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Old   December 22, 2003, 14:22
Default Is the radiation solution correct?
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Hello All,

Does anyone have experience with Radiation Models in CFX 5.6? I am trying to incorporate Radiation into my model, but I am not certain I am doing things correctly:

1. How do I know if the radiation equations are converged? The solver outputs values called %lost and %imbal. What are these values and why do I care about them? Should %lost eventually go to zero?

2. Can the Discrete Transfer model be used for a pure surface to surface problem (absorption coefficient=0)? It seems to give more reasonable answers than the Monte Carlo method.

Thank you for any suggestions,

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Old   December 22, 2003, 23:28
Default Re: Is the radiation solution correct?
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%lost is the percentage of rays lost by the radiation tracker. Usually this number will be zero. However, in certain cases it can be a small number greater than zero. If it get's much larger than a few percent you will not be conserving energy and you should be careful about interpreting your answers. i.e. if you loose a ray somewhere then the energy carried by that ray goes off into never-never land.

I'm not 100% certain about %imbal, but it likely has to do with how well "balanced" the radiation equation is. i.e. how close do all the boundary radiation flows and sources add up to zero.

I don't think that DTM is a valid model for zero optical thickness (or absorption coefficient). Monte Carlo should give you better answers for surface to surface type problems. Perhaps you just need to use more photons?

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Old   December 23, 2003, 04:02
Default Re: Is the radiation solution correct?
Pascale Fonteijn
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For MC use more fotons (>1M) and probably a lower value for the Target Coarsening Rate.

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