Learning Forum

[Ahmed Hussien]

The first step is to determine which model best suits your needs. If your goal is to capture condensation on a surface, the Eulerian Wall Film model may be the more appropriate choice. You can find additional details on the theory behind this model, as well as instructions for setting it up, in the Ansys Theory and User Guides Chapter 18: Eulerian Wall Films (ansys.com), and Chapter 28: Modeling Eulerian Wall Films (ansys.com).

 

For the Lee models, A thumb rule to tune the evaporation condensation frequency is as follows:
• If more evaporation is required, increase the evaporation frequency and reduce the condensation frequency. 
• If more condensation is required, increase the condensation frequency and reduce the evaporation frequency. 
• Though default values are set to 0.1 & 0.1 for evaporation and condensation frequencies respectively, it is observed that they may vary from 1e-3 to 1.0e5. 
• The ratio of condensation freqeuency to evaporation frequency should be roughly equal to the ratio of density of liquid to density of vapor.

➢ For water at 1bar, you may want to use evaporation-condensation frequencies of 10 and 20000, because the density values of liquid and vapor are (roughly) 1000 kg/m3 & 0.5 kg/m3. 
➢ This ratio does not have to be exactly equal but the condensation frequency have to be set to higher value to get similar mass tranfer rates for similar driving force.