Here u is the tangential Darcy velocity,
κ is the fracture permeability,
μ the fluid’s dynamic viscosity, and
∇tp is the tangential gradient of the fluid pressure.
The equation to solve for mass transport of species ci in a thin fracture, embedded in a porous media, is derived from
Equation 3-12. The resulting equation is:
Here dfr is the fracture thickness,
cP, i the amount of species adsorbed to (or desorbed from) the porous matrix (moles per unit dry weight of the solid),
εp is the fracture porosity, and
De is the effective diffusivity. The first two terms on the right hand side represent source terms from reactions, and
n0 corresponds to out-of plane flux from the adjacent porous domain.
Using The Transport of Diluted Species in Fractures Interface, the transport along fracture boundaries alone is solved for. In this case the transport in the surrounding porous media neglected and the out-of plane flux
n0 vanishes.