Mitigation of crystallization fouling by local flow manipulation with wettability pattern on a flat surface

• Wettability patterned surface mitigates crystallization fouling/scaling. • Non-falling HTC characteristics with wettability patterned surface during scaling. • Environmentally friendly scale mitigation technique. • Antifouling performance with wettability patterned surface. • Enhanced flow mixing with wettability pattern on heat exchanger surface. Crystallization fouling (scaling) on the heat transfer surface is a long-lasting problem faced by multiple industry applications. The accumulated scaling layer increases both thermal and flow resistance, as a result, the energy efficiency can be significantly deteriorated with time due to the degrading heat transfer performance and the additional pumping power. For scale management, the most adopted approach is pretreating the hard water with acidic or alkaline chemicals, which not only poses substantial negative impacts to the ecosystem but also adds expenses for maintenance. In this study, a new approach is explored to mitigate crystallization fouling on the falling film flow. A millimetric-length-scale hydrophobic coated band was created on a stainless-steel surface to form a repeating wettability gradient with different orientation to the flow direction, which is expected to manipulate the local flow and disturb the local temperature and ions concentration field to suppress the crystallization process. It was found by experiment that surfaces with wettability patterns have way less calcium carbonate scale deposition, only 13–37 % of that on the baseline depending on the specific coating pattern. Observation through element energy-dispersive spectroscopy also shows only scattered deposition on the uncoated area of the patterned surfaces, while compact scaling covers the whole baseline surface. The numerical study confirms that near-wall flow disturbance exists on surfaces with the gradient, the disturbance is strongly associated with wettability bands, which modifies the local thermal and ionic environment for scale formation. The heat transfer coefficient (HTC) for the patterned samples is much higher (up to 184 % higher) and remains almost no changes with time, while the HTC of baseline sample steadily decreased by around 50 % from its initial performance. This work has demonstrated a novel approach to mitigate scaling; it provides a great potential in the heat exchanger design and scaling management.