Effective Diffusivity in Porous Media
The effective diffusion coefficient describes diffusion through the pore space of porous media. It is macroscopic in nature, because it is not individual pores but the entire pore space that needs to be considered. The effective diffusion coefficient for transport through the pores, De, is estimated as follows:
where:
- D is the diffusion coefficient in gas or liquid filling the pores (m2s−1)
- εt is the porosity available for the transport (dimensionless)
- δ is the constrictivity (dimensionless)
- τ is the tortuosity (dimensionless)
The transport-available porosity equals the total porosity less the pores which, due to their size, are not accessible to the diffusing particles, and less dead-end and blind pores (i.e., pores without being connected to the rest of the pore system). The constrictivity describes the slowing down of diffusion by increasing the viscosity in narrow pores as a result of greater proximity to the average pore wall. It is a function of pore diameter and the size of the diffusing particles.
Read more about this topic: Mass Diffusivity
Famous quotes containing the words effective, porous and/or media:
“I know no method to secure the repeal of bad or obnoxious laws so effective as their stringent execution.”
—Ulysses S. Grant (1822–1885)
“Does art reflect life? In movies, yes. Because more than any other art form, films have been a mirror held up to society’s porous face.”
—Marjorie Rosen (b. 1942)
“The question confronting the Church today is not any longer whether the man in the street can grasp a religious message, but how to employ the communications media so as to let him have the full impact of the Gospel message.”
—Pope John Paul II (b. 1920)