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[FAQ]

In case of low internal emissivity (=high reflectivity) on many surfaces in the domain the radiosity solver might still converge to the default radiosity residual of 1E-3, but the radiation heat rate report might still show a significant imbalance. To improve the radiation balance the “Residual Convergence Criteria” should be set to a lower value, i.e 1E-5. In order to achieve this value more radiation solver iterations might be required. So at the same time also the “Maximum Number of Radiation Iterations” should be increased, i.e. from the default value of 5 to a value of 30 or even 50. When convergence problems with radiation do occur, it might be helpful to investigate the radiation solver convergence alone. To do that the solution of the fluid and turbulence equations can be temporarily disabled in the Solution/Controls/Equations menu. Just deselect Flow and Turbulence, i.e. keep only Energy active. This will freeze the velocity and turbulence fields, but still have their influence included in the energy equation. Please remember to activate Flow and Turbulence again for convergence of the full system. Keywords: radiation; S2S; surface to surface; surface-to-surface; convergence; imbalance