OSN Transport Mechanisms—Theoretical Background

Although transport processes in aqueous NF systems have been studied for several years and much knowledge has been gained, OSN systems are not yet well understood. While some studies support the use of pore-flow models, others suggest using a solution-diffusion approach. The basic equations of these models are outhned below along with the major simplifying assumptions. 

Stable pores are assumed to be present inside the membrane, and the driving force for transport is the pressure gradient across the membrane. Assuming a system at constant 

Hagen-Poiseuille equation— if the membrane is assumed composed of more or less cylindrical pores  

Carman-Kozeny equation— if the membrane consists of a packed bed of particles  

This equation assumes that the swelling of the membrane separating layer is negligible and is similar to the well-known equation presented by Wijmans and Baker (1995), differing only by the ratio of which has been shown to be important when there are 

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