The Collaborative International Dictionary of English v.0.48:

pervaporation \pervaporation\ n.
   The concentration of a colloidal solution whose colloid will
   not pass through a semipermeable membrane; the solution is
   placed in a bag of the membrane and the solvent is evaporated
   off.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

pervaporation
    n 1: the concentration of a colloidal solution whose colloid
         will not pass through a semipermeable membrane; solution is
         placed in a bag of the membrane and the solvent is
         evaporated off