COMSOL 6.2 - Thin Moisture Barrier

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:

•

If 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 — (the default), , or , enter values or expressions for the needed properties, or use properties .

•

If is selected, select , , or tensor type, and enter values or expressions for the tensor components of the 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

Ribbon

Physics Tab with interface as , , or selected: