CONCENTRATION POLARIZATION

With real substances, their build up at the membrane surface affects the driving force. The actual flux data show a leveling off as a concentration layer builds up at the membrane surface. This is called: CONCENTRATION POLARIZATION


Animation of concentration polarization.

Note how the large green molecules build up at the membrane as the small red molecules pass

Actually, the blocks for the animation of concentrations are WRONG !!
The back diffusion of the green molecules is driven by the concentration differences between the region near the membrane and the bulk concentration. It should look like the following:

Note the tiny amount of concentration polarization for the small red molecules.

To minimize concentration polarization:

  • select a membrane well suited to the process,
  • keep the concentration low if this is practical,
  • keep the pressure differential low if this is practical,
  • maintain flow across the membrane to reduce the film thickness and to scour deposits (two pump system).

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