The H2 Inlet and O2 Inlet nodes add a boundary condition for an inflow boundary, defining the composition of the mixture or mass flow rates and the flow boundary condition.

This node is available for exterior boundaries to Gas Phase nodes.

The Inlet Flow Type section is available if the Include gas phase diffusion checkbox has been selected on the interface top node. Two options are available: Mixture composition constraint (default) and Mass flow rates. If the latter is chosen, a checkbox for Stoichiometric feed also appears. Note that for certain combinations of Charge-carrying ion and Operation mode, as set in the interface top node, the default when adding a new Inlet node will be Mass flow rates with Stoichiometric feed selected.

The Mass flow rates option allows for specifying the gas feed composition by setting each individual mass flow rate, J0,i. When Stoichiometric feed is set, the gas flow rates are instead determined by setting the desired Stoichiometric current, the Stoichiometric number (which specifies the excess ratio of feed gas), and the mixture mass fractions (via Mixture specification) with the following equations:

where Jk is the feed gas mass flow rate, S is the stoichiometric number, νk is the stoichiometric coefficient of species k in the reaction, Mk is the molar mass of gas k, I is the stoichiometric current, n is the number of electrons, F is Faraday’s constant, Ji is the mass flow rate of any other gas species i, and w0,i and w0,k are the mass fractions of species i and k, respectively.

The Mixture Specification section is available if the Inlet flow type is set to Mixture composition constraint or if Mass flow rates is chosen and the Stoichiometric Feed checkbox is selected. The mixture composition can be specified using the following quantities:

Humidified mixture allows for specifying a gas mixture using values for a dry gas mixture, which is subsequently humidified to a specified relative humidity. The setting is available if H2O has been selected in the corresponding Gas Mixture section on the interface top node, and text fields are used to specify the mixture composition for all included species except H2O. Additionally, the Relative humidity, Humidification temperature, and Humidification absolute pressure of the inlet humidifier are also specified.

Humidified air is available for the O2 Inlet node, if H2O and N2 have been selected in the O2 Gas Mixture section on the interface top node. Relative humidity, Humidification temperature, and Humidification absolute pressure of the inlet humidifier are also specified. The dry mole fractions of the included species are set internally as follows: 0.79 (N2), 4e-4 (CO2) and 1e-6(CO).

Given that the humidifier (inlet) temperature (Thum), absolute pressure (pA,hum) and relative humidity (RHhum) of the humidifier (inlet) gases are known, the conversion from a set of dry (containing no water vapor) molar fraction to a corresponding humidified mixture may be calculated as follows. The water mole fraction is defined as

The Flow boundary condition section is available if the Use Darcy’s law for momentum transport checkbox has been selected on the interface top node and Stoichiometric Feed is cleared. The flow inlet condition can be specified using the From initial values, Pressure, or Total mass flow rate options.

The Boundary initial values section is available if the Use Darcy’s law for momentum transport checkbox has been selected on the interface top node or if Inlet flow type is set to Mass flow rates. The default value is From initial values, but User defined can also be selected, allowing the Boundary mass fraction initial values (if Mass flow rates is chosen) or the Boundary initial pressure (if Use Darcy’s law is chosen) to be set manually.