different answers from different UNDER RELAXATION FACTOR

misagh · August 18, 2012, 13:39

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.

Touré · August 18, 2012, 21:59

Do you have enough elements?

misagh · August 19, 2012, 07:10

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.

Touré · August 19, 2012, 09:34

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

August 18, 2012, 13:39	different answers from different UNDER RELAXATION FACTOR	#1
misagh Member misagh Join Date: Apr 2012 Posts: 64 Rep Power: 14	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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August 18, 2012, 21:59		#2
Touré Member Guiliguili Join Date: Aug 2010 Location: Montréal Posts: 97 Rep Power: 16	Do you have enough elements?

August 19, 2012, 07:10		#3
misagh Member misagh Join Date: Apr 2012 Posts: 64 Rep Power: 14	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.

August 19, 2012, 09:34		#4
Touré Member Guiliguili Join Date: Aug 2010 Location: Montréal Posts: 97 Rep Power: 16	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