When considering an hygroscopic porous medium filled with moist air and liquid water, the coupling between the Moisture Transport and Fluid Flow interfaces applies on the moist air phase only. This means that the synchronized fluid properties (density, viscosity) are the moist air properties, and that the porosity set in the Fluid Flow interface should account for the presence of the liquid water phase in the porous medium. This can be done by multiplying the dry material porosity by (1-mt.sl), where the mt.sl variable is the liquid water saturation defined in the Moisture Transport interface. In addition, the mass source or sink in the gas phase, due to evaporation or condensation, is handled by the Moisture Flow coupling node. This moisture source term, stored in the mt.G_evap variable, cancels out with the condensation term in the equilibrium formulation that couples the gas and liquid phases, but has to be accounted for in the fluid flow equations for the gas phase. Other moisture sources, that may be defined in a Moisture Source node and stored in the mt.Gtot variable, are not accounted for, and should be manually added in the fluid flow interface if needed. See Moisture Flow in Hygroscopic Porous Medium domains for details.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is chosen in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
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When an interface is selected from the Moisture Transport list, some of its model inputs are forced with values from the Moisture Flow node. In addition, it defines how the turbulence has to be accounted for, depending on the Fluid flow interface’s turbulence settings. Therefore, each moisture transport or fluid flow interface should be used in at most one Moisture Flow node. In cases where multiple fluid flow interfaces are used, an equal number of moisture transport interfaces and Moisture Flow nodes are needed to define proper multiphysics couplings.
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If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Fluid flow or Moisture Transport lists. This behavior is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
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Evaporative Cooling of Water: Application Library path Heat_Transfer_Module/Phase_Change/evaporative_cooling
Drying of a Potato Sample: Application Library path Heat_Transfer_Module/Phase_Change/potato_drying
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when any version of a Single-Phase Flow (or Brinkman Equations, Free and Porous Media Flow) interface with Fluid Properties feature is active together with a Moisture Transport interface with Moist Air feature.
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when any version of a Single-Phase Flow (or Brinkman Equations, Free and Porous Media Flow, Darcy’s Law) interface with Fluid and Matrix Properties feature is active together with a Moisture Transport interface with Hygroscopic Porous Medium feature.
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