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RMS Mass Vapour Convergence Issue in CFX

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Old   June 28, 2016, 03:01
Default RMS Mass Vapour Convergence Issue in CFX
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I am facing trouble in convergence of RMS Mass Vapour in CFX. All other RMS criteria are well met but RMS Mass Vapour value is 3.1E-3 and it decreases to 3E-3 after more than 150 iterations. I am dealing with subcooled boiling with constant heat flux in assembly. What should I do ? I mean could there be a way to ensure that it converges like there are under relaxation factors in Fluent. What should I do for convergence of RMS Mass Vapour in this case ? Your kind suggestions would be appreciated. Thanks!!
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Old   June 28, 2016, 06:43
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First of all: Please do not PM me with exact copies of posts on the forum. It really annoys me. If it is on the forum I will see it. I don't answer CFD questions by PM anyway.

CFX does not have the wide range of tunable Fluent has because it does not need them. The coupled solver is very robust for most applications and if it does not converge then usually it means you have a fundamental problem which cannot be fixed by simply tuning the solver constants.

As you are doing a phase change simulation you should expect problems in convergence. This FAQ will give you some general tips: http://www.cfd-online.com/Wiki/Ansys...gence_criteria
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Old   June 28, 2016, 10:10
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When I change my working fluid to water and use higher heat flux it does indeed converge . But on the other hand for any other volatile fluid at relatively lower pressure and at comparatively lower heat flux the issue remains. What do you suggest for it ?
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Old   June 28, 2016, 20:53
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Small time steps, double precision numerics, improve mesh quality. That is a starting point.
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