Advanced materials and surface engineering strategies for mitigating fouling and corrosion in geothermal heat exchangers

Abstract Geothermal heat exchangers (GHXs) are essential in binary Organic Rankine Cycle (ORC) plants and ground-source systems but suffer significant performance degradation due to scaling, fouling, and corrosion caused by aggressive geothermal brines. Silica and carbonate scaling can reduce heat transfer capacity by 30–50%, while carbon steel components exhibit corrosion rates of 0.1–0.4 mm/y in chloride-rich environments. Fouling behaviour follows an asymptotic, linear, or falling-rate trend, depending on whether crystallisation is diffusion- or reaction-controlled, thereby significantly affecting thermal resistance and pressure drop. This review evaluates degradation mechanisms and mitigation strategies, including chemical and mechanical descaling, corrosion-resistant alloys (PREN > 40), and advanced coatings. Thermal spray coatings (e.g., WC-CoCr, TiO 2 ) enhance erosion–corrosion resistance and improve heat transfer performance, while PECVD and liquid-phase deposited oxide coatings provide conformal antifouling protection and extended service intervals. A hybrid approach combining corrosion-resistant alloys with engineered surface coatings is identified as the most promising pathway to reduce oversizing, extend service life, and improve the economic viability of geothermal plants.