Hydraulic permeation model membrane parameter

The hydraulic permeation model in Eikerling ef al. helped rationalize main dependence of fhe critical currenf densify on membrane parameters. A sharply peaked 5-function-like pore size disfribufion. 

Fig. 9 Water content profiles in the membrane, calculated in the hydraulic permeation model, at various fuel-cell current densities. A typical value of the parameter / that determines the onset of membrane dehydration near the anode was estimated as / 5-10Acm for Nafion 117 [11,16]...

The hydraulic permeation model in Eikerling et al. (1998, 2007a) assumed a negligible contribution of diffiisional water flux. It is valid at sufficiently high water content. The model helped rationalizing main dependences of the critical current density on membrane parameters. A 5-function-like pore size distribution dk r)/dr = itmaxS (r - ri), which is completely determined by the maximum water uptake A- ax. and by the first moment of the pore size distribution (i.e., the average pore size), r, provided an explicit expression for jpc. ... 

In this Section, it is implicitly assumed that the mass transport resistance at the fluid-membrane interface on either side of the membrane is negligible. Also the following is information that is made available publicly by the membrane manufacturers, when not otherwise noted. As in technical processes, mass transport across semipermeable medical membranes is conveniently related to the concentration and pressme driving forces according to irreversible thermodynamics. Hence, for a two-component mixture the solute and solvent capacity to permeate a semipermeable membrane under an applied pressure and concentration gradient across the membrane can be expressed in terms of the following three parameters Lp, hydraulic permeability Pm, diffusive permeability and a, Staverman reflection coefficient (Kedem and Katchalski, 1958). All of them are more accurately measured experimentally because a limited knowledge of membrane stmcture means that theoretical models provide rather inaccurate predictions. 

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