility of both gases remain relatively negligable.

I don't think there is an optimum, rather more a linerly proportionally determined point where you have still acceptable performance.

You could achieve similar results by increasing the size of the vessel containing the bladder. A given change in bladder volume would produce a lesser change in the vessel's pressure as the vessel's volume increases.

Learn from the mistakes of others. You don't have time to make them all yourself.

 

[MMcCawley]

Thanks for your reply BigInch. I agree, I could achieve similar results by running a large amount of straight N2 thus minimizing the change in volume but unfortunately I'm up against a packaging constraint. If anyone else has any creative ideas I'd love to hear them.

Thanks again!

 

[BigInch]

I figured as much, but just thought I'd mention it.
sometimes I focus too much on one preferred solution at the expense of other methods that just might be easier.

Learn from the mistakes of others. You don't have time to make them all yourself.