# RGP table for supercritical, gas and liquid phase

Member

Hello everybody,

I am working on the pipe that high pressure and temperature CO2 (P=9Mpa and T=310K) enters into the pipe and with pressure (P=5Mpa) exits.

My question is: I create a Homogenous binary mixture. In my domain, at the inlet, I have supercritical CO2 (neither liquid nor vapor). So, for the inlet, I have to specify mass fraction at the inlet. What would be the mass fraction?

I checked my model.  I tried with pressure and temperature below supercritical, P=6Mpa and T=290K and quality of CO2=0.5. The simulation converged. So I think the problem should be related to the supercritical parameters.

Any suggestion about setting supercritical parameters in the inlet and two-phase at the outlet?

Best regards

Abbas

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• GermanyForum Coordinator
edited February 2019

Have you tried with one? The interpolation should take care whether pressure above or below pcrit.

• Member
edited February 2019

Hello Amine,

What do mean with one? Do you mean that one of the inlet valve (either pressure or temperature )above the critical and another below the critical point?

Thanks

• GermanyForum Coordinator
edited February 2019

I meant mass fraction equal to one at inlet.

• Member
edited February 2019

Yes, I put 1 for a mass fraction as you can see in the picture but I got the error.

• GermanyForum Coordinator
edited February 2019
Which error?
• Member
edited February 2019

Hello Amine,

The error was outflow.

However, I just tested a simple pipe that inlet pressure is 8Mpa and inlet temperature is 305K and the outlet pressure is 7Mpa and wall temperature is 290K. I want to see that CFX is able to solve this problem or not. Now, my RGP table boundary for pressure is 0.5Mpa to 50Mpa and temperature is 250K to 550K but it says that  "Table bounds warnings at: END OF TIME STEP". How is it possible?

Best regards

Abbas

• GermanyForum Coordinator
edited February 2019

This might be possible whenever within the AMG iterative solver the dependent variable to calculate he properties are out of bounds. This might disapper at the flow evolves but might indicate wrong settings, time scale size or even small table.

• GermanyForum Coordinator
edited February 2019

And Outflow, as error is manifold, might have several roots.

• Member
edited February 2019

The problem cannot be the size of the table because the lower and upper table size for pressure and temperature are 0.5Mpa to 50Mpa and temperature is 250K to 550K and the simulation domain is a simple pipe that has one inlet and one outlet that inlet pressure is 8Mpa and inlet temperature is 305K.

• GermanyForum Coordinator
edited February 2019

So what do you think the issue is related to? As I said a super-critical Fluid is treated as being vapor.

• Member
edited February 2019

The only warning that I am receiving is "Table bounds warnings" but I am pretty sure that all domain properties are inside the table.

Best regards,

Abbas

• GermanyForum Coordinator
edited February 2019

I am sorry but cannot debug further here if you are not providing any other info. Even if you think your pressure and temperature field are within the range of the table by iterating and interpolating from IP to Nodes and doing bi-linear and tri-linear operations somethings the variable are out of bounds. The whole issue might be related to something else which I cannot figure it out without any other further statements: material, boundaries, models... You can attach the definition file here perhaps some other forum members (NON-ANSYS-STUFF) can have a look into it.

• Member
edited February 2019

I am wondering how is it possible (# case 1) for the initial condition below the critical point, simulation for simple pipe is working but for (# case 2) initial condition upper critical point I got the overflow error (when I choose homogenous binary mixture for both cases). Also, when I choose initial condition upper critical point and choose just one material (vapor CO2) the simulation is working.

Best regards

Abbas

• GermanyForum Coordinator
edited February 2019

Please add information about the boundaries used as well as the material. I will then check on my side.

• Member
edited February 2019

Thanks for your help. These are my domain and initial condition.

The material is as CO2 liquid and CO2 vapor which I generated them with ANSYS AFD.

• GermanyForum Coordinator
edited February 2019

Hi it is working for my simple pipe case with 0.5 MPa @ Inlet / 350 K, Operating Pressure 7 MPa.

@310K total temperature: one can notice that the run is not stable as the static temperature might be below the dome and the calculation is not so "easy" anymore. That is the region where the liquid become supercritical. But again it runs (simple test).

• Member
edited February 2019
Thanks Amine,

Could you give me some screen shot from your simulation such as default domain and inlet and outlet setting and also number of mesh and length and width of the tube.

Best regards
Abbas
• GermanyForum Coordinator
edited February 2019
• Member
edited February 2019

Hello Amine,

Thanks for your help. I looked into your model, we both do the same procedure but I got the Floating point exception: Overflow. I think the problem should be meshing. But, I generate mesh in ICEM that quality of mesh is between 0.75 to 1 and Orthogonal Quality higher than 0.78. Here I attached the mesh of the pipe.

best regards

Abbas

• GermanyForum Coordinator
edited February 2019

Do you get overflow even if you set higher Total Temperature @Inlet?