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Heat exchanger, failed to evaluate variable

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I'm trying to model two counterflowing fluids (water and steam), which exchange heat through a copper surface. I'm using General Heat Transfer and Incompressible Navier-Stokes modules.

I've set up inlets and outlets in the N-S module and constant temperatures and convective fluxes in the heat transfer module. I've been messing with many settings and I may be close to solution, but now I'm getting the error:

Failed to evaluate variable U_ns
Geometry 1
Dimension 2
Domains{2}

I can't figure out what that variable is and how I could fix it. In Physics->Equation systems->Subdomain Settings I found a list of variables that has U_chns, but not U_ns. Even if it was there I wouldn't know what to do. Any ideas? I've attached the file (from COMSOL 3.4).



2 Replies Last Post 2011年3月22日 GMT-4 09:49
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 2011年3月21日 GMT-4 10:51
Hi

3.5 is too old for my versions, but is you are in "chns" and get a variable name of "ns", there must be something messed up. You should either check the underlaying equations or redo your model from fresh

--
Good luck
Ivar
Hi 3.5 is too old for my versions, but is you are in "chns" and get a variable name of "ns", there must be something messed up. You should either check the underlaying equations or redo your model from fresh -- Good luck Ivar

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Posted: 1 decade ago 2011年3月22日 GMT-4 09:49
Alright. I rebuilt the model and still got singular matrix errors like before. I finally managed to get a solution when I inserted better initial values for temperature. Still don't understand what that weird constant was, but now it's working. Thanks.
Alright. I rebuilt the model and still got singular matrix errors like before. I finally managed to get a solution when I inserted better initial values for temperature. Still don't understand what that weird constant was, but now it's working. Thanks.

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