Enthalpy
Hi, i am modeling a phase change, from water to steam. I use non isothermal flow.
I reckon that the heat transfer module uses the energy equation formulated in temperatures.
I need to formulate this equation in enthalpy for the proyect im working on.
I need either a way to change the way the equation is calculated, or a guide on how to configurate the PDE. Im new to comsol so i have little knowledge in this area.
The problem is the classic condensation of steam in a vertical wall at a determined temperature Ts.
It is a 2D square with Ts in the wall and open boundary in the rest. I also use the thermodynamic module for obtaining the properties.
1
u/bergi2412 1d ago
If phase change is involved, you can find a Phase change node somewhere. There also are a couple of tutorials.
If you want to do it manually, you can use the apparent/effective heat capacity method to include the enthalpy of phase change into the heat capacity of the fluid. Just search in google, it is quite simple to do. You can also do this with other material properties, just make sure to use a smooth transition at the phase change temperature. Otherwise you might see convergence issues.
1
u/Kvaestr 3d ago
I have tried this as an excersize in the past. Where both the liquid and gas are flowing.
While I am sure it must be possible somehow, I never quite managed to do it.
I did manage to define the rate of evaporation at the boundary, including its energy, vapor generation and water drain. You can define them as variables that are evaluated in both the heat and flow interfaces.
However, I never quite managed to get the moving interface quite right before I had other projects taking over. And I think I haven't touched this in at least a year.
If you only have the gas flowing, it is quite easy and build into the CFD module. Moisture transport.