[wassli]

Hi everyone,
i am facing convergence issues with star ccm+ more specifically energy residuals are not converging and going down below e-1..
I am running steady state simulation on bare tube having super critical Freon using segregated solver. the turbulence model is SST K Omega with all y+ wall treatment.. y+ is lying within the range and i have tried lowering down the under relaxation factors...
plz help me getting energy residuals down.. i don't know where i am making mistake....
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[Mehakkar]

Check your mesh
Check that there should be no singularity point ,it is also possible that you had put the wrong boundary condition,increase the density of your mesh.

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[wassli]

Originally Posted by Mehakkar

Check your mesh
Check that there should be no singularity point ,it is also possible that you had put the wrong boundary condition,increase the density of your mesh.

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Will you please tell me about singluarity point because i do not know this term...
The boundary conditions i applied are mass flux inlet and pressure outlet with heat flux at wall...

mesh is a bit coarse but this mesh gives reliable result a lower heat fluxes. that is 20KW... but currently i have applied 40KW and trying to get mesh independence... i know the result will not b accurate but atleast the solution should get converged at coarse mesh...
the mesh pic is attached... plz check it
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[Mehakkar]

No there is no singularity

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[Mehakkar]

Can you check the meshing log

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[wassli]

I have attached pictures of mesh, wall y+, residuals and the peicewice polynomials which i fitted for properties .. but i am curious that i can not specify the solid material at wall is INCONAL 625 and fluid is tetrafluoroethane...
please can you help me how to specify introduce solid material at wall and its properites because inner dia of tube is 7.6mm and wall thickness is 4.4mm.

waiting for your kind reply
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[wassli]

other files are
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[wassli]

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[Mehakkar]

But you have to specify the material bro,without material how you can calculate the heat flux

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[Mehakkar]

And increase the fineness

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[me3840]

You need to include and mesh the solid wall in order to use your solid material properties. You only have meshed the fluid right now, therefore the solid properties are irrelevant.

I don't have much experience with that fluid, but if it's similar to air the energy solution isn't much different than the initial, therefore the residual doesn't drop much.

[wassli]

Originally Posted by me3840

You need to include and mesh the solid wall in order to use your solid material properties. You only have meshed the fluid right now, therefore the solid properties are irrelevant.

I don't have much experience with that fluid, but if it's similar to air the energy solution isn't much different than the initial, therefore the residual doesn't drop much.

Thank you so much for reply and good advice.. actually i have come to know this mistake and tried rectifying it...
i am using Inconal 625 alloy as the solid wall and my operating range for temperature is lagre to i need to incorporate the polynomial function of Cp, Density and thermal conductivity... but been unable to get the temperature dependent data for Cp and density... if you used this alloy plz refer me thermophysical properties of inconal 625...

Thank you.