Evaporation / Two-Phase flow in a pipe / real gas model
 

Hi all,

I would like to model the evaporation of liquid nitrogen in a heated pipe. But that seems hardly possible with Fluent. As it is not ideal gas behavior and neither the Cubic Equation of State Models nor the NIST Real Gas Model are available for the two-phase region under the saturation dome (chapter 8.16 in the Fluent User Guide), it seems no suitable model (except UDF) exists? Or what about Using Real Gas Property (RGP) Table Files? Does anybody have experience with this topic?
--
Moritz

The answer from GPT
 

That is the answer from GPT

You are correct that ANSYS Fluent does not provide built-in models specifically for the two-phase region under the saturation dome for substances like liquid nitrogen. In such cases, you would typically need to use User Defined Functions (UDFs) to incorporate custom models or modify existing models to simulate the behavior you are interested in. UDFs allow you to add user-defined physics and boundary conditions to ANSYS Fluent simulations.

To model the evaporation of liquid nitrogen in a heated pipe, you can consider the following approach:

1. Create a UDF: You will need to write a custom UDF to define the evaporation behavior of liquid nitrogen. The UDF can include the equations governing mass, momentum, and energy transfer during evaporation. This UDF will need to be compiled and loaded into Fluent.

2. Define the Fluid Properties: Although the built-in models may not be available for the two-phase region under the saturation dome, you can still define the fluid properties of liquid nitrogen using the available models in Fluent. You can use the available models to define properties such as density, viscosity, and thermal conductivity for the liquid phase.

3. Define Phase Change: In the UDF, you will need to define the phase change from liquid to vapor for liquid nitrogen. This can be done by incorporating appropriate models or correlations for phase change phenomena like boiling or evaporation. You may need to refer to experimental data or existing literature to develop or validate your phase change model.

4. Apply Boundary Conditions: Set up the appropriate boundary conditions for your heated pipe simulation. Define the inlet conditions for liquid nitrogen and specify the heat transfer and pressure conditions at the pipe walls.

5. Run the Simulation: Once you have set up the UDF, defined fluid properties, and applied boundary conditions, you can run the simulation in ANSYS Fluent. The UDF will provide the custom model for the evaporation of liquid nitrogen, allowing you to simulate the desired behavior.

It's worth noting that UDF development requires programming skills and familiarity with the Fluent UDF interface. Additionally, validation and verification of the UDF against experimental data or established models are crucial to ensure the accuracy and reliability of your simulation results.

If you need further assistance with developing a UDF or specific details regarding your simulation setup, it would be helpful to consult with ANSYS Fluent documentation, support resources, or seek guidance from the ANSYS user community.