# Question about fluid dynamics (calculating concentration)

1. Feb 10, 2013

### dynamic_sample

Hi all,

I have a question about calculating the concentration of continuous air and carbon monoxide flowing through a pipe. If the gas cylinder originally has 20% CO and 80% air and it will be diluted by another gas cylinder of air, how do you account for temperature, pressure, and 'viscosity' of the gases when calculating the concentration in ppm?

2. Feb 10, 2013

### cjl

To a reasonable approximation, you can probably assume perfect mixing and get the concentration from that. Do you know the flow rates from both the original source and the diluting gas?

3. Feb 10, 2013

### dynamic_sample

Yeah, I know the flow rates from both so, I can use C1*F1=C2*F2. I'm assuming perfect mixing. Do you know how I could correct for temperature or viscosity?

4. Feb 10, 2013

### cjl

Viscosity shouldn't matter if you know the flow rate, and temperature will cause a change in the density (which could change the mass flow rate). I would probably calculate the molar flow rates of each first (based on volumetric flow rate and density), and then the concentration of the resultant mixture should be fairly easy to find.

5. Feb 10, 2013

### dynamic_sample

You know a lot more about this than I do. Thank you for your help! I found the molar flow rate in mol/min. I know this might be obvious, but I can't figure out how to calculate concentration from here. Thank you again!