Water Condensation-Evaporation
This subnode is available to the Gas Phase nodes when H2O has been selected, along with Include gas phase diffusion or Use Darcy’s law for momentum transport in the corresponding Gas Mixture section on the interface top node.
In low-temperature fuel cells or electrolyzers, gaseous water vapor may condensate as liquid water if the partial pressure of vapor exceeds the (equilibrium) vapor pressure as follows
The node may be used for adding an additional mass source due to water condensation–evaporation. Note that mass source may also be added to liquid water if Include H2O(l) in reaction stoichiometry is active in the corresponding Gas Mixture section on the interface top node. The Condensation-Evaporation Rate may be defined using the From vapor pressure, or by a User defined expression. The node contains text fields for specifying the Rate constant and Reference pressure, in case of the default From vapor pressure option. The rate expression is added to the rate variable for gaseous water (based on the reaction stoichiometry), which is in turn used in the domain equations for diffusion and/or Darcy’s law if these are active on the interface top node.
The Heat of reaction is calculated automatically when the Built in option is used.
The default selection is all domains of the parent node, but may be changed.