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different answers from different UNDER RELAXATION FACTOR

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Old   August 18, 2012, 12:39
Default different answers from different UNDER RELAXATION FACTOR
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misagh
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Hi,
i have a 2-D micro-channel that a constant heat flux is applied on its walls.
when i change under relaxation factor or discretization of momentum and energy the result(e.g conv. heat transfer coeff.[h]) changes extensively(although the equations have been solved and converged)
what can i do?which under relaxation factor is suitable?

best regards.
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Old   August 18, 2012, 20:59
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Touré
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Do you have enough elements?
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Old   August 19, 2012, 06:10
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yes, 100'000 elements.im sure the number of elements are enough.
when i change URF in other geometries like macro scale the difference between results is less than 2 %.but in this case(microtube) changes are sever(more than40-50 %).
any guidance is appreciated.
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Old   August 19, 2012, 08:34
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It could be due to the definition of your slip condition. See pages 17 and 18 of http://ethesis.nitrkl.ac.in/1934/1/avinash.pdf
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