This is a model for transport of mass without storing it; It may be used for complicated geometries where the mass diffusion Gd is determined by measurements and is assumed to be constant over the range of operations. If the component consists mainly of one type of material and a regular geometry, it may be calculated, e.g., with one of the following equations:
Diffusion for a box geometry under the assumption that mass flows along the box length:
Gd = D*A/L
D: Diffusifity (material constant)
A: Area of box
L: Length of box
Diffusion for a cylindrical geometry under the assumption that heat flows from the inside to the outside radius of the cylinder:
Gd = 2*pi*D*L/log(r_out/r_in)
pi : Modelica.Constants.pi
D : Diffusivity (material constant)
L : Length of cylinder
log : Modelica.Math.log;
r_out: Outer radius of cylinder
r_in : Inner radius of cylinder