BC
 

Please HELP!!!!

how & where to apply these initial condition in ansys fluent :
the CO2 concentration of each exhaled breath was set as 4% (i.e.
40,000 ppm) and the breath volume flow rate was given as 9.0 l/min
:)0

You'll want to use the species transport model and a mass flow inlet. Using species transport will allow you to track concentrations of various gases in a flow field. When you enable the model you can set the species, CO2 and probably nitrogen as the remainder, and then set the specific values in each inlet and outlet.

Check the fluent manual for more information on species transport.