Discussion Forum

Hi,
I'm having problems in implementing the two phase transport in the Low-Temperature PEMFC model.
Initially, I built a model composed by the following physics:
1. Secondary Current Distribution;
2. Mixture Flow in the Cathode Channel, GDL and RL;
3. Mixture Flow in the Anode Channel, GDL and RL;
4. Cathode Gas Phase Transport of Concentrated Species: Describes the reactions occurring in the Cathode side between the gas substances and the condensation/evaporation (i.e. passage from the gas to the liquid phase and vice-versa);
5. Anode Gas Phase Transport of Concentrated Species: Describes the reactions between occurring in the Anode side between gas substances and the condensation/evaporation (i.e. passage from the gas to the liquid phase and vice-versa);
Using the Mixture Model developed by C.Y. Wang,, starting from the mixture velocity and pressure I have obtained the velocity and the pressure of the single phases.
I tried this model with imposed values of the saturation (i.e. H2O content divided by the liquid H2O density) and it provides real values.
However when I try to write the equation describing the liquid phase transport the model diverges and no solution is obtained.
To describe the liqui transport i tried two different paths:
1. I have tried to write the equation using the Mathematical Physic:
2. I used the Flow in Diluite Species by substituting to the Diffusion Coefficient the Capillary Diffusion Coefficient.
Both the two paths are not correct.
The last equation that I want to implement is:
eps*d(sl*rhol,t)+div(rhol*Ul)+div(lamdal*lambdag*K/mu*rho*(grad(pc)+(rhol-rhog)*g)))=rw
Where:
- eps: Porosity;
- sl: Liquid Saturation;
- rhol= Liquid Density;
- Ul=Liquid Velocity;
- lambdag, lambdal=Relative mobilties of the gas and liquid phases;
- K: Permeability;
- mu: Viscisity;
- rho: Mixture Density;
- pc: Capillary pressure;
- g: Gravity acceleration;
- rw: Condensation/Evaporation rate [kg/m^3/s]=if(w_H2O*p)>psat_H2O(T),100[s^-1]*eps*sg*(w_H2O*p-psat_H2O(T))*MW_H2O/R_const/T,100[s^-1]*eps*sl*(w_H2O*(p)-psat_H2O(T))*MW_H2O/R_const/T)
- sg=1-sl: Gas phase saturation;
- psat: Saturation Pressure [Pa];
- T: Temperature [K];
THe boundary conditions i have imposed are:
- Dirichlet at the cathode and anode inlet: sl=0;
- No flux in all the other boundaries.
There is someone that has been able to implement this phenomena that wants to help me? If it is required i can send via email the model.
Thank you very much.
In the file i have posted all the equation i have been used and some images to understand better what i did. In the last part of the file there are the coefficients to insert in the Mathematical model to write the equation.