Mobility
The mobility M can be related to the diffusion coefficient D by comparing the definitions in Equation 3-280 and Equation 3-283:
thus the diffusion coefficient is related to the mobility by
For transport of dilute species, there is a linear relationship between the diffusivity and the absolute temperature:
where ηc is the mobility coefficient (SI unit: s mol/kg), T is the absolute temperature, and R is the gas constant.
The mobility tensor M is then proportional to the concentration c and the mobility coefficient ηc:
so the linear mobility tensor M is related to the diffusivity as
For a quadratic dependency on the concentration, it is written as
where cmax is the concentration level at which there is no diffusion.
For User defined, it is possible enter a value or expression for the mobility tensor M.