Thin Moisture Barrier
Use this node to model a discontinuous moisture content across interior or exterior boundaries. By default it models a vapor barrier, with the moisture transfer coefficient β accounting for vapor diffusion only. A more general moisture barrier can be defined through the specification of a user-defined moisture transfer coefficient.
The upside and downside moisture fluxes are defined by (n ⋅ (β ⋅ n)) (ϕw,d − ϕw,u) and (n ⋅ (β ⋅ n)) (ϕw,u − ϕw,d), respectively.
Model Input
This section has fields and values that are inputs to expressions that define material properties for vapor permeability, vapor resistance factor, and saturation pressure of water vapor. If such user-defined property groups are added, the model inputs appear here.
Thin Moisture Barrier
Two options are available to define the moisture flux:
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If Vapor barrier material properties is selected (the default), the moisture transfer coefficient β is defined as
where δ is the vapor permeability of still air (SI unit: s), psat is the saturation pressure of water vapor (SI unit: Pa), μ is the vapor resistance factor (dimensionless), δp is the vapor permeability (SI unit: s), sd is the vapor diffusion equivalent air layer thickness (SI unit: m), and ds is the layer thickness (SI unit: m).
Depending on the option selected in Specify — Vapor resistance factor (the default), Vapor permeability, or Vapor diffusion equivalent air layer thickness, enter values or expressions for the needed properties, or use properties From material.
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If Moisture transfer coefficient is selected, select Isotropic, Diagonal, or Symmetric tensor type, and enter values or expressions for the tensor components of the Moisture transfer coefficient β.
See Building Material Library in the COMSOL Multiphysics Reference Manual for a description of materials containing the thermal and hygroscopic properties required by the Thin Moisture Barrier node.
Condensation Risk in a Wood-Frame Wall: Application Library path Heat_Transfer_Module/Buildings_and_Constructions/wood_frame_wall
Location in User Interface
Context Menus
Moisture Transport in Air > Thin Moisture Barrier
Moisture Transport in Building Materials > Thin Moisture Barrier
Equilibrium Moisture Transport in Porous Media > Thin Moisture Barrier
Nonequilibrium Moisture Transport in Porous Media > Thin Moisture Barrier
Ribbon
Physics tab with interface as Moisture Transport in Air, or any version of the Moisture Transport interface selected:
Boundaries > interface > Thin Moisture Barrier