The Water Absorption-Desorption, H2 side and Water Absorption-Desorption, O2 side nodes are available if Electroosmotic water drag has been selected in the Membrane Transport section on the interface top node. These nodes are added by default and the selection is locked to all intersection boundaries of the Membrane and the respective Gas Phase nodes. These nodes are unavailable if Solve for electrolyte phase potential is cleared in the interface top node.

The node sets up the boundary conditions that define the absorption-desorption water flux between the membrane and the neighboring gas phase domain. The node also contributes to the boundary heat source variable, based on the Heat of water absorption parameter on the parent node.

The Absorption-Desorption Condition can be specified as Vapor absorption-desorption (by specifying an Absorption-desorption rate constant), Liquid water pressure, water Chemical potential, or User-defined rate. The default From parent option is identical to the Vapor absorption-desorption option for Vapor equilibrated model and Liquid water pressure option Liquid equilibrated model, respectively, chosen on the parent node.

The Water absorbs-desorbs as setting controls if the node should contribute to the rate variables for gaseous or liquid water. This setting is available for Chemical potential or User-defined rate options. If Gas is selected, and if the Include gas phase diffusion checkbox or the Use Darcy’s law for momentum transport checkbox has been selected in the corresponding Gas Mixture section on the interface top node, the corresponding absorption-desorption mass fluxes are added to these equations. If Liquid is selected, the corresponding absorption-desorption mass flux is added to the flux variable for H2O(l), if Include H2O(l) in reaction stoichiometry is active in the corresponding Gas Mixture section on the interface top node. Note that Vapor absorption-desorption will absorb-desorb water as for the Gas setting and Liquid water pressure as for the Liquid setting.