Falling film evaporation with polymeric heat transfer surfaces

The corrosive process conditions in common multi-effect distillation (MED) plants require heat transfer surfaces consisting of high-grade metal alloys. However, corrosion resistant polymers can be a reasonable alternative to expensive metals. But it is necessary to use thin polymer films, which must be mechanically stabilized by a spacer grid, to compensate the low thermal conductivity of polymers. A falling film plate evaporator with heat transfer surfaces made out of the high performance polymer polyetheretherketone (PEEK) was already developed based on those considerations. Experimentally measured overall heat transfer coefficients with the prototype heat exchanger at MED process conditions are presented in this publication. They are comparable to typical values of metallic falling film heat exchangers. Furthermore, the heat transfer within the prototype heat exchanger was modeled and compared with the obtained experimental results. It will be shown that correlations valid for falling film heat transfer on a vertical wall are not applicable for a spacer stabilized polymeric heat transfer surface, but they can be used after modifications. ► Polyetheretherketone films are used as heat transfer surfaces. ► Falling film evaporation at multi-effect distillation process conditions. ► Overall heat transfer coefficients comparable to metallic heat transfer surfaces. ► Correlations were modified to describe the heat transfer theoretically.