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-   -   3D species transport model - 1 (http://www.cfd-online.com/Forums/fluent/33550-3d-species-transport-model-1-a.html)

co2 April 21, 2004 14:44

3D species transport model - 1
 
A cylindrical tank contains grain at the bottom. Grain is modeled as porous zone Tank walls are thin but are modeled as solid zone for sun radiation calculations (Heat source terms are specified in the tank walls to account for sun radiation) Grain liberates co2 gas due to grain respiration Heat is also liberated during grain respiration and has been incorporated in the engery source term in porous zone pannel I am using mixture template consisting of co2 + O2 + N2 There are no reactions involved I am using species model

question: When I run my 3D unsteady model with air as fluid I get good convergence, but the moment I switch to mixture template, my continuity residual does not go below 0.001 ----- Does anyone know why this is happening? I am sure that I have a very good mesh with 120000 cells (all hex) --- I am surprised and disappointed that I am facing this roadblock in solution to my problem -- PLEASE HELP ..


emre April 23, 2004 04:20

Re: 3D species transport model - 1
 
Hi,

I had a similar problem 3D, spe4, all hex mesh and heat xfer. I started with no species as you did. Also I ran the cold flow solution. Later on I activated species transport equations and then energy equation, (for incomp. ideal gas). Also the under-relaxtion factors were all 0.1-0.2 less than the defaults. BTW, my model did not have any porous media which may make the convergence harder.

Hope this helps Regards


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