How to compute the relative humidity in Fuel Cell Simscape Model (ssc_fuel_cell) ?

In the source code of the MEA block of the fuel cell exemple, the anode and cathode relative humidity is not computed, I would like to know where and how it is computed ?

Answer 1

[Saurav]

Hey, Romeo Coletti,

I see that you want to know where and how the relative humidity calculations for the anode and cathode are made in the Membrane Electrode Assembly (MEA) block's source code.

The ‘equations’ section of the code computes the relative humidity at the anode and cathode catalyst layers (ACL and CCL, respectively). It is computed by solving for the relative humidity at the ACL and CCL by equating the mass flow rates of water vapor at the Gas Diffusion Layer (GDL) and the membrane.

Here's the relevant part of the code where this is done:

equations
    % Equate water vapor mass flow rates at GDL and membrane
    % to solve for relative humidity at ACL and CCL
    nflux_H2O_A * MW_H2O * area_cell * N_cell == mdot_H2O;
    nflux_H2O_C * MW_H2O * area_cell * N_cell == mdot_H2O + H2O_produced;

The actual relative humidity values (“RH_acl” for the anode and “RH_ccl” for the cathode) are defined in the ‘variables’ section and are used in the ‘intermediates’ section to calculate various properties and fluxes related to water transport.

The following section of the code, which specifies “RH_acl” and “RH_ccl”, can be found in source code:

variables (ExternalAccess = observe)
    i = {0, 'A'}; % Current (positive in)
    Q = {0, 'W'}; % Heat flow rate (positive in)

    RH_acl = {0.5, '1'}; % Relative humidity at anode catalyst layer (ACL)
    RH_ccl = {0.5, '1'}; % Relative humidity at cathode catalyst layer (CC)
end

I hope you find this helpful!