confusion over flow rates

Vyaas

Hi. I'm currently working with an ignition system that involves the outlet of a mixture of gases into atmospheric pressure.(the temperature just at the exit is assumed to be 200 degrees C).

Nitrogen is the predominant component. Propane is mixed well before the exit with this nitrogen and heated to about 200 degrees C. The percentage of propane in nitrogen ranges from 5 to 15%. Both components are fed into a Tee via individual sonic nozzles.

Somewhere in our calculations we encounter the "total volumetric flow rate" at the outlet.
Which of these statements is true?

1)The total volumetric flow rate is equal to the sum of the individual volumetric flow-rates of the gases (propane and nitrogen) weighted by their mass fractions.

2)The mixture "sees" atmospheric pressure at the exit and since all the components are at the same temperature, we can use Amagat's law, which says that the volumetric flowrates are summed up (without any weighting) to give the total volumetric flowrate.