Design criteria for coatings in next generation condensing economizers

Surface processing of the materials used for the heat exchanging surfaces in condensing economizers and related facilities are used to deliver coatings to protect them from the corrosive condensates. By delivering increased corrosion protection, intact thermal conductivity, along with robust mechanical and wear resistance characteristics at low process costs, the lifetime of the investment is increased and the service periods become longer. However, during the past years surface processing has provided tools towards solutions for additional favorable surface features related to wetting phenomena. Coatings to enhance the dropwise condensation over the film-wise condensation, to increase the condensate collection rate and to promote the self-jumping of the condensates are far from rare. These features have a tremendous effect on the heat transfer coefficient and hence on the thermal efficiency of related heat exchange applications. Still, such features are typically not included on the testing protocols for the coatings being developed or demonstrated and they are not among the standard engineering selection criteria. In this work we briefly describe these features and provide preliminary equations for design and evaluation of their importance on the heat transfer coefficient.