Inhibiting Crystallization Fouling Using Nano-Micro-Engineered Heat Transfer Surfaces

Fouling of heat transfer surfaces is a widespread problem in the energy conversion and water treatment industries where thermally insulating deposits lead to significant performance reduction. Crystallization fouling, an important subset of fouling, occurs when water containing retrograde soluble salts like calcium sulfate, makes contact with a heated surface leading to the nucleation and growth of a surface deposit, termed “scale”. However, we currently lack detailed information on the effect of surface texture, composition, and environmental conditions on the onset of scale nucleation, growth, and adhesion which is crucial for comprehending the complexity of scaling since it is a multiphase problem that starts at the nano-micro scale. Furthermore, we lack rational strategies for passively combatting this important problem. Here we show that nano- and micro-textured superhydrophilic surfaces outperform hydrophilic, hydrophobic and superhydrophobic surfaces regarding the delay of nucleation and observable growth of forming deposits in laminar and turbulent conditions. For this purpose, a novel continuous flow experimental setup mimics a cooling section of a heat exchanger and allows to holistically investigate the onset, growth, removal of deposit with its influence on the heat transfer process. Simultaneous visual microscopic <i>in-situ</i> observation and heat transfer resistance measurements provide insight into nucleation, growth, and adhesion of nano-micro-engineered substrates. We found that the degassing of dissolved gases on the heated substrate, their affiliation to the substrate, and the subsequent evaporation of water into the new phase is important for scaling in flow conditions. We anticipate that our holistic experimental setup provides profound information on the fundamental aspects of scaling and our nano-micro-engineered surfaces contribute to the development of advanced thermal interface materials that inherently prevent and/or repel scaling to contribute to a sustainable future in energy conversion.