Respected colleagues,
I am working with the Heat Transfer / Moisture Transport in Building Materials modules. Regarding the basic input material parameters, there are two options for the specification of the properties related to vapor diffusion:
· Vapor permeability, δp [s].
· Vapor resistance factor, μ [dimensionless], which is related to the previous one by δp=δ/μ, where δ [s] is the vapor permeability of still air.
In case we choose the second option, the vapor permeability of still air is automatically calculated by the software. However, I have not been able to find the expression that COMSOL uses to define it. Generally, δ is expressed through a formula of the form δ=Dv/(RT), where Dv [m^2/s] is the diffusion coefficient of water vapor in dry air at temperature T [K] and R is the gas constant of water vapor. Then, Dv responds to an empirical formulation and there are several expressions available in the literature.
I would like to know which expression is used by COMSOL for the definition of the vapor permeability of still air.
Thank you in advance for your help! Best regards, Rafael Ramirez