where Nw = flux
Pw
= specific permeability, g/cm² ,s
DP = pressure across membrane
Dp = osmotic pressure difference
L = thickness of membrane
The specific permeability is an important parameter in design of
membrane operations. Some typical data (102 atm applied pressure, L
= 16 µ
, water) are:
Darcy's law applies to membranes. The coefficient is expressed in terms of the thickness of the membrane and its resistance. The driving force is the pressure differential corrected for the osmotic pressure difference.