Influence of the interfacial free energy crystal/heat transfer surface on the induction period during fouling

The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchangers. In order to adjust the operating conditions with respect to fouling mitigation a model for the description of the entire fouling process has to be established. The main disadvantage of known models is the lack of a description of the induction period which is influenced by the nucleation rate and the adhesive strength between crystals and heat transfer surfaces. The deposition and removal process depends on the interfacial free energy crystal/heat transfer surface. For many industrial applications the only possibility to influence the interfacial free energy is to modify the surface energy characteristics of the heat transfer surface, i.e. its surface free energy. Based on the experimental investigation of the surface energy of several metallic and low energy materials their fouling performance when exposed to a liquid flow of a calcium sulphate solution was evaluated. The deployment of new surface materials such as DLC (diamond like carbon) coatings proved to be a strategy to increase the induction period.