[LpSingh]

Hello everyone,
I'm trying to simulate the flow of R12 in a pipe 5 meters long and heated for a length of 3.5 meters. The heating occurs after 1 m of the pipe and ends at 4.5 m so I have divided the pipe in 3 regions with the central region heated by outside. Now, while the simulation is going I have these messages:
Temperature corrections limited on 15 cells in fluid 1
Minimum Temperature limited to 100 on 12 cells in fluid 1
I have tried to refine the mesh but I cannot get ta better result.
I have attached two screenshots about these messages and the residuals.
Thanks in advance.
L. Singh

[bluebase]

Please check your boundary conditions:
Why would a heated pipe reduce the temperature of the fluid? Does the heat flow value has the correct sign?


Do you model a phase change? Check whether your model data is given in degree Celsius or Kelvin. The same goes for the implemented boundary conditions.

Did you locate the areas in the mesh where the error originates?

[LpSingh]

Originally Posted by bluebase

Please check your boundary conditions:
Why would a heated pipe reduce the temperature of the fluid? Does the heat flow value has the correct sign?


Do you model a phase change? Check whether your model data is given in degree Celsius or Kelvin. The same goes for the implemented boundary conditions.

Did you locate the areas in the mesh where the error originates?

Thanks for your reply. The pipe intially is at 25 °C and the fluid is at 68 °C and only the central part is heated. The heat flow has a correct sign because I have observed that the temeprature in the heated pipe's wall have the highest values.
I'm adoping a boiling model and the data is given in °C so I have used the right units of measurement. For the boundary I have imposed that at the inlet the fluid has a certain mass flow rate while the outlets and the inlets before the real outlet (which would be the pipe 3 as I had to built separately the 3 pipes and then imprint them together) which has the outlet boundary condition. Then i have created adiabatic interfaces between the inner wall of the pipes and the wall of the fluid.
Only the boundary condition for the outer wall of pipe 2 has an imposed heat flux.
Unfortunately, I'm not able to identify such areas but the skewnees angle on the wall of the fluid is like 88.9 °C which is somehow too high.

I attached to this message the various screenshots.
In ss1 you can see that there is a zone at the inlet which has higher temperature with respects to the other parts.

[bluebase]

I think you're onto something. I agree, that the mesh might be an issue.


Did you do the imprinting with keeping the CAD structure? There is another default option which is doing an STL-like imprinting, which is not precise as the CAD-based imprinting. Since the pipe is a simple geometry, i suggest to keep the CAD information of your bodies as long as you can. That way some stray, weird errors of discreet geometry can be avoided. Although StarCCM's mesher is one of the most tolerant meshers i know, it still can hick up on holes, gaps, and rounding error issues in the the geometry.


How did you create the mesh, did you create as structured(/directed) mesh? I looks that way, but asking just to make sure. I assume the interfaces are fully conformal? I think in the interface object, there is a label which tells whether an interface is fully conformal or imprinted. Nonconformality will have an impact of mapping accuracy, introducing "artifacts".

[LpSingh]

Originally Posted by bluebase

I think you're onto something. I agree, that the mesh might be an issue.


Did you do the imprinting with keeping the CAD structure? There is another default option which is doing an STL-like imprinting, which is not precise as the CAD-based imprinting. Since the pipe is a simple geometry, i suggest to keep the CAD information of your bodies as long as you can. That way some stray, weird errors of discreet geometry can be avoided. Although StarCCM's mesher is one of the most tolerant meshers i know, it still can hick up on holes, gaps, and rounding error issues in the the geometry.


How did you create the mesh, did you create as structured(/directed) mesh? I looks that way, but asking just to make sure. I assume the interfaces are fully conformal? I think in the interface object, there is a label which tells whether an interface is fully conformal or imprinted. Nonconformality will have an impact of mapping accuracy, introducing "artifacts".

Yes, I kept the CAD structure. It's a directed mesh with prism layers for the fluid and the interfaces are "internal interfaces" between the 3 fluid parts and "contact interfaces" between the 3 fluid wall and 3 pipe inner wall and also between the 3 pipes intermediate inlet/outlet. So, there is written that these interfaces are of type imprinted but when I run the simulation it says that the interface are conformal. Still the two messages are there.