PEEK film heat transfer surfaces for multi-effect distillation: A mechanical investigation

Multi-effect distillation (MED) is a well-established process in seawater desalination. Heat transfer surfaces used in MED-plants are exposed to highly corrosive process conditions due to direct contact to evaporating seawater. The use of polyetheretherketone (PEEK) might be a low cost and less corrodible alternative to expensive metal alloys. PEEK seems to be best suited for application in MED-plants, because it possesses an excellent mechanical and chemical resistance. One drawback of polymers is their poor thermal conductivity. Typical MED process conditions require a wall thickness of about 25 μm for PEEK to get overall heat transfer coefficients comparable to metallic heat transfer surfaces. Therefore, it is necessary to investigate the mechanical behavior of PEEK films, to ensure that they can withstand the mechanical and thermal loads in MED-plants. Stress-strain and creeping behavior of PEEK films in water were investigated at elevated temperatures and described by empirical correlations. Mechanical calculations were carried out to determine tensile loads of the polymer film in a falling film plate evaporator at typical MED process conditions. Parameter variations reveal the limitations of use for PEEK film heat transfer surfaces, but the results also show that PEEK films can withstand the mechanical loads in MED-plants