Permeate channel geometry to get constant separation efficiency in asymmetrical Flow Field-Flow fractionation cell with exponential breadth variation

We consider an asymmetric Flow Field-Flow fractionation cell with a specific permeate channel geometry associated with an exponential variation of the channel breadth b = b(0) exp(−sz). The hydraulic characteristic length of the membrane is constant and linked to other characteristics of the cell. We determine the dependence of permeate channel height with distance to entrance to get both mean sample channel and membrane velocities constant, hence a constant efficiency of the separation process over the whole length of the cell.