I am modeling coal fired boiler. For gas phase radiation I have specified P1 with cell based absorption coefficient and then changed it to domain based.

I am getting completely different answers for both cases.

1) For domain based I got peak temperature as high as 3000K where as for cell based the peak temp is 2000K which is right.

2) The difference in heat flux to water wall is as good as 100MW.

3) The values of absorption coefficient in domain based is 0.01 to 0.1 m-1 where as in case of cell based it is 0.3 to 2 m-1.

I am not able to understand this and why two approaches are giving completely different answers.

Anyone has encountered the same problem. Pl send your suggestions.

Thanks

You should use domain based, because it has no mesh dependence and it is recommended by Fluent in lectures and tutorials.