Finite Element Analysis of Fluid and Solute Transport in Hemodiafiltration Membranes

Steven Conrad
Computational Dynamics Laboratory
Louisiana State University

Fluid and solute transport in hemodiafilter hollow fibers occurs through a non-trivial interaction of convection and diffusion, modulated by a number of factors that include the non-Newtonian behavior of blood, the density and viscosity dependence of blood on the local hematocrit and protein concentration, the Fahraeus-Lindquist effect on hematocrit, the osmotic effects of protein and partially reflected solutes, and the development of non-constant concentration polarization in the boundary layer along the membrane.

A two-dimensional axisymmetric COMSOL Multiphysics model was developed that included the hollow fiber, its interior blood path and exterior dialysis fluid path 10 cm in length. The membrane itself was modeled as an isotropic porous material of 50 µM in thickness having a hydraulic and diffusive permeability equal to that of the Rhône-Polenc AN69 membrane using the Brinkman and convection-diffusion application modes that included effects of osmotic pressure for protein and solutes on fluid flux.\