Learning Forum

[Shikha Shikha]

Hi,

I am trying to simulate a flow where CO2 in two-phase (liquid+vapor mixture) is entering a pipe at a certain temperature and pressure. I also know the mass flow rate. The vapor quality of the mixture changes during the flow. Pressure will drop throughout the pipe, so the properties of the mixture will be changing as the pressure changes. How do I select the material in this case, because I couldn't find liquid CO2 in the material database in Fluent. Also, what two-phase model, and phase interaction model would you recoomend in this case? I want to track temperature in this flow to study heat transfer in this case.

[Rob]

Not all materials are in the database, some you need to find properties for elsewhere. Re which model, from reading the manual, which do you think is most suitable? 

[Shikha Shikha]

Hi Rob,

 

Thank you for your reply. I don't have access to the Ansys User Manual, but based on my understanding, I believe VOF model would work. I know I can define materials in the database, but in the case I am simulating, there will be pressure drop across the pipe, and thus the saturation temperature and properties of the material would change. I am trying to find out a way on how to account for that. I read other people on the forum suggesting to use Lee Model, but I didn't really understand how to fine tune the coefficients in the Lee Model. By default, the Lee Model is set to a constant saturation temperature, but someone recommended to import PTL (Pressure-Temperature-Latent Heat) Table to take varying saturation temperature into account. I have the property table of CO2, but without Latent Heat data, so I am trying to understand how to tell Ansys to account for the change in the saturation temperature with that table, or if there are other ways to do it.

[Rob]

You do have access to the manual, click on Help>User's Guide in Fluent. 

VOF requires the free surface to be resolved: can you afford the cell count to capture the bubble formation?

[Shikha Shikha]

Hi Rob,

 

While trying to access the User Guide, it is asking me to make an account using Customer Number, which I am unable to find. Could you help me on how I can get access to that? Also, I didn't really understand what you meant by cell count capture for bubble formation. Could you elaborate more on it? I am also trying to figure out a way to tell Ansys about varying saturation pressure throughout the flow, so that it takes into account the change in values of diiferent properties with change in saturation temperature throughout the flow. I did see an option in Lee Model to import PTL table, but I don't know the steps surrounding it to tell Ansys to take values from that table. Any suggestions?

[Rob]

Click on Help in Fluent, that should bypass the security. 

Once you've in Help, read up on how the VOF model works - that'll answer the free surface question.