Error: update_absorption_coefficient: CO2 not defined
 

Hey all,

I'm working on a combustion problem and I'm trying to incorporate thermal radiation, specifically the discrete ordinates (DO) model. After doing some research, I wanted to try out the WSGGM method for specifying absorption coefficients. From what I understand, Fluent grabs values from an internal database.

Well, when I go to initialize the solution (with WSGGM specified), Fluent gives me an error: "update_absorption_coefficient: CO2 not defined". It seems CO2 may be missing from the internal database. What's weird is there is no CO2 in my domain at all...

Is there any way to remedy this situation? Maybe there is a place to define this "update absorption coefficient"?

I think I've figured out the problem. According to the Fluent User's Manual in regards to the absorption coefficient,

"FLUENT also allows you to input a composition-dependent absorption coefficient, with the local value of a function of the local mass fractions of water vapor and carbon dioxide. This modeling option can be useful for simulation of radiation in combustion applications. The variable-absorption-coefficient model used by FLUENT is the weighted-sum-of-gray-gases model (WSGGM) described in Section 13.3.8. To activate it, select wsggm-cell-based, wsggm-domain-based, or wsggm-user-specified in the drop-down list to the right of Absorption Coefficient in the Materials panel. The three WSGGM options differ in the method used to compute the path length, as described below.

(Remember that you must first enable the species calculation in order to see the wsggm choices in the list, and CO2 and H2O must be present in the mixture.)"

My reaction doesn't produce CO2 but when I add it into the mixture materials and initialize with a 0 mass fraction of CO2, Fluent allows the initialization.

Hello , I' m studying on a combustion problem also. I m getting this problem. "Error at Node 0: update_absorption_coefficient: CO2 not defined" as same as you. I have a Pfd mixture for combustion. Where can i add co2 to the mixture as zero mass fraction.

Thanks.

Models > Species. Is this enabled?

yes, model- species and non-premixed combustion is enabled. after i had generated pdf table, i see that there is not any co2 in products. because my reaction is nh3+o2= n2 + h20 .

in this case, if i use radiation model with my solution, after initialization, an error occurs about missing of co2. i dont know what should i do.

second question is, i have calculated air fuel ratio by hand and i have found air mass flow rate 0,003268326 kg/s and fuel mass flow rate 0,000537634 kg/s. moreover, i have four air injector with dimension of 70 mm and i have defined one air inlet for all air injectors. moreover, i have six fuel injector with dimension of 42 mm and i have defined one fuel inlet for all injector. When i defined boundary conditions , should i divide total air mass flow rate to four and total fuel mass flow rate to six ? and what should i set hydraulic diameter for both air and fuel inlets.

Thanks.