Dear all

First of all, Merry X'mas!

I am a PhD student and now conducting CFD simulation on CO2 contaminant distribution. First of all, a converged solution of velocity and temperature distribution has been obtained by a CFD program. Then the transport equation for CO2 concentration is going to be solved based on the simulated velocity and temperature field. I have three questions and would like to have valuable advices from someone.

(1) In the simulation of CO2 concentration distribution, 700ppm of CO2 is input in air supply inlet. Is it also necessary to input any ppm value of CO2 in the exhaust outlet in order to have conservation of mass (CO2)? If yes, how can I know the ppm value of CO2 near exhaust outlet before the CO2 concentration distribution simulation?

(2) Since the CFD code I am using is a non-commercial one, it seems that there is no input of the CO2 density. Then how can I tell the simulation program that the gas is CO2 or other gases? I would like to know the input method in other similar CFD program.

(3) In my CO2 concentration distribution simulation program, only maximum time iteration step is input to control when the simulation will be terminated. I would like to know in other similar program, is there any input as convergence or divergence criteria for such simulation?

Thank you very much!

Apple Chan (from Hong Kong) 22 Dec. 98

1.) Your code should be able to maintain the amount of CO_2 you introduced in the inlet. The concentration may vary, depending on your Outlet. By using a conservative Diskretisation and assuming that no chemical Reaction is taking place, you shouldn't get more or less CO_2. (CO_2 doesn't vanish ) Use zero gradient at outlet.

2.) You may use the density of your mixture. Notice that the density of mixtures may be difficult to calculate. ( Take a look at The Properties of gases and liquids: Reid,Prowsnitz ). By a Concentration of 700 ppm you may use the density of your Medium ( Air or what else you have ) If you want a more precise answer I have to know more about your Problem. You need actually should need only the mass flow rates through the boundaries of your kontroll volumes which are provided from the CFD Routines.(Finite volumes Diskretisation)

Merry Christmas and good luck